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Archive for September, 2011

14
Sep

Service

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Industrial Repair Group performs extensive AC Drive Repair at the component level, touching up solder traces, replacing bad components, as well as full testing of ICs, PALs, EPROMs, GALs, surface mounted components and much more. Every AC Drive Repair is subjected to dynamic function tests to verify successful repair and then backed by our 18 month repair guarantee. Sealers and conformal coatings are re-applied as needed with each repair restoring your equipment back to its original OEM specs.

Industrial Repair Group is more than a service provider for your industry. We are a partner and a dedicated resource for your team members to rely upon. Feel confident that we don't play the lingo game. We are real people, with real goals. Our company is always open minded and intent on isolating problems to keep organizations up and running 24/7. We are a leading service provider that believes educated personal is the best policy.

INDUSTRIAL REPAIR GROUP FAST QUOTE

Request a Fast Quote

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Get a Repair Fast Quote Now for your AC Drive Repair

Industrial Repair Group prides ourselves on giving accurate quotes. Rest assured that our first price quote is our only price quote. Our mission statement is simple: IRG will get the job done as promised and on schedule, our customers will be satisfied, and all repairs will be backed with our 18 month repair guarantee!

Service Guarantee

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At Industrial Repair Group, our goal is to offer the best repair in the industry and the most competitive quotes. Our wide selection of services and industry leading 18 month repair guarantee are sure to provide you with the perfect repair solution for all of your industrial needs. We specialize in industrial electronics, electric motor rebuilds, and complete customer satisfaction.

ALL INDUSTRIAL REPAIR GROUP REPAIRS COME WITH AN 18 MONTH REPAIR GUARANTEE!

Summary of Warranty

Industrial Repair Group LLC. warrants to you, the ORIGINAL PURCHASER and ANY SUBSEQUENT OWNER of each Industrial Repair Group repair, for a period of one (1) year and six (6) months from the date of the repair (the "warranty period") that Industrial Repair Group's service is free of defects in materials and workmanship. We further warrant the repair regardless of the reason for failure, except as excluded in this Warranty.

Items Excluded From This Warranty

This Warranty is in effect only for failure of a Industrial Repair Group repair which occurred within the Warranty Period. It does not cover any product which has been damaged because of any intentional misuse, accident, negligence, ordinary wear and tear, cosmetic damage, or loss which is covered under any of your insurance contracts. The Industrial Repair Group Warranty also does not extend to the repaired products if the Industrial Repair Group LLC asset control number has been defaced, altered, or removed.

What Industrial Repair Group Will Do

We will remedy any defect, regardless of the reason for failure (except as excluded), by repair, replacement, or refund. We may not elect refund unless you agree, or unless we are unable to provide replacement, and repair is not practical or cannot be timely made. If a refund is elected, then you must make the defective or malfunctioning product available to us free and clear of all liens or other encumbrances. The refund will be equal to the actual repair price, not including interest, insurance, closing costs, and other finance charges less a reasonable depreciation on the product from the date of repair. Warranty work can only be performed at our fulfillment center. We will remedy the defect and ship the product from the service center within a reasonable time after receipt of the defective product. All expenses in remedying the defect, including surface shipping costs in the United States, will be borne by us. (You must bear the expense of shipping the product between any foreign country and the port of entry in the United States including the return shipment, and all taxes, duties, and other customs fees for such foreign shipments.)

How to Obtain Warranty Service

You must notify us of your need for warranty service within the warranty period. All components must be shipped in a factory pack, which, if needed, may be obtained from us free of charge. Corrective action will be taken within a reasonable time of the date of receipt of the defective product by us or our authorized service center. If the repairs made by us or our authorized service center are not satisfactory, notify us or our authorized service center immediately.

Disclaimer of Consequential and Incidental Damages.

You are not entitled to recover from us any incidental damages resulting from any defect in the Industrial Repair Group repair service. This includes any damage to another product or products resulting from such a defect.

Warranty Alterations

No person has the authority to enlarge, amend, or modify this Warranty. This Warranty is not extended by the length of time which you are deprived of the use of your equipment. Repairs and replacement parts provided under the terms of this IRG Warranty shall carry only the unexpired portion of this Industrial Repair Group Warranty.

How AC Drives Work

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Thank you for choosing Industrial Repair Group. If you would like a printable version of How AC Drives Operate, please follow this link: IRG-AC-Drive

How Variable-Frequency Drives Operate

A variable-frequency drive (VFD), also known as an AC Drive, is a system for controlling the rotational speed of an alternating current (AC) electric motor by controlling the frequency of the electrical power supplied to the motor.[1][2][3] A variable frequency drive is a specific type of adjustable-speed drive. Variable-frequency drives are also known as adjustable-frequency drives (AFD), variable-speed drives (VSD), AC drives, microdrives or inverter drives. Since the voltage is varied along with frequency, these are sometimes also called VVVF (variable voltage variable frequency) drives.

Variable-frequency drives are widely used. In ventilation systems for large buildings, variable-frequency motors on fans save energy by allowing the volume of air moved to match the system demand. They are also used on pumps, elevator, conveyor and machine tool drives.

VFD types

All VFDs use their output devices (IGBTs, transistors, thyristors) only as switches, turning them only on or off. Using a linear device such as a transistor in its linear mode is impractical for a VFD drive, since the power dissipated in the drive devices would be about as much as the power delivered to the load.

Drives can be classified as:

  • Constant voltage
  • Constant current
  • Cycloconverter

In a constant voltage converter, the intermediate DC link voltage remains approximately constant during each output cycle. In constant current drives, a large inductor is placed between the input rectifier and the output bridge, so the current delivered is nearly constant. A cycloconverter has no input rectifier or DC link and instead connects each output terminal to the appropriate input phase.

The most common type of packaged VF drive is the constant-voltage type, using pulse width modulation to control both the frequency and effective voltage applied to the motor load.

VFD system description

VFD system

A variable frequency drive system generally consists of an AC motor, a controller and an operator interface.[4][5]

VFD motor

The motor used in a VFD system is usually a three-phase induction motor. Some types of single-phase motors can be used, but three-phase motors are usually preferred. Various types of synchronous motors offer advantages in some situations, but induction motors are suitable for most purposes and are generally the most economical choice. Motors that are designed for fixed-speed operation are often used. Certain enhancements to the standard motor designs offer higher reliability and better VFD performance, such as MG-31 rated motors.[6]

VFD controller

Variable frequency drive controllers are solid state electronic power conversion devices. The usual design first converts AC input power to DC intermediate power using a rectifier or converter bridge. The rectifier is usually a three-phase, full-wave-diode bridge. The DC intermediate power is then converted to quasi-sinusoidal AC power using an inverter switching circuit. The inverter circuit is probably the most important section of the VFD, changing DC energy into three channels of AC energy that can be used by an AC motor. These units provide improved power factor, less harmonic distortion, and low sensitivity to the incoming phase sequencing than older phase controlled converter VFD’s. Since incoming power is converted to DC, many units will accept single-phase as well as three-phase input power (acting as a phase converter as well as a speed controller); however the unit must be derated when using single phase input as only part of the rectifier bridge is carrying the connected load.[7]

As new types of semiconductor switches have been introduced, these have promptly been applied to inverter circuits at all voltage and current ratings for which suitable devices are available. Introduced in the 1980s, the insulated-gate bipolar transistor (IGBT) became the device used in most VFD inverter circuits in the first decade of the 21st century.[8][9][10]

AC motor characteristics require the applied voltage to be proportionally adjusted whenever the frequency is changed in order to deliver the rated torque. For example, if a motor is designed to operate at 460 volts at 60 Hz, the applied voltage must be reduced to 230 volts when the frequency is reduced to 30 Hz. Thus the ratio of volts per hertz must be regulated to a constant value (460/60 = 7.67 V/Hz in this case). For optimum performance, some further voltage adjustment may be necessary especially at low speeds, but constant volts per hertz is the general rule. This ratio can be changed in order to change the torque delivered by the motor.[11]

In addition to this simple volts per hertz control more advanced control methods such as vector control and direct torque control (DTC) exist. These methods adjust the motor voltage in such a way that the magnetic flux and mechanical torque of the motor can be precisely controlled.

The usual method used to achieve variable motor voltage is pulse-width modulation (PWM). With PWM voltage control, the inverter switches are used to construct a quasi-sinusoidal output waveform by a series of narrow voltage pulses with pseudosinusoidal varying pulse durations.[8][12]

Operation of the motors above rated name plate speed (base speed) is possible, but is limited to conditions that do not require more power than nameplate rating of the motor. This is sometimes called “field weakening” and, for AC motors, means operating at less than rated volts/hertz and above rated name plate speed. Permanent magnet synchronous motors have quite limited field weakening speed range due to the constant magnet flux linkage. Wound rotor synchronous motors and induction motors have much wider speed range. For example, a 100 hp, 460 V, 60 Hz, 1775 RPM (4 pole) induction motor supplied with 460 V, 75 Hz (6.134 V/Hz), would be limited to 60/75 = 80% torque at 125% speed (2218.75 RPM) = 100% power.[13] At higher speeds the induction motor torque has to be limited further due to the lowering of the breakaway torque of the motor. Thus rated power can be typically produced only up to 130…150 % of the rated name plate speed. Wound rotor synchronous motors can be run even higher speeds. In rolling mill drives often 200…300 % of the base speed is used. Naturally the mechanical strength of the rotor and lifetime of the bearings is also limiting the maximum speed of the motor. It is recommended to consult the motor manufacturer if more than 150 % speed is required by the application.

PWM VFD Output Voltage Waveform

An embedded microprocessor governs the overall operation of the VFD controller. The main microprocessor programming is in firmware that is inaccessible to the VFD user. However, some degree of configuration programming and parameter adjustment is usually provided so that the user can customize the VFD controller to suit specific motor and driven equipment requirements.[8]

VFD operator interface

The operator interface provides a means for an operator to start and stop the motor and adjust the operating speed. Additional operator control functions might include reversing and switching between manual speed adjustment and automatic control from an external process control signal. The operator interface often includes an alphanumeric display and/or indication lights and meters to provide information about the operation of the drive. An operator interface keypad and display unit is often provided on the front of the VFD controller as shown in the photograph above. The keypad display can often be cable-connected and mounted a short distance from the VFD controller. Most are also provided with input and output (I/O) terminals for connecting pushbuttons, switches and other operator interface devices or control signals. A serial communications port is also often available to allow the VFD to be configured, adjusted, monitored and controlled using a computer.[8][14][15]

VFD operation

When an induction motor is connected to a full voltage supply, it draws several times (up to about 6 times) its rated current. As the load accelerates, the available torque usually drops a little and then rises to a peak while the current remains very high until the motor approaches full speed.

By contrast, when a VFD starts a motor, it initially applies a low frequency and voltage to the motor. The starting frequency is typically 2 Hz or less. Thus starting at such a low frequency avoids the high inrush current that occurs when a motor is started by simply applying the utility (mains) voltage by turning on a switch. After the start of the VFD, the applied frequency and voltage are increased at a controlled rate or ramped up to accelerate the load without drawing excessive current. This starting method typically allows a motor to develop 150% of its rated torque while the VFD is drawing less than 50% of its rated current from the mains in the low speed range. A VFD can be adjusted to produce a steady 150% starting torque from standstill right up to full speed.[16] Note, however, that cooling of the motor is usually not good in the low speed range. Thus running at low speeds even with rated torque for long periods is not possible due to overheating of the motor. If continuous operation with high torque is required in low speeds an external fan is usually needed. The manufacturer of the motor and/or the VFD should specify the cooling requirements for this mode of operation.

In principle, the current on the motor side is in direct proportion of the torque that is generated and the voltage on the motor is in direct proportion of the actual speed, while on the network side, the voltage is constant, thus the current on line side is in direct proportion of the power drawn by the motor, that is U.I or C.N where C is torque and N the speed of the motor (we shall consider losses as well, neglected in this explanation).

(1) n stands for network (grid) and m for motor

(2) C stands for torque [Nm], U for voltage [V], I for current [A], and N for speed [rad/s]

We neglect losses for the moment :

Un.In = Um.Im (same power drawn from network and from motor)

Um.Im = Cm.Nm (motor mechanical power = motor electrical power)

Given Un is a constant (network voltage) we conclude : In = Cm.Nm/Un That is “line current (network) is in direct proportion of motor power”.

With a VFD, the stopping sequence is just the opposite as the starting sequence. The frequency and voltage applied to the motor are ramped down at a controlled rate. When the frequency approaches zero, the motor is shut off. A small amount of braking torque is available to help decelerate the load a little faster than it would stop if the motor were simply switched off and allowed to coast. Additional braking torque can be obtained by adding a braking circuit (resistor controlled by a transistor) to dissipate the braking energy. With 4-quadrants rectifiers (active-front-end), the VFD is able to brake the load by applying a reverse torque and reverting the energy back to the network.

Power line harmonics

While PWM allows for nearly sinusoidal currents to be applied to a motor load, the diode rectifier of the VFD takes roughly square-wave current pulses out of the AC grid, creating harmonic distortion in the power line voltage. When the VFD load size is small and the available utility power is large, the effects of VFD systems slicing small chunks out of AC grid generally go unnoticed. Further, in low voltage networks the harmonics caused by single phase equipment such as computers and TVs are such that they are partially cancelled by three-phase diode bridge harmonics.

However, when either a large number of low-current VFDs, or just a few very large-load VFDs are used, they can have a cumulative negative impact on the AC voltages available to other utility customers in the same grid.

When the utility voltage becomes misshapen and distorted the losses in other loads such as normal AC motors are increased. This may in the worst case lead to overheating and shorter operation life. Also substation transformers and compensation capacitors are affected, the latter especially if resonances are aroused by the harmonics.

In order to limit the voltage distortion the owner of the VFDs may be required to install filtering equipment to smooth out the irregular waveform. Alternately, the utility may choose to install filtering equipment of its own at substations affected by the large amount of VFD equipment being used. In high power installations decrease of the harmonics can be obtained by supplying the VSDs from transformers that have different phase shift.[17]

Further, it is possible to use instead of the diode rectifier a similar transistor circuit that is used to control the motor. This kind of rectifier is called active infeed converter in IEC standards. However, manufacturers call it by several names such as active rectifier, ISU (IGBT Supply Unit), AFE (Active Front End) or four quadrant rectifier. With PWM control of the transistors and filter inductors in the supply lines the AC current can be made nearly sinusoidal. Even better attenuation of the harmonics can be obtained by using an LCL (inductor-capacitor-inductor) filter instead of single three-phase filter inductor.

Additional advantage of the active infeed converter over the diode bridge is its ability to feed back the energy from the DC side to the AC grid. Thus no braking resistor is needed and the efficiency of the drive is improved if the drive is frequently required to brake the motor.

Application considerations

The output voltage of a PWM VFD consists of a train of pulses switched at the carrier frequency. Because of the rapid rise time of these pulses, transmission line effects of the cable between the drive and motor must be considered. Since the transmission-line impedance of the cable and motor are different, pulses tend to reflect back from the motor terminals into the cable. The resulting voltages can produce up to twice the rated line voltage for long cable runs, putting high stress on the cable and motor winding and eventual insulation failure. Increasing the cable or motor size/type for long runs and 480v or 600v motors will help offset the stresses imposed upon the equipment due to the VFD (modern 230v single phase motors not effected). At 460 V, the maximum recommended cable distances between VFDs and motors can vary by a factor of 2.5:1. The longer cables distances are allowed at the lower Carrier Switching Frequencies (CSF) of 2.5 kHz. The lower CSF can produce audible noise at the motors. For applications requiring long motor cables VSD manufacturers usually offer du/dt filters that decrease the steepness of the pulses. For very long cables or old motors with insufficient winding insulation more efficient sinus filter is recommended. Expect the older motor’s life to shorten. Purchase VFD rated motors for the application.

Further, the rapid rise time of the pulses may cause trouble with the motor bearings. The stray capacitance of the windings provide paths for high frequency currents that close through the bearings. If the voltage between the shaft and the shield of the motor exceeds few volts the stored charge is discharged as a small spark. Repeated sparking causes erosion in the bearing surface that can be seen as fluting pattern. In order to prevent sparking the motor cable should provide a low impedance return path from the motor frame back to the inverter. Thus it is essential to use a cable designed to be used with VSDs.[18]

In big motors a slip ring with brush can be used to provide a bypass path for the bearing currents. Alternatively isolated bearings can be used.

The 2.5 kHz and 5 kHz CSFs cause fewer motor bearing problems than the 20 kHz CSFs.[19] Shorter cables are recommended at the higher CSF of 20 kHz. The minimum CSF for synchronize tracking of multiple conveyors is 8 kHz.

The high frequency current ripple in the motor cables may also cause interference with other cabling in the building. This is another reason to use a motor cable designed for VSDs that has a symmetrical three-phase structure and good shielding. Further, it is highly recommended to route the motor cables as far away from signal cables as possible.[20]

Available VFD power ratings

Variable frequency drives are available with voltage and current ratings to match the majority of 3-phase motors that are manufactured for operation from utility (mains) power. VFD controllers designed to operate at 111 V to 690 V are often classified as low voltage units. Low voltage units are typically designed for use with motors rated to deliver 0.2 kW or 1/4 horsepower (hp) up to several megawatts. For example, the largest ABB ACS800 single drives are rated for 5.6 MW[21] . Medium voltage VFD controllers are designed to operate at 2,400/4,162 V (60 Hz), 3,000 V (50 Hz) or up to 10 kV. In some applications a step up transformer is placed between a low voltage drive and a medium voltage load. Medium voltage units are typically designed for use with motors rated to deliver 375 kW or 500 hp and above. Medium voltage drives rated above 7 kV and 5,000 or 10,000 hp should probably be considered to be one-of-a-kind (one-off) designs.[22]

Medium voltage drives are generally rated amongst the following voltages : 2,3 KV – 3,3 Kv – 4 Kv – 6 Kv – 11 Kv

The in-between voltages are generally possible as well. The power of MV drives is generally in the range of 0,3 to 100 MW however involving a range a several different type of drives with different technologies.

Dynamic braking

Using the motor as a generator to absorb energy from the system is called dynamic braking. Dynamic braking stops the system more quickly than coasting. Since dynamic braking requires relative motion of the motor’s parts, it becomes less effective at low speed and cannot be used to hold a load at a stopped position. During normal braking of an electric motor the electrical energy produced by the motor is dissipated as heat inside of the rotor, which increases the likelihood of damage and eventual failure. Therefore, some systems transfer this energy to an outside bank of resistors. Cooling fans may be used to protect the resistors from damage. Modern systems have thermal monitoring, so if the temperature of the bank becomes excessive, it will be switched off.[23]

Regenerative variable-frequency drives

Regenerative AC drives have the capacity to recover the braking energy of an overhauling load and return it to the power system.[24]

Line regenerative variable frequency drives, showing capacitors(top cylinders)and inductors attached which filter the regenerated power.

[2][3][24][25][26][27]

Cycloconverters and current-source inverters inherently allow return of energy from the load to the line; voltage-source inverters require an additional converter to return energy to the supply.[28]

Regeneration is only useful in variable-frequency drives where the value of the recovered energy is large compared to the extra cost of a regenerative system,[28] and if the system requires frequent braking and starting. An example would be use in conveyor belt during manufacturing where it should stop for every few minutes, so that the parts can be assembled correctly and moves on. Another example is a crane, where the hoist motor stops and reverses frequently, and braking is required to slow the load during lowering. Regenerative variable-frequency drives are widely used where speed control of overhauling loads is required.

Brushless DC motor drives

Much of the same logic contained in large, powerful VFDs is also embedded in small brushless DC motors such as those commonly used in computer fans. In this case, the chopper usually converts a low DC voltage (such as 12 volts) to the three-phase current used to drive the electromagnets that turn the permanent magnet rotor.

See also

  • Regenerative variable-Frequency drives
  • Direct torque control
  • Frequency changer
  • Space Vector Modulation
  • Variable speed air compressor
  • Vector control (motor)
Category : AC Drive Repair | AC, DC, VFD, Servo Drives | Industrial Controls Repair | Blog
8
Sep

INDUSTRIAL REPAIR GROUP FAST QUOTE
Industrial Repair Group performs extensive component level repairs, touching up solder traces, replacing bad components, as well as full testing of ICs, PALs, EPROMs, GALs, surface mounted components and much more. Every Power Supply Repair is subjected to dynamic function tests to verify successful repair and then backed by our 18 month repair guarantee. Sealers and conformal coatings are re-applied as needed with each repair restoring your equipment back to its original OEM specs.

To find out more about Industrial Repair Group’s Power Supply Repair Service, click here: Industrial Repair Group’s Power Supply Repair Service

A power supply is a device that supplies electrical energy to one or more electric loads. The term is most commonly applied to devices that convert one form of electrical energy to another, though it may also refer to devices that convert another form of energy (e.g., mechanical, chemical, solar) to electrical energy. A regulated power supply is one that controls the output voltage or current to a specific value; the controlled value is held nearly constant despite variations in either load current or the voltage supplied by the power supply’s energy source.

Every power supply must obtain the energy it supplies to its load, as well as any energy it consumes while performing that task, from an energy source. Depending on its design, a power supply may obtain energy from:

  • Electrical energy transmission systems. Common examples of this include power supplies that convert AC line voltage to DC voltage.
  • Energy storage devices such as batteries and fuel cells.
  • Electromechanical systems such as generators and alternators.
  • Solar power.

A power supply may be implemented as a discrete, stand-alone device or as an integral device that is hardwired to its load. In the latter case, for example, low voltage DC power supplies are commonly integrated with their loads in devices such as computers and household electronics.

Constraints that commonly affect power supplies include:

  • The amount of voltage and current they can supply.
  • How long they can supply energy without needing some kind of refueling or recharging (applies to power supplies that employ portable energy sources).
  • How stable their output voltage or current is under varying load conditions.
  • Whether they provide continuous or pulsed energy.

Power supplies types

Power supplies for electronic devices can be broadly divided into linear and switching power supplies. The linear supply is usually a relatively simple design, but it becomes increasingly bulky and heavy for high-current equipment due to the need for large mains-frequency transformers and heat-sinked electronic regulation circuitry. Linear voltage regulators produce regulated output voltage by means of an active voltage divider that consumes energy, thus making efficiency low. A switched-mode supply of the same rating as a linear supply will be smaller, is usually more efficient, but will be more complex.

Battery

A battery is an alternative to a line-operated power supply;[1] it is independent of the availability of mains electricity, suitable for portable equipment and use in locations without mains power. A battery consists of several electrochemical cells connected in series to provide the voltage desired. Batteries may be primary (able to supply current when constructed, discarded when drained) or secondary (rechargeable; can be charged, used, and recharged many times)

The primary cell first used was the carbon-zinc dry cell.[1] It had a voltage of 1.5 volts; later battery types have been manufactured, when possible, to give the same voltage per cell. Carbon-zinc and related cells are still used, but the alkaline battery delivers more energy per unit weight and is widely used. The most commonly used battery voltages are 1.5 (1 cell) and 9V (6 cells).

Various technologies of rechargeable battery are used. Types most commonly used are NiMH, and lithium ion and variants.

DC power supply

A home-made linear power supply (used here to power amateur radio equipment)

An AC powered unregulated power supply usually uses a transformer to convert the voltage from the wall outlet (mains) to a different, nowadays usually lower, voltage. If it is used to produce DC, a rectifier is used to convert alternating voltage to a pulsating direct voltage, followed by a filter, comprising one or more capacitors, resistors, and sometimes inductors, to filter out (smooth) most of the pulsation. A small remaining unwanted alternating voltage component at mains or twice mains power frequency (depending upon whether half- or full-wave rectification is used)—ripple—is unavoidably superimposed on the direct output voltage.

For purposes such as charging batteries the ripple is not a problem, and the simplest unregulated mains-powered DC power supply circuit consists of a transformer driving a single diode in series with a resistor.

Before the introduction of solid-state electronics, equipment used valves (vacuum tubes) which required high voltages; power supplies used step-up transformers, rectifiers, and filters to generate one or more direct voltages of some hundreds of volts, and a low alternating voltage for filaments. Only the most advanced equipment used expensive and bulky regulated power supplies.

AC power supply

An AC power supply typically takes the voltage from a wall outlet (mains supply, often 230v in Europe) and lowers it to the desired voltage (eg 9vac). As well as lowering the voltage some filtering may take place. An example use for an AC power supply is powering certain guitar effects pedals (e.g. the Digitech Whammy pedal) although it is more common for effects pedals to require DC.

Linear regulated power supply

The voltage produced by an unregulated power supply will vary depending on the load and on variations in the AC supply voltage. For critical electronics applications a linear regulator may be used to set the voltage to a precise value, stabilized against fluctuations in input voltage and load. The regulator also greatly reduces the ripple and noise in the output direct current. Linear regulators often provide current limiting, protecting the power supply and attached circuit from overcurrent.

Adjustable linear power supplies are common laboratory and service shop test equipment, allowing the output voltage to be adjusted over a range. For example, a bench power supply used by circuit designers may be adjustable up to 30 volts and up to 5 amperes output. Some can be driven by an external signal, for example, for applications requiring a pulsed output.

AC/DC supply

Main article: AC/DC (electricity)

In the past, mains electricity was supplied as DC in some regions, AC in others. Transformers cannot be used for DC, but a simple, cheap unregulated power supply could run directly from either AC or DC mains without using a transformer. The power supply consisted of a rectifier and a filter capacitor. When operating from DC, the rectifier was essentially a conductor, having no effect; it was included to allow operation from AC or DC without modification.

Switched-mode power supply

Main article: Switched-mode power supply

A computer’s switched mode power supply unit.

A switched-mode power supply (SMPS) works on a different principle. AC input, usually at mains voltage, is rectified without the use of a mains transformer, to obtain a DC voltage. This voltage is then switched on and off at a high speed by electronic switching circuitry, which may then pass through a high-frequency, hence small, light, and cheap, transformer or inductor. The duty cycle of the output square wave increases as power output requirements increase. Switched-mode power supplies are always regulated. If the SMPS uses a properly-insulated high-frequency transformer, the output will be electrically isolated from the mains, essential for safety.

The input power slicing occurs at a very high speed (typically 10 kHz — 1 MHz). High frequency and high voltages in this first stage permit much smaller transformers and smoothing capacitors than in a power supply operating at mains frequency, as linear supplies do. After the transformer secondary, the AC is again rectified to DC. To keep output voltage constant, the power supply needs a sophisticated feedback controller to monitor current drawn by the load.

SMPSs often include safety features such as current limiting or a crowbar circuit to help protect the device and the user from harm.[2] In the event that an abnormal high-current power draw is detected, the switched-mode supply can assume this is a direct short and will shut itself down before damage is done. For decades PC power supplies have provided a power good signal to the motherboard whose absence prevents operation when abnormal supply voltages are present.

SMPSs have an absolute limit on their minimum current output.[3] They are only able to output above a certain power level and cannot function below that point. In a no-load condition the frequency of the power slicing circuit increases to great speed, causing the isolated transformer to act as a Tesla coil, causing damage due to the resulting very high voltage power spikes. Switched-mode supplies with protection circuits may briefly turn on but then shut down when no load has been detected. A very small low-power dummy load such as a ceramic power resistor or 10-watt light bulb can be attached to the supply to allow it to run with no primary load attached.

Power factor has become a recent issue of concern for computer manufacturers. Switched mode power supplies have traditionally been a source of power line harmonics and have a very poor power factor. Many computer power supplies built in the last few years now include power factor correction built right into the switched-mode supply, and may advertise the fact that they offer 1.0 power factor.

By slicing up the sinusoidal AC wave into very small discrete pieces, a portion of unused alternating current stays in the power line as very small spikes of power that cannot be utilized by AC motors and results in waste heating of power line transformers. Hundreds of switched mode power supplies in a building can result in poor power quality for other customers surrounding that building, and high electric bills for the company if they are billed according to their power factor in addition to the actual power used. Filtering capacitor banks may be needed on the building power mains to suppress and absorb these negative power factor effects[citation needed].

Programmable power supply

Programmable power supplies

Programmable power supplies allow for remote control of the output voltage through an analog input signal or a computer interface such as RS232 or GPIB. Variable properties include voltage, current, and frequency (for AC output units). These supplies are composed of a processor, voltage/current programming circuits, current shunt, and voltage/current read-back circuits. Additional features can include overcurrent, overvoltage, and short circuit protection, and temperature compensation. Programmable power supplies also come in a variety of forms including modular, board-mounted, wall-mounted, floor-mounted or bench top.

Programmable power supplies can furnish DC, AC, or AC with a DC offset. The AC output can be either single-phase or three-phase. Single-phase is generally used for low-voltage, while three-phase is more common for high-voltage power supplies.

Programmable power supplies are now used in many applications. Some examples include automated equipment testing, crystal growth monitoring, and differential thermal analysis.[4]

Uninterruptible power supply

Main article: Uninterruptible power supply

An uninterruptible power supply (UPS) takes its power from two or more sources simultaneously. It is usually powered directly from the AC mains, while simultaneously charging a storage battery. Should there be a dropout or failure of the mains, the battery instantly takes over so that the load never experiences an interruption. Such a scheme can supply power as long as the battery charge suffices, e.g., in a computer installation, giving the operator sufficient time to effect an orderly system shutdown without loss of data. Other UPS schemes may use an internal combustion engine or turbine to continuously supply power to a system in parallel with power coming from the AC . The engine-driven generators would normally be idling, but could come to full power in a matter of a few seconds in order to keep vital equipment running without interruption. Such a scheme might be found in hospitals or telephone central offices.

High-voltage power supply

High voltage refers to an output on the order of hundreds or thousands of volts. High-voltage supplies use a linear setup to produce an output voltage in this range.

Additional features available on high-voltage supplies can include the ability to reverse the output polarity along with the use of circuit breakers and special connectors intended to minimize arcing and accidental contact with human hands. Some supplies provide analog inputs (i.e. 0-10V) that can be used to control the output voltage, effectively turning them into high-voltage amplifiers albeit with very limited bandwidth.

Voltage multipliers

Voltage multipliers, as the name implies, are circuits designed to multiply the input voltage. The input voltage may be doubled (voltage doubler), tripled (voltage tripler), quadrupled (voltage quadrupler), etc. Voltage multipliers are also power converters. An AC input is converted to a higher DC output. These circuits allow high voltages to be obtained using a much lower voltage AC source.

Typically, voltage multipliers are composed of half-wave rectifiers, capacitors, and diodes. For example, a voltage tripler consists of three half-wave rectifiers, three capacitors, and three diodes (see Cockcroft Walton Multiplier). Full-wave rectifiers may be used in a different configuration to achieve even higher voltages. Also, both parallel and series configurations are available. For parallel multipliers, a higher voltage rating is required at each consecutive multiplication stage, but less capacitance is required. The voltage capability of the capacitor limits the maximum output voltage.

Voltage multipliers have many applications. For example, voltage multipliers can be found in everyday items like televisions and photocopiers. Even more applications can be found in the laboratory, such as cathode ray tubes, oscilloscopes, and photomultiplier tubes.[5][6]

Power supply applications

Computer power supply

Main article: Computer power supply

A modern computer power supply is a switch with on and off supply designed to convert 110-240 V AC power from the mains supply, to several output both positive (and historically negative) DC voltages in the range + 12V,-12V,+5V,+5VBs and +3.3V. The first generation of computers power supplies were linear devices, but as cost became a driving factor, and weight became important, switched mode supplies are almost universal.

The diverse collection of output voltages also have widely varying current draw requirements, which are difficult to all be supplied from the same switched-mode source. Consequently most modern computer power supplies actually consist of several different switched mode supplies, each producing just one voltage component and each able to vary its output based on component power requirements, and all are linked together to shut down as a group in the event of a fault condition.

Welding power supply

Main article: Welding power supply

Arc welding uses electricity to melt the surfaces of the metals in order to join them together through coalescence. The electricity is provided by a welding power supply, and can either be AC or DC. Arc welding typically requires high currents typically between 100 and 350 amps. Some types of welding can use as few as 10 amps, while some applications of spot welding employ currents as high as 60,000 amps for an extremely short time. Older welding power supplies consisted of transformers or engines driving generators. More recent supplies use semiconductors and microprocessors reducing their size and weight.

AC adapter

Switched mode mobile phone charger

Main article: AC adapter

A linear or switched-mode power supply (or in some cases just a transformer) that is built into the top of a plug is known as a “plug pack”, “plug-in adapter”, “adapter block”, “domestic mains adapter” or just “power adapter”. Slang terms include “wall wart” and “power brick”. They are even more diverse than their names; often with either the same kind of DC plug offering different voltage or polarity, or a different plug offering the same voltage. “Universal” adapters attempt to replace missing or damaged ones, using multiple plugs and selectors for different voltages and polarities. Replacement power supplies must match the voltage of, and supply at least as much current as, the original power supply.

The least expensive AC units consist solely of a small transformer, while DC adapters include a few additional diodes. Whether or not a load is connected to the power adapter, the transformer has a magnetic field continuously present and normally cannot be completely turned off unless unplugged.

Because they consume standby power, they are sometimes known as “electricity vampires” and may be plugged into a power strip to allow turning them off. Expensive switched-mode power supplies can cut off leaky electrolyte-capacitors, use powerless MOSFETs, and reduce their working frequency to get a gulp of energy once in a while to power, for example, a clock, which would otherwise need a battery.

Overload protection

Power supplies often include some type of overload protection that protects the power supply from load faults (e.g., short circuits) that might otherwise cause damage by overheating components or, in the worst case, electrical fire. Fuses and circuit breakers are two commonly used mechanisms for overload protection.[1]

Fuses

A fuse is a piece of wire, often in a casing that improves its electrical characteristics. If too much current flows, the wire becomes hot and melts. This effectively disconnects the power supply from its load, and the equipment stops working until the problem that caused the overload is identified and the fuse is replaced.

There are various types of fuses used in power supplies.

  • fast blow fuses cut the power as quick as they can
  • slow blow fuses tolerate more short term overload
  • wire link fuses are just an open piece of wire, and have poorer overload characteristics than glass and ceramic fuses

Some power supplies use a very thin wire link soldered in place as a fuse.

Circuit breakers

One benefit of using a circuit breaker as opposed to a fuse is that it can simply be reset instead of having to replace the blown fuse. A circuit breaker contains an element that heats, bends and triggers a spring which shuts the circuit down. Once the element cools, and the problem is identified the breaker can be reset and the power restored.

Thermal cutouts

Some PSUs use a thermal cutout buried in the transformer rather than a fuse. The advantage is it allows greater current to be drawn for limited time than the unit can supply continuously. Some such cutouts are self resetting, some are single use only.

Current limiting

Some supplies use current limiting instead of cutting off power if overloaded. The two types of current limiting used are electronic limiting and impedance limiting. The former is common on lab bench PSUs, the latter is common on supplies of less than 3 watts output.

A foldback current limiter reduces the output current to much less than the maximum non-fault current.

Power conversion

The term “power supply” is sometimes restricted to those devices that convert some other form of energy into electricity (such as solar power and fuel cells and generators). A more accurate term for devices that convert one form of electric power into another form (such as transformers and linear regulators) is power converter. The most common conversion is from AC to DC.

Mechanical power supplies

  • Flywheels coupled to electrical generators or alternators
  • Compulsators
  • Explosively pumped flux compression generators

Terminology

  • SCP – Short circuit protection
  • OPP – Overpower (overload) protection
  • OCP – Overcurrent protection
  • OTP – Overtemperature protection
  • OVP – Overvoltage protection
  • UVP – Undervoltage protection
  • UPS – Uninterruptable Power Supply
  • PSU – Power Supply Unit
  • SMPSU – Switch-Mode Power Supply Unit

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Category : Industrial Controls Repair | Industrial Repair Group | Industrial Repair Service | Blog
7
Sep

INDUSTRIAL REPAIR GROUP FAST QUOTE Industrial Repair Group performs extensive component level repairs, touching up solder traces, replacing bad components, as well as full testing of ICs, PALs, EPROMs, GALs, surface mounted components and much more. Every Amateur Radio Amplifier Repair (HAM) is subjected to dynamic function tests to verify successful repair and then backed by our 18 month repair guarantee. Sealers and conformal coatings are re-applied as needed with each repair restoring your equipment back to its original OEM specs.

To find out more about Industrial Repair Group’s Amateur Radio Amplifier Repair Service, click here: Amateur Radio Amplifier Repair Service (HAM)

An example of an amateur radio station with four transceivers, amplifiers, and a computer for logging and for digital modes. On the wall are examples of various awards, certificates, and a reception report card (QSL card) from a foreign amateur station.

Amateur radio (also called ham radio) is the use of designated radio frequency spectrum for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication. The term “amateur” is used to specify persons interested in radio technique solely with a personal aim and without pecuniary interest, and to differentiate it from commercial broadcasting, public safety (such as police and fire) or professional two-way radio services (such as taxis, etc). Amateur radio operation is coordinated by the International Telecommunication Union (ITU) and licensed by the individual national governments that regulate technical and operational characteristics of transmissions and issue individual stations with an identifying call sign. Prospective amateur operators are tested for their understanding of key concepts in electronics and the host government’s radio regulations. Amateurs use a variety of voice, text, image and data communications modes and have access to frequency allocations throughout the RF spectrum to enable communication across a city, a region, a country, a continent or the whole world. An estimated two million people throughout the world are regularly involved with amateur radio.[1]

History

Main article: History of amateur radio

The origins of amateur radio can be traced to the late 19th century though amateur radio, as practiced today, did not begin until the early 20th century. The first listing of amateur radio communications receivers is contained in the First Annual Official Wireless Blue Book of the Wireless Association of America in 1909.[2] This first radio callbook lists wireless telegraph stations in Canada and the United States, including 89 amateur radio stations. As with radio in general, the birth of amateur radio was strongly associated with various amateur experimenters and hobbyists. Throughout its history, amateur radio enthusiasts have made significant contributions to science, engineering, industry, and social services. Research by amateur radio operators has founded new industries,[3] built economies,[4] empowered nations,[5] and saved lives in times of emergency.[6][7]

Activities and practices

Specialized Interests and modes
While many hams simply enjoy talking to friends, others pursue a wide variety of specialized interests.

  • Amateur Radio Direction Finding, also known as “Fox hunting”
  • Amateur radio emergency communications
  • Amateur television
  • Communicating via amateur satellites
  • Contesting, earning awards, and collecting QSL cards
  • Designing new antennas
  • DX communication to far away countries
  • DX-peditions
  • Hamfests, club meetings and swap meets
  • Hand building homebrew amateur radio gear
  • High speed multimedia
  • High Speed Telegraphy
  • Packet radio
  • Portable, fixed, mobile and handheld operation
  • Low-power operation (QRP).
  • Severe weather spotting
  • Tracking tactical information using the Automatic Packet Reporting System (APRS), which may integrate with the GPS
  • Using the Internet Radio Linking Project (IRLP) to connect radio repeaters via the Internet
  • VHF, UHF and microwave operation on amateur radio high bands
  • Vintage amateur radios, such as those using vacuum tube technology
v · d · e

Amateur radio operators use various modes of transmission to communicate. The two most common modes for voice transmissions are frequency modulation (FM) and single sideband (SSB). FM offers high quality audio signals, while SSB is better at long distance communication when bandwidth is restricted. [8]

Radiotelegraphy using Morse code (also known as “CW” from “continuous wave”) is an activity dating to the earliest days of radio. It is the wireless extension of land line (wire based) telegraphy developed by Samuel Morse and was the predominant real time long-distance communication method of the 19th century. Though computer-based (digital) modes and methods have largely replaced CW for commercial and military applications, many amateur radio operators still enjoy using the CW mode, particularly on the shortwave bands and for experimental work such as earth-moon-earth communication, with its inherent signal-to-noise ratio advantages. Morse, using internationally agreed message encodings such as the Q code, enables communication between amateurs who speak different languages. It is also popular with homebrewers as CW-only transmitters are simpler to construct. A similar “legacy” mode popular with home constructors is amplitude modulation (AM), pursued by many vintage amateur radio enthusiasts and aficionados of vacuum tube technology.

Demonstrating a proficiency in Morse code was for many years a requirement to obtain amateur licenses for the high frequency bands (frequencies below 30 MHz). Following changes in international regulations in 2003 countries are no longer required to demand proficiency.[9] The United States Federal Communications Commission, for example, phased out this requirement for all license classes on February 23, 2007.[10][11]

Modern personal computers have encouraged the use of digital modes such as radioteletype (RTTY) which previously required cumbersome mechanical equipment.[12] Hams led the development of packet radio in the 1970s, which has employed protocols such as TCP/IP since the 1980s. Specialized digital modes such as PSK31 allow real-time, low-power communications on the shortwave bands. Echolink using Voice over IP technology has enabled amateurs to communicate through local Internet-connected repeaters and radio nodes,[13] while IRLP has allowed the linking of repeaters to provide greater coverage area. Automatic link establishment (ALE) has enabled continuous amateur radio networks to operate on the high frequency bands with global coverage. Other modes, such as FSK441 using software such as WSJT, are used for weak signal modes including meteor scatter and moonbounce communications.

Fast scan amateur television has gained popularity as hobbyists adapt inexpensive consumer video electronics like camcorders and video cards in PCs. Because of the wide bandwidth and stable signals required, amateur television is typically found in the 70 cm (420 MHz–450 MHz) frequency range, though there is also limited use on 33 cm (902 MHz–928 MHz), 23 cm (1240 MHz–1300 MHz) and higher. These requirements also effectively limit the signal range to between 20 and 60 miles (30 km–100 km). The use of linked repeater systems, however, can allow transmissions across hundreds of miles.[14]

These repeaters, or automated relay stations, are used on VHF and higher frequencies to increase signal range. Repeaters are usually located on top of a mountain, hill, or tall building and allow operators to communicate over hundreds of square miles using a low power hand-held transceiver. Repeaters can also be linked together by use of other amateur radio bands, landline, or the Internet.

NASA astronaut Col. Doug Wheelock, KF5BOC, Expedition 24 flight engineer, operates the NA1SS ham radio station in the Zvezda Service Module of the International Space Station. Equipment is a Kenwood TM-D700E transceiver.

Communication satellites called OSCARs (Orbiting Satellite Carrying Amateur Radio) can be accessed, some using a hand-held transceiver (HT), even, at times, using the factory “rubber duck” antenna.[15] Hams also use the moon, the aurora borealis, and the ionized trails of meteors as reflectors of radio waves.[16] Hams are also often able to make contact with the International Space Station (ISS),[17] as many astronauts and cosmonauts are licensed as amateur radio operators.[18]

Amateur radio operators use their amateur radio station to make contacts with individual hams as well as participating in round table discussion groups or “rag chew sessions” on the air. Some join in regularly scheduled on-air meetings with other amateur radio operators, called “nets” (as in “networks”) which are moderated by a station referred to as “Net Control”.[19] Nets can allow operators to learn procedures for emergencies, be an informal round table or be topical, covering specific interests shared by a group.

Licensing

The top of a tower supporting a yagi and several wire antennas

A handheld VHF/UHF transceiver

In all countries that license citizens to use amateur radio, operators are required to displaying knowledge and understanding of key concepts. This is usually done by passing an exam; however some authorities also recognize certain educational or professional qualifications (such as a degree in electrical engineering) in lieu.[20] In response, hams are granted operating privileges in larger segments of the radio frequency spectrum using a wide variety of communication techniques with higher power levels permitted compared to unlicensed personal radio services such as CB radio, Family Radio Service or PMR446 that require type-approved equipment restricted in frequency range and power.

In many countries, amateur licensing is a routine civil administrative matter. Amateurs are required to pass an examination to demonstrate technical knowledge, operating competence and awareness of legal and regulatory requirements in order to avoid interference with other amateurs and other radio services. There are often a series of exams available, each progressively more challenging and granting more privileges in terms of frequency availability, power output, permitted experimentation, and in some countries, distinctive call signs. Some countries such as the United Kingdom and Australia have begun requiring a practical training course in addition to the written exams in order to obtain a beginner’s license, called a Foundation License.

Amateur radio licensing in the United States serves as an example of the way some countries award different levels of amateur radio licenses based on technical knowledge. Three sequential levels of licensing exams (Technician Class, General Class and Amateur Extra Class) are currently offered, which allow operators who pass them access to larger portions of the Amateur Radio spectrum and more desirable call signs.

In some countries, an amateur radio license is necessary in order to purchase or possess amateur radio equipment.[21] An amateur radio license is only valid in the country in which it is issued, or in another country that has a reciprocal licensing agreement with the issuing country.

Both the requirements for and privileges granted to a licensee vary from country to country, but generally follow the international regulations and standards established by the International Telecommunications Union[22] and World Radio Conferences. In most countries, an individual will be assigned a call sign with their license. In some countries, a separate “station license” is required for any station used by an amateur radio operator. Amateur radio licenses may also be granted to organizations or clubs. Some countries only allow ham radio operators to operate club stations. Others, such as Syria and Cuba restrict all operation by foreigners to club stations only. Radio transmission permits are closely controlled by nations’ governments because clandestine uses of radio can be made, and, because radio waves propagate beyond national boundaries, radio is an international matter.

Licensing requirements

Prospective amateur radio operators are examined on understanding of the key concepts of electronics, radio equipment, antennas, radio propagation, RF safety, and the radio regulations of the government granting the license. These examinations are sets of questions typically posed in either a short answer or multiple-choice format. Examinations can be administered by bureaucrats, non-paid certified examiners, or previously licensed amateur radio operators.

The ease with which an individual can acquire an amateur radio license varies from country to country. In some countries, examinations may be offered only once or twice a year in the national capital, and can be inordinately bureaucratic (for example in India) or challenging because some amateurs must undergo difficult security approval (as in Iran). A handful of countries, currently only Yemen and North Korea, simply do not issue amateur radio licenses to their citizens, although in both cases a limited number of foreign visitors have been permitted to obtain amateur licenses in the past decade. Some developing countries, especially those in Africa, Asia, and Latin America, require the payment of annual license fees that can be prohibitively expensive for most of their citizens. A few small countries may not have a national licensing process and may instead require prospective amateur radio operators to take the licensing examinations of a foreign country. In countries with the largest numbers of amateur radio licensees, such as Japan, the United States, Canada, and most of the countries in Europe, there are frequent license examinations opportunities in major cities.

The granting of a separate license to a club or organization generally requires that an individual with a current and valid amateur radio license, who is in good standing with the telecommunications authority, assumes responsibility for any operations conducted under the club license or club call sign. A few countries may issue special licenses to novices or beginners that do not assign the individual a call sign, but require the newly-licensed individual to operate from stations licensed to a club or organization for a period of time before a higher class of license can be acquired.

Reciprocal licensing

Further information: Amateur radio international operation

A reciprocal licensing agreement between two countries allows bearers of an amateur radio license in one country under certain conditions to legally operate an amateur radio station in the other country without having to obtain an amateur radio license from the country being visited, or the bearer of a valid license in one country can receive a separate license and a call sign in another country, both of which have a mutually-agreed reciprocal licensing approvals. Reciprocal licensing requirements vary from country to country. Some countries have bilateral or multilateral reciprocal operating agreements allowing hams to operate within their borders with a single set of requirements. Some countries lack reciprocal licensing systems.

When traveling abroad, visiting amateur operators must follow the rules of the country in which they wish to operate. Some countries have reciprocal international operating agreements allowing hams from other countries to operate within their borders with just their home country license. Other host countries require that the visiting ham apply for a formal permit, or even a new host country-issued license, in advance.

The reciprocal recognition of licenses frequently not only depends on the involved licensing authorities, but also on the nationality of the bearer. As an example, in the US foreign licenses are only recognized if the bearer does not have US citizenship and holds no US license (which may differ in terms of operating privileges and restrictions). Conversely, a US citizen may operate under reciprocal agreements in Canada, but not a non-US citizen holding a US license.

Newcomers

Many people start their involvement in amateur radio by finding a local club. Clubs often provide information about licensing, local operating practices, and technical advice. Newcomers also often study independently by purchasing books or other materials, sometimes with the help of a mentor, teacher, or friend. Established amateurs who help newcomers are often referred to as “Elmers” within the ham community.[23][24] In addition, many countries have national amateur radio societies which encourage newcomers and work with government communications regulation authorities for the benefit of all radio amateurs. The oldest of these societies is the Wireless Institute of Australia, formed in 1910; other notable societies are the Radio Society of Great Britain, the American Radio Relay League, Radio Amateurs of Canada, the New Zealand Association of Radio Transmitters and South African Radio League. (See Category:Amateur radio organizations)

Call signs

Further information: ITU prefix – amateur and experimental stations

An amateur radio operator uses a call sign on the air to legally identify the operator or station.[25] In some countries, the call sign assigned to the station must always be used, whereas in other countries, the call sign of either the operator or the station may be used.[26] In certain jurisdictions, an operator may also select a “vanity” call sign although these must also conform to the issuing government’s allocation and structure used for Amateur Radio call signs.[27] Some jurisdictions, such as the U.S., require that a fee be paid to obtain such a vanity call sign; in others, such as the UK, a fee is not required and the vanity call sign may be selected when the license is applied for.

Call sign structure as prescribed by the ITU, consists of three parts which break down as follows, using the call sign ZS1NAT as an example:

  1. ZS – Shows the country from which the call sign originates and may also indicate the license class. (This call sign is licensed in South Africa, and is CEPT Class 1. Where specific classes of amateur radio license exist, the call signs may be assigned by class, but the specifics vary by issuing country.)
  2. 1 – Gives the subdivision of the country or territory indicated in the first part (this one refers to the Western Cape).
  3. NAT – The final part is unique to the holder of the license, identifying that station specifically.

Many countries do not follow the ITU convention for the numeral. In the United Kingdom the original calls G0xxx, G2xxx, G3xxx, G4xxx, were Full (A) License Holders along with the last M0xxx full call signs issued by the City & Guilds examination authority in December 2003. Additional full licenses were originally granted in respect of (B) Licensees with G1xxx, G6xxx, G7xxx, G8xxx and 1991 onward with M1xxx calls. The newer three level Intermediate licensees are 2E1xxx and 2E0xx and basic Foundation license holders are granted M3xxx, M6xxx call signs.[28] In the United States, for non-Vanity licenses, the numeral indicates the geographical district the holder resided in when the license was issued. Prior to 1978, US hams were required to obtain a new call sign if they moved out of their geographic district.

Also, for smaller entities, a numeral may be part of the country identification. For example, VP2xxx is in the British West Indies (subdivided into VP2Exx Anguilla, VP2Mxx Montserrat, and VP2Vxx British Virgin Islands), VP5xxx is in the Turks and Caicos Islands, VP6xxx is on Pitcairn Island, VP8xxx is in the Falklands, and VP9xxx is in Bermuda.

Online callbooks or callsign databases can be browsed or searched to find out who holds a specific callsign.[29] Non-exhaustive lists of famous people who hold or have held amateur radio callsigns have also been compiled and published.[30]

Many jurisdictions issue specialty vehicle registration plates to licensed amateur radio operators often in order to facilitate their movement during an emergency.[31][32] The fees for application and renewal are usually less than the standard rate for specialty plates.[31][33]

Privileges

In most administrations, unlike other RF spectrum users, radio amateurs may build or modify transmitting equipment for their own use within the amateur spectrum without the need to obtain government certification of the equipment.[34][35] Licensed amateurs can also use any frequency in their bands (rather than being allocated fixed frequencies or channels) and can operate medium to high-powered equipment on a wide range of frequencies[36] so long as they meet certain technical parameters including occupied bandwidth, power, and maintenance of spurious emission.

Radio amateurs have access to frequency allocations throughout the RF spectrum, enabling choice of frequency to enable effective communication whether across a city, a region, a country, a continent or the whole world regardless of season or time of day. The shortwave bands, or HF, can allow worldwide communication, the VHF and UHF bands offer excellent regional communication, and the broad microwave bands have enough space, or bandwidth, for television (known as amateur television (FSTV)) transmissions and high-speed computer networks.

The international symbol for amateur radio, included in the logos of many IARU member societies. The diamond holds a circuit diagram featuring components common to every radio: an antenna, inductor and ground.

In most countries, an amateur radio license grants permission to the license holder to own, modify, and operate equipment that is not certified by a governmental regulatory agency. This encourages amateur radio operators to experiment with home-constructed or modified equipment. The use of such equipment must still satisfy national and international standards on spurious emissions.

The amount of output power an amateur radio licensee may legally use varies from country to country. Although allowable power levels are moderate by commercial standards, they are sufficient to enable global communication. Power limits vary from country to country and between license classes within a country. For example, the peak envelope power limits for the highest available license classes in a few selected countries are: 2.25 kW in Canada, was 2 kW in the former Yugoslavia, 1.5 kW in the United States, 1 kW in Belgium and Switzerland, 750 W in Germany, 500 W in Italy, 400 W in Australia, India and the United Kingdom, and 150 W in Oman. Lower license classes usually have lower power limits; for example, the lowest license class in the UK has a limit of 10 W. Amateur radio operators are encouraged both by regulations and tradition of respectful use of the spectrum to use as little power as possible to accomplish the communication.[37] Output power may also depend on the mode of transmission. In Australia, for example, although 400w Peak Envelope Power may be used for SSB transmissions, FM and other modes are limited to 120 watts.

Band plans and frequency allocations

Main article: Amateur radio frequency allocations

The International Telecommunication Union (ITU) governs the allocation of communications frequencies worldwide, with participation by each nation’s communications regulation authority. National communications regulators have some liberty to restrict access to these bandplan frequencies or to award additional allocations as long as radio services in other countries do not suffer interference. In some countries, specific emission types are restricted to certain parts of the radio spectrum, and in most other countries, International Amateur Radio Union (IARU) member societies adopt voluntary plans to ensure the most effective use of spectrum.

In a few cases, a national telecommunication agency may also allow hams to use frequencies outside of the internationally allocated amateur radio bands. In Trinidad and Tobago, hams are allowed to use a repeater which is located on 148.800 MHz. This repeater is used and maintained by the National Emergency Management Agency (NEMA), but may be used by radio amateurs in times of emergency or during normal times to test their capability and conduct emergency drills. This repeater can also be used by non-ham NEMA staff and REACT members. In Australia and New Zealand ham operators are authorized to use one of the UHF TV channels. In the U.S., in cases of emergency, amateur radio operators providing essential communication needs in connection with the immediate safety of human life and immediate protection of property when normal communication systems are not available may use any frequency including those of other radio services such as police and fire communications[citation needed] and the Alaska statewide emergency frequency of 5167.5 kHz.

Similarly, amateurs in the United States may apply to be registered with the Military Auxiliary Radio System (MARS). Once approved and trained, these amateurs also operate on US government military frequencies to provide contingency communications and morale message traffic support to the military services.

Equipment

Modes of communication

Amateurs use a variety of voice, text, image and data communications modes over radio. Generally new modes can be tested in the amateur radio service, although national regulations may require disclosure of a new mode to permit radio licensing authorities to monitor the transmissions. Encryption, for example, is not generally permitted in the Amateur Radio service except for the special purpose of satellite vehicle control uplinks. The following is a partial list of the modes of communication used, where the mode includes both modulation types and operating protocols.

Voice

  • Amplitude Modulation (AM)
  • Double Sideband Suppressed Carrier (DSB-SC)
  • Independent Sideband (ISB)
  • Single Sideband (SSB)
  • Amplitude Modulation Equivalent (AME)
  • Frequency Modulation (FM)
  • Phase Modulation (PM)

Image

  • Amateur Television, also known as Fast Scan television (ATV)
  • Slow Scan Television (SSTV)
  • Facsimile

Text and data

Most amateur digital modes are transmitted by inserting audio into the microphone input of a radio and using an analog scheme, such as amplitude modulation (AM), frequency modulation (FM), or single-sideband modulation (SSB).

  • Continuous Wave (CW)
  • ALE Automatic Link Establishment
  • AMateur Teleprinting Over Radio (AMTOR)
  • D-Star
  • Echolink
  • Hellschreiber, also referred to as either Feld-Hell, or Hell
  • Discrete multi-tone modulation modes such as Multi Tone 63 (MT63)
  • Multiple Frequency-Shift Keying (MFSK)modes such as
    • FSK441, JT6M, JT65, and
    • Olivia MFSK
  • Packet Radio (AX25)
  • Automatic Packet Reporting System (APRS)
  • PACTOR
  • Phase Shift Keying
    • 31 baud binary phase shift keying: PSK31
    • 31 baud quadrature phase shift keying: QPSK31
    • 63 baud binary phase shift keying: PSK63
    • 63 baud quadrature phase shift keying: QPSK63
  • Spread spectrum
  • Simplex Teletype Over Radio (SITOR)
  • Radio Teletype (RTTY)
  • 8FSK 8ary Frequency Shift Keying

Modes by activity

The following ‘modes’ use no one specific modulation scheme but rather are classified by the activity of the communication.

  • Earth-Moon-Earth (EME)
  • Internet Radio Linking Project (IRLP)
  • Low Transmitter Power (QRP)
  • Satellite (OSCAR)
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AL-572Y HF AMP, 1300W, (4) 572B TUBES, 100/110/120V,EXPORT
AL-572YQ HF AMP, 1300W, (4) 572B, QSK, 100/110/120V, EXPORT
AL-800 HF AMPLIFIER, 1.25 KW, 800 TUBE
AL-800F HF AMPLIFIER, 1.25 KW, IMPORT 3CX800A7 TUBE
AL-800H HF AMPLIFIER, 1.5 KW+, 2 X 800 TUBES
AL-800HF HF AMPLIFIER, 1.5 KW+, IMPORTED TUBE 2X 3CX800A7
AL-800HX HF AMPLIFIER, 1.5 KW+, 2X800 TUBES, EXPORT
AL-800HXCE HF AMPLIFIER, 1.5 KW+, 2X800 TUBES, EXPORT, CE
AL-800X HF AMPLIFIER, 1.25KW, 800 TUBE, EXPORT
AL-800XCE HF AMPLIFIER, 1.25KW, 800 TUBE, EXPORT, CE
AL-80B HF AMP, 1KW, (1) 3-500Z TUBES, DOMESTIC 120VAC
AL-80BQ 1.5 KW OUTPUT, 3-500Z,100/110/120V,QSK5PC INSTALLE
AL-80BX AMPLIFIER, 1KW, ONE 3-500Z TUBE, EXPORT
AL-80BXCE AMPLIFIER, 1KW, ONE 3-500Z TUBE, EXPORT, CE
AL-80BXQ AMPLIFIER, 1.5KW OUTPUT,3-500Z, 200/220/240V QSK5P
AL-80BXQCE AMPLIFIER, 1.5KW OUTPUT,3-500Z, QSK, 240V CE
AL-80BY AMPLIFIER, 1KW, ONE 3-500Z TUBE, EXPORT,100/110/12
AL-80BYQ AMPLIFIER, TWO 3-500Z, 100/110/120V QSK-5PC INST.
AL-811 HF AMP, 600W, (3) 811A TUBES
AL-811H HF AMP, 800W, (4) 811A TUBES, US 120VAC
AL-811HD HF AMP, 800W, (4) 572B TUBES, US 120VAC
AL-811HDX HF AMP, 800W, (4) 572B TUBES, EXPORT, 220VAC
AL-811HDXCE HF AMP, 800W, (4)572B, EXPORT/CE, 220VAC
AL-811HDY HF AMP, 800W, (4)572B, EXPORT, W/10M, 110VAC
AL-811HX HF AMP, 800W, (4) 811A TUBES, EXPORT 240VAC
AL-811HXCE HF AMP, 800W, (4) 811A TUBES, EXPORT 240VAC, CE
AL-811HY HF AMP, 800W, (4) 811A TUBES, EXPORT, 120VAC
AL-811X HF AMP, 600W, (3) 811A TUBES, EXPORT, 240VAC
AL-811XCE HF AMP, 600W, CE,(3)811A TUBES, EXPORT, 240VAC
AL-811Y EXPORT MODEL, INCLUDES 10 METERS, 100/110/120V
AL-82 AMPLIFIER, TWO 3-500Z
AL-82J JAPANESE MODEL, INCLUDES 10 METERS, 200V
AL-82JQ AMPLIFIER, TWO 3-500Z, WITH PIN-5 INSTALL
AL-82Q AMPLIFIER, TWO 3-500Z, WITH PIN-5 INSTALL
AL-82X AMPLIFIER, 1500W, EXPORT, TWO 3-500Z
AL-82XCE AMPLIFIER, 1500W, EXPORT, CE, TWO 3-500Z
AL-82XQ AMPLIFIER, TWO 3-500Z , EXPORT WITH PIN-5 INSTALL
AL-82XQCE AMPLIFIER, TWO 3-500Z, QSK, EXPORT, CE
ALS-1300 HF AMP, 1200 WATT SOLID STATE
ALS-1300X HF AMP, 1200 WATT SOLID STATE, EXPORT W/10METER
ALS-500M MOBILE AMP, 500W SOLID STATE, REMOTE READY, 12V US
ALS-500MR MOBILE AMP, REMOTE COMBO, 500W, 12 VD, US
ALS-500MRX MOBILE AMP, REMOTE COMBO, 500W, 12V, EXPORT
ALS-500MRXCE MOBILE AMP, REMOTE COMBO, 500W, 12V, EXPORT,CE
ALS-500MX 500 WATTS, SOLID STATE, MOBILE, 13.8V, EXPORT
ALS-500MXCE 500 WATT, MOBILE, SOLID STATE, 13.8 VDC, EXPORT,CE
ALS-600 600 WATT SOLID STATE AMP
ALS-600S 600 WATT SOLID STATE AMP W/SWITCHING PS
ALS-600SX 600 WATT SOLID STATE AMP W/SWITCHING PS EXPORT
ALS-600X 600 WATT SOLID STATE AMP EXPORT VERS.
ALS-600Y 600 WATT SOLID STATE AMP, EXPORT

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Category : Amateur Radio Amplifier Repair Service | HAM Radio Amplifier Repair | Industrial Repair Group | Industrial Repair Service | Linear Amplifier Repair | Blog
7
Sep

Service

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Dexter Laundry VFD - Delta DTR015S21A

Troubleshooting a Dexter Laundry VFD / Inverter Drive F13 Fault Code ( F13 Error Code)

If you receive an F13 Fault Code (Communication Error Code) on the FRONT washer computer display,  remove the rear inspection plate covering the Variable Frequency Drive VFD.

Step 1: Turn power off to the washer, it must remain off for three minutes for drive to reset. The washer will not operate correctly if this is done improperly. This will allow most fault codes to reset that are displayed at washer front.

Step 2: Power on the washer and wait a few minutes for the machine to power up.

Step 3: Check the washer computer display for faults codes. If you receive an F13 fault code, then you should proceed to check the Variable Frequency Drive VFD display in the rear of the machine. In normal standby mode the Variable Frequency Drive VFD Display should read “F  0.0”.

If your Dexter VFD display (viewed from rear panel removed) appears scrambled, unreadable, or has a dim display; a Dexter VFD Repair from Industrial Repair Group is likely needed. Please don't hesitate to request a FAST REPAIR QUOTE  from Industrial Repair Group. 

If the Dexter VFD Drive displays F 0.0 then follow the steps below:

Check the data communication cable between the washer computer and the variable frequency drive (VFD).

Step 4: Make sure the cable did not become unplugged during operation.

Step 5: Make sure that the cable is not being pulled sideways at either the washer controller, or the VFD, plug end. If both ends of the communications cable are plugged in the washer computer and VFD and there is no tension on the communications cable pulling it from side to side, then replace the cable.

Step 6: Inspect both female connection points at PCB controller and at Variable Frequency Drive VFD.

Industrial Repair Group repairs all Dexter Laundry VFD Drives / Inverter Drives  - Delta Electronics (DTR007S11A, DTR007S21U, DTR015S21U, DTR015S21U3, DTR015S21A, DTR022S21U, DTR022S21A)

Industrial Repair Group performs extensive Dexter VFD Repair (Inverter Drive) F13 Error Code / Fault Code at the component level, touching up solder traces, replacing bad components, as well as full testing of ICs, PALs, EPROMs, GALs, surface mounted components and much more. Every Dexter VFD Repair (Inverter Drive) F13 Error Code / Fault Code is subjected to dynamic function tests to verify successful repair and then backed by our 18 month repair guarantee. Sealers and conformal coatings are re-applied as needed with each repair restoring your equipment back to its original OEM specs.

INDUSTRIAL REPAIR GROUP FAST QUOTE

Request a Fast Quote

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Get a Repair Fast Quote Now for your Dexter VFD Repair (Inverter Drive) F13 Error Code / Fault Code

Industrial Repair Group prides ourselves on giving accurate quotes. Rest assured that our first price quote is our only price quote. Our mission statement is simple: IRG will get the job done as promised and on schedule, our customers will be satisfied, and all repairs will be backed with our 18 month repair guarantee!

Service Guarantee

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At Industrial Repair Group, our goal is to offer the best repair in the industry and the most competitive quotes. Our wide selection of services and industry leading 18 month repair guarantee are sure to provide you with the perfect repair solution for all of your industrial needs. We specialize in industrial electronics, electric motor rebuilds, and complete customer satisfaction.

ALL INDUSTRIAL REPAIR GROUP REPAIRS COME WITH AN 18 MONTH REPAIR GUARANTEE!

Summary of Warranty

Industrial Repair Group LLC. warrants to you, the ORIGINAL PURCHASER and ANY SUBSEQUENT OWNER of each Industrial Repair Group repair, for a period of one (1) year and six (6) months from the date of the repair (the "warranty period") that Industrial Repair Group's service is free of defects in materials and workmanship. We further warrant the repair regardless of the reason for failure, except as excluded in this Warranty.

Items Excluded From This Warranty

This Warranty is in effect only for failure of a Industrial Repair Group repair which occurred within the Warranty Period. It does not cover any product which has been damaged because of any intentional misuse, accident, negligence, ordinary wear and tear, cosmetic damage, or loss which is covered under any of your insurance contracts. The Industrial Repair Group Warranty also does not extend to the repaired products if the Industrial Repair Group LLC asset control number has been defaced, altered, or removed.

What Industrial Repair Group Will Do

We will remedy any defect, regardless of the reason for failure (except as excluded), by repair, replacement, or refund. We may not elect refund unless you agree, or unless we are unable to provide replacement, and repair is not practical or cannot be timely made. If a refund is elected, then you must make the defective or malfunctioning product available to us free and clear of all liens or other encumbrances. The refund will be equal to the actual repair price, not including interest, insurance, closing costs, and other finance charges less a reasonable depreciation on the product from the date of repair. Warranty work can only be performed at our fulfillment center. We will remedy the defect and ship the product from the service center within a reasonable time after receipt of the defective product. All expenses in remedying the defect, including surface shipping costs in the United States, will be borne by us. (You must bear the expense of shipping the product between any foreign country and the port of entry in the United States including the return shipment, and all taxes, duties, and other customs fees for such foreign shipments.)

How to Obtain Warranty Service

You must notify us of your need for warranty service within the warranty period. All components must be shipped in a factory pack, which, if needed, may be obtained from us free of charge. Corrective action will be taken within a reasonable time of the date of receipt of the defective product by us or our authorized service center. If the repairs made by us or our authorized service center are not satisfactory, notify us or our authorized service center immediately.

Disclaimer of Consequential and Incidental Damages.

You are not entitled to recover from us any incidental damages resulting from any defect in the Industrial Repair Group repair service. This includes any damage to another product or products resulting from such a defect.

Warranty Alterations

No person has the authority to enlarge, amend, or modify this Warranty. This Warranty is not extended by the length of time which you are deprived of the use of your equipment. Repairs and replacement parts provided under the terms of this IRG Warranty shall carry only the unexpired portion of this Industrial Repair Group Warranty.

How Variable Freq. Drives Work

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Thank you for choosing Industrial Repair Group. If you would like a printable version of How Variable Frequency Drives Operate, please follow this link: IRG-Variable-Frequency-Drive

How Variable-Frequency Drives Operate

A variable-frequency drive (VFD) is a system for controlling the rotational speed of an alternating current (AC) electric motor by controlling the frequency of the electrical power supplied to the motor.[1][2][3] A variable frequency drive is a specific type of adjustable-speed drive. Variable-frequency drives are also known as adjustable-frequency drives (AFD), variable-speed drives (VSD), AC drives, microdrives or inverter drives. Since the voltage is varied along with frequency, these are sometimes also called VVVF (variable voltage variable frequency) drives.

Variable-frequency drives are widely used. In ventilation systems for large buildings, variable-frequency motors on fans save energy by allowing the volume of air moved to match the system demand. They are also used on pumps, elevator, conveyor and machine tool drives.

VFD types

All VFDs use their output devices (IGBTs, transistors, thyristors) only as switches, turning them only on or off. Using a linear device such as a transistor in its linear mode is impractical for a VFD drive, since the power dissipated in the drive devices would be about as much as the power delivered to the load.

Drives can be classified as:

  • Constant voltage
  • Constant current
  • Cycloconverter

In a constant voltage converter, the intermediate DC link voltage remains approximately constant during each output cycle. In constant current drives, a large inductor is placed between the input rectifier and the output bridge, so the current delivered is nearly constant. A cycloconverter has no input rectifier or DC link and instead connects each output terminal to the appropriate input phase.

The most common type of packaged VF drive is the constant-voltage type, using pulse width modulation to control both the frequency and effective voltage applied to the motor load.

VFD system description

VFD system

A variable frequency drive system generally consists of an AC motor, a controller and an operator interface.[4][5]

VFD motor

The motor used in a VFD system is usually a three-phase induction motor. Some types of single-phase motors can be used, but three-phase motors are usually preferred. Various types of synchronous motors offer advantages in some situations, but induction motors are suitable for most purposes and are generally the most economical choice. Motors that are designed for fixed-speed operation are often used. Certain enhancements to the standard motor designs offer higher reliability and better VFD performance, such as MG-31 rated motors.[6]

VFD controller

Variable frequency drive controllers are solid state electronic power conversion devices. The usual design first converts AC input power to DC intermediate power using a rectifier or converter bridge. The rectifier is usually a three-phase, full-wave-diode bridge. The DC intermediate power is then converted to quasi-sinusoidal AC power using an inverter switching circuit. The inverter circuit is probably the most important section of the VFD, changing DC energy into three channels of AC energy that can be used by an AC motor. These units provide improved power factor, less harmonic distortion, and low sensitivity to the incoming phase sequencing than older phase controlled converter VFD’s. Since incoming power is converted to DC, many units will accept single-phase as well as three-phase input power (acting as a phase converter as well as a speed controller); however the unit must be derated when using single phase input as only part of the rectifier bridge is carrying the connected load.[7]

As new types of semiconductor switches have been introduced, these have promptly been applied to inverter circuits at all voltage and current ratings for which suitable devices are available. Introduced in the 1980s, the insulated-gate bipolar transistor (IGBT) became the device used in most VFD inverter circuits in the first decade of the 21st century.[8][9][10]

AC motor characteristics require the applied voltage to be proportionally adjusted whenever the frequency is changed in order to deliver the rated torque. For example, if a motor is designed to operate at 460 volts at 60 Hz, the applied voltage must be reduced to 230 volts when the frequency is reduced to 30 Hz. Thus the ratio of volts per hertz must be regulated to a constant value (460/60 = 7.67 V/Hz in this case). For optimum performance, some further voltage adjustment may be necessary especially at low speeds, but constant volts per hertz is the general rule. This ratio can be changed in order to change the torque delivered by the motor.[11]

In addition to this simple volts per hertz control more advanced control methods such as vector control and direct torque control (DTC) exist. These methods adjust the motor voltage in such a way that the magnetic flux and mechanical torque of the motor can be precisely controlled.

The usual method used to achieve variable motor voltage is pulse-width modulation (PWM). With PWM voltage control, the inverter switches are used to construct a quasi-sinusoidal output waveform by a series of narrow voltage pulses with pseudosinusoidal varying pulse durations.[8][12]

Operation of the motors above rated name plate speed (base speed) is possible, but is limited to conditions that do not require more power than nameplate rating of the motor. This is sometimes called “field weakening” and, for AC motors, means operating at less than rated volts/hertz and above rated name plate speed. Permanent magnet synchronous motors have quite limited field weakening speed range due to the constant magnet flux linkage. Wound rotor synchronous motors and induction motors have much wider speed range. For example, a 100 hp, 460 V, 60 Hz, 1775 RPM (4 pole) induction motor supplied with 460 V, 75 Hz (6.134 V/Hz), would be limited to 60/75 = 80% torque at 125% speed (2218.75 RPM) = 100% power.[13] At higher speeds the induction motor torque has to be limited further due to the lowering of the breakaway torque of the motor. Thus rated power can be typically produced only up to 130…150 % of the rated name plate speed. Wound rotor synchronous motors can be run even higher speeds. In rolling mill drives often 200…300 % of the base speed is used. Naturally the mechanical strength of the rotor and lifetime of the bearings is also limiting the maximum speed of the motor. It is recommended to consult the motor manufacturer if more than 150 % speed is required by the application.

PWM VFD Output Voltage Waveform

An embedded microprocessor governs the overall operation of the VFD controller. The main microprocessor programming is in firmware that is inaccessible to the VFD user. However, some degree of configuration programming and parameter adjustment is usually provided so that the user can customize the VFD controller to suit specific motor and driven equipment requirements.[8]

VFD operator interface

The operator interface provides a means for an operator to start and stop the motor and adjust the operating speed. Additional operator control functions might include reversing and switching between manual speed adjustment and automatic control from an external process control signal. The operator interface often includes an alphanumeric display and/or indication lights and meters to provide information about the operation of the drive. An operator interface keypad and display unit is often provided on the front of the VFD controller as shown in the photograph above. The keypad display can often be cable-connected and mounted a short distance from the VFD controller. Most are also provided with input and output (I/O) terminals for connecting pushbuttons, switches and other operator interface devices or control signals. A serial communications port is also often available to allow the VFD to be configured, adjusted, monitored and controlled using a computer.[8][14][15]

VFD operation

When an induction motor is connected to a full voltage supply, it draws several times (up to about 6 times) its rated current. As the load accelerates, the available torque usually drops a little and then rises to a peak while the current remains very high until the motor approaches full speed.

By contrast, when a VFD starts a motor, it initially applies a low frequency and voltage to the motor. The starting frequency is typically 2 Hz or less. Thus starting at such a low frequency avoids the high inrush current that occurs when a motor is started by simply applying the utility (mains) voltage by turning on a switch. After the start of the VFD, the applied frequency and voltage are increased at a controlled rate or ramped up to accelerate the load without drawing excessive current. This starting method typically allows a motor to develop 150% of its rated torque while the VFD is drawing less than 50% of its rated current from the mains in the low speed range. A VFD can be adjusted to produce a steady 150% starting torque from standstill right up to full speed.[16] Note, however, that cooling of the motor is usually not good in the low speed range. Thus running at low speeds even with rated torque for long periods is not possible due to overheating of the motor. If continuous operation with high torque is required in low speeds an external fan is usually needed. The manufacturer of the motor and/or the VFD should specify the cooling requirements for this mode of operation.

In principle, the current on the motor side is in direct proportion of the torque that is generated and the voltage on the motor is in direct proportion of the actual speed, while on the network side, the voltage is constant, thus the current on line side is in direct proportion of the power drawn by the motor, that is U.I or C.N where C is torque and N the speed of the motor (we shall consider losses as well, neglected in this explanation).

(1) n stands for network (grid) and m for motor

(2) C stands for torque [Nm], U for voltage [V], I for current [A], and N for speed [rad/s]

We neglect losses for the moment :

Un.In = Um.Im (same power drawn from network and from motor)

Um.Im = Cm.Nm (motor mechanical power = motor electrical power)

Given Un is a constant (network voltage) we conclude : In = Cm.Nm/Un That is “line current (network) is in direct proportion of motor power”.

With a VFD, the stopping sequence is just the opposite as the starting sequence. The frequency and voltage applied to the motor are ramped down at a controlled rate. When the frequency approaches zero, the motor is shut off. A small amount of braking torque is available to help decelerate the load a little faster than it would stop if the motor were simply switched off and allowed to coast. Additional braking torque can be obtained by adding a braking circuit (resistor controlled by a transistor) to dissipate the braking energy. With 4-quadrants rectifiers (active-front-end), the VFD is able to brake the load by applying a reverse torque and reverting the energy back to the network.

Power line harmonics

While PWM allows for nearly sinusoidal currents to be applied to a motor load, the diode rectifier of the VFD takes roughly square-wave current pulses out of the AC grid, creating harmonic distortion in the power line voltage. When the VFD load size is small and the available utility power is large, the effects of VFD systems slicing small chunks out of AC grid generally go unnoticed. Further, in low voltage networks the harmonics caused by single phase equipment such as computers and TVs are such that they are partially cancelled by three-phase diode bridge harmonics.

However, when either a large number of low-current VFDs, or just a few very large-load VFDs are used, they can have a cumulative negative impact on the AC voltages available to other utility customers in the same grid.

When the utility voltage becomes misshapen and distorted the losses in other loads such as normal AC motors are increased. This may in the worst case lead to overheating and shorter operation life. Also substation transformers and compensation capacitors are affected, the latter especially if resonances are aroused by the harmonics.

In order to limit the voltage distortion the owner of the VFDs may be required to install filtering equipment to smooth out the irregular waveform. Alternately, the utility may choose to install filtering equipment of its own at substations affected by the large amount of VFD equipment being used. In high power installations decrease of the harmonics can be obtained by supplying the VSDs from transformers that have different phase shift.[17]

Further, it is possible to use instead of the diode rectifier a similar transistor circuit that is used to control the motor. This kind of rectifier is called active infeed converter in IEC standards. However, manufacturers call it by several names such as active rectifier, ISU (IGBT Supply Unit), AFE (Active Front End) or four quadrant rectifier. With PWM control of the transistors and filter inductors in the supply lines the AC current can be made nearly sinusoidal. Even better attenuation of the harmonics can be obtained by using an LCL (inductor-capacitor-inductor) filter instead of single three-phase filter inductor.

Additional advantage of the active infeed converter over the diode bridge is its ability to feed back the energy from the DC side to the AC grid. Thus no braking resistor is needed and the efficiency of the drive is improved if the drive is frequently required to brake the motor.

Application considerations

The output voltage of a PWM VFD consists of a train of pulses switched at the carrier frequency. Because of the rapid rise time of these pulses, transmission line effects of the cable between the drive and motor must be considered. Since the transmission-line impedance of the cable and motor are different, pulses tend to reflect back from the motor terminals into the cable. The resulting voltages can produce up to twice the rated line voltage for long cable runs, putting high stress on the cable and motor winding and eventual insulation failure. Increasing the cable or motor size/type for long runs and 480v or 600v motors will help offset the stresses imposed upon the equipment due to the VFD (modern 230v single phase motors not effected). At 460 V, the maximum recommended cable distances between VFDs and motors can vary by a factor of 2.5:1. The longer cables distances are allowed at the lower Carrier Switching Frequencies (CSF) of 2.5 kHz. The lower CSF can produce audible noise at the motors. For applications requiring long motor cables VSD manufacturers usually offer du/dt filters that decrease the steepness of the pulses. For very long cables or old motors with insufficient winding insulation more efficient sinus filter is recommended. Expect the older motor’s life to shorten. Purchase VFD rated motors for the application.

Further, the rapid rise time of the pulses may cause trouble with the motor bearings. The stray capacitance of the windings provide paths for high frequency currents that close through the bearings. If the voltage between the shaft and the shield of the motor exceeds few volts the stored charge is discharged as a small spark. Repeated sparking causes erosion in the bearing surface that can be seen as fluting pattern. In order to prevent sparking the motor cable should provide a low impedance return path from the motor frame back to the inverter. Thus it is essential to use a cable designed to be used with VSDs.[18]

In big motors a slip ring with brush can be used to provide a bypass path for the bearing currents. Alternatively isolated bearings can be used.

The 2.5 kHz and 5 kHz CSFs cause fewer motor bearing problems than the 20 kHz CSFs.[19] Shorter cables are recommended at the higher CSF of 20 kHz. The minimum CSF for synchronize tracking of multiple conveyors is 8 kHz.

The high frequency current ripple in the motor cables may also cause interference with other cabling in the building. This is another reason to use a motor cable designed for VSDs that has a symmetrical three-phase structure and good shielding. Further, it is highly recommended to route the motor cables as far away from signal cables as possible.[20]

Available VFD power ratings

Variable frequency drives are available with voltage and current ratings to match the majority of 3-phase motors that are manufactured for operation from utility (mains) power. VFD controllers designed to operate at 111 V to 690 V are often classified as low voltage units. Low voltage units are typically designed for use with motors rated to deliver 0.2 kW or 1/4 horsepower (hp) up to several megawatts. For example, the largest ABB ACS800 single drives are rated for 5.6 MW[21] . Medium voltage VFD controllers are designed to operate at 2,400/4,162 V (60 Hz), 3,000 V (50 Hz) or up to 10 kV. In some applications a step up transformer is placed between a low voltage drive and a medium voltage load. Medium voltage units are typically designed for use with motors rated to deliver 375 kW or 500 hp and above. Medium voltage drives rated above 7 kV and 5,000 or 10,000 hp should probably be considered to be one-of-a-kind (one-off) designs.[22]

Medium voltage drives are generally rated amongst the following voltages : 2,3 KV – 3,3 Kv – 4 Kv – 6 Kv – 11 Kv

The in-between voltages are generally possible as well. The power of MV drives is generally in the range of 0,3 to 100 MW however involving a range a several different type of drives with different technologies.

Dynamic braking

Using the motor as a generator to absorb energy from the system is called dynamic braking. Dynamic braking stops the system more quickly than coasting. Since dynamic braking requires relative motion of the motor’s parts, it becomes less effective at low speed and cannot be used to hold a load at a stopped position. During normal braking of an electric motor the electrical energy produced by the motor is dissipated as heat inside of the rotor, which increases the likelihood of damage and eventual failure. Therefore, some systems transfer this energy to an outside bank of resistors. Cooling fans may be used to protect the resistors from damage. Modern systems have thermal monitoring, so if the temperature of the bank becomes excessive, it will be switched off.[23]

Regenerative variable-frequency drives

Regenerative AC drives have the capacity to recover the braking energy of an overhauling load and return it to the power system.[24]

Line regenerative variable frequency drives, showing capacitors(top cylinders)and inductors attached which filter the regenerated power.

[2][3][24][25][26][27]

Cycloconverters and current-source inverters inherently allow return of energy from the load to the line; voltage-source inverters require an additional converter to return energy to the supply.[28]

Regeneration is only useful in variable-frequency drives where the value of the recovered energy is large compared to the extra cost of a regenerative system,[28] and if the system requires frequent braking and starting. An example would be use in conveyor belt during manufacturing where it should stop for every few minutes, so that the parts can be assembled correctly and moves on. Another example is a crane, where the hoist motor stops and reverses frequently, and braking is required to slow the load during lowering. Regenerative variable-frequency drives are widely used where speed control of overhauling loads is required.

Brushless DC motor drives

Much of the same logic contained in large, powerful VFDs is also embedded in small brushless DC motors such as those commonly used in computer fans. In this case, the chopper usually converts a low DC voltage (such as 12 volts) to the three-phase current used to drive the electromagnets that turn the permanent magnet rotor.

See also

  • Regenerative variable-Frequency drives
  • Direct torque control
  • Frequency changer
  • Space Vector Modulation
  • Variable speed air compressor
  • Vector control (motor)
DTR007S11A
DTR007S21U
DTR015S21U
DTR015S21U3
DTR015S21A
DTR022S21U
DTR022S21A
Category : AC Drive Repair | DC Drive Repair | Dexter VFD Repair | Electronic Repair Services | Industrial Controls Repair | VFD Drive Repair | VFD Drives | Blog