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Frequency Convertors FAQ


A frequency changer or frequency converter is an electronic (solid-state) or electromechanical (motor-generator set) device that converts alternating current (AC) of one frequency to alternating current of another frequency. The device may also change the voltage, but if it does, that is incidental to its principal purpose, since voltage conversion of alternating current is much easier to achieve than frequency conversion.

Traditionally, these devices were electromechanical machines (motor-generator sets). With the advent of solid-state electronics, it has become possible to build completely electronic frequency changers. These devices usually consist of a rectifier stage (producing direct current) which is then inverted to produce AC of the desired frequency. The inverter may use thyristors or IGBTs. If voltage conversion is desired, a transformer will usually be included in either the AC input or output circuitry and this transformer may also provide galvanic isolation between the input and output AC circuits.

Rotary frequency converter units use input power to run a motor, which produces mechanical energy to spin a generator, which in turn produces the required output power. Solid state frequency converter units convert incoming AC power into DC, and then convert the DC into the required output power.

A phase converter is a device that converts electric power provided as a single-phase to simulated three phases. The majority of phase converters are used to produce three-phase electric power from a single-phase source, thus allowing the operation of three-phase equipment at a site that only has single-phase electrical service. Phase converters are used where a three-phase service is not available from the utility or is too costly to install due to a remote location. A utility will generally charge a higher fee for a three-phase service because of the extra equipment, including transformers, metering, and distribution wire.

The quality of the three-phase output is poor but good enough to run a motor load. Since motors above 10 HP tend it be 3 phase only, phase converters are often used to drive larger motor loads.  

Phase converters can be rotary mechanical devices or solid-state (electronic) devices.

In the same way that 400 Hz power allows for denser power, the need for denser 60 Hz (or 50 Hz) power leads to the use of Three Phase (3ɸ) power for a variety of industry needs.  In three-phase line conditioners, three single-phase power waves are combined, with the second wave 120 degrees ahead of the first wave, and the third wave 240 degrees ahead of the first wave.

Rotary frequency converters (also called "Motor-Generators" or MG Sets") convert incoming AC Power into rotary mechanical power (spinning motor), which transmits its rotary power to a generator, which converts its mechanical power into Electric AC output power. Rotary power is often described in terms of Horsepower, while Electrical power is described in Kilowatts (kW) or Kilovolt-Amperes (KVA). The conversion of frequency (hertz – Hz), voltage, and/or phase (3 phase, 1 phase) are inherent in this process.

Motor Generator sets use several methods of coupling the drive motor to the generator. The simplest and least expensive method is belt coupled converters that use drive belts and pulleys to not only transfer the energy from motor to generator, but also change the frequency by pulley ratio. Some clients are concerned with the longevity of drive belts, but in practice, drive belts do not fail when properly designed and installed.  Georator has a flawless record in that regard.

Another method is direct coupled converters that directly couple the motor shaft to the generator shaft using a mechanical coupling, and adjusting the speed of the drive motor to vary the rotational speed of the generator, thus varying the output frequency. An adjustable speed electronic drive (ASD) is used for this purpose, instead of a conventional motor starter.

Finally, the most sophisticated and most costly method is to build the motor and generator onto a single common shaft, called common shaft frequency converters. In this case, the frequency change is made by winding the motor with a different number of electrical poles than the generator. For example, a 12 pole motor and 10 pole generator will yield a 60-to-50 Hz conversion.

In certain applications, only power line isolation (complete electrical discontinuity, input to output) or power line conditioning (poor incoming electrical power converted to good output power), is required. In these power line isolators, an insulated flexible coupling is used between motor and generator, to transmit the power from motor to generator, and completely isolate the input from the output. Typically, no change is made to the frequencies, although phase or voltage conversion may be required.

A frequency inverter is often confused with a frequency converter since both appear to change output voltage, frequency and amperage.  The frequency inverter, also called an adjustable speed drive (ASD) or a variable frequency drive (VFD) is used to vary the speed, power, and torque of a connected induction motor to meet required load conditions.

The primary difference between the two technologies is that the inverter section in a converter attempts to maintain consistent voltage and frequency output regardless of current output.  The adjustable speed drive varies the voltage and frequency with generally consistent current output to speed up or slow down a motor load.  Frequency inverters are typically rated in terms of maximum current output, while frequency converters are rated in terms of power output.  In many cased, the “quality” of the output, as measured by “distortion” of the sine wave output, is better in the converters, since that precision is not requires in adjustable speed drives.

Power line conditioners (also known as line conditioners or powerline battery isolators) are a device intended to improve the quality of the power that is delivered to electrical load equipment. While there is no official definition of a power line conditioner, the term most often refers to a device that acts in one or more ways to deliver a voltage of the proper level and characteristics to enable load equipment to function properly. In a nutshell, poor incoming electrical power converted to good output power.

Rotary frequency converters are very good at starting and running typical factory loads. They have the ability to produce high starting surge currents for short periods, making them ideal for motor loads. These converters are very robust, and can tolerate harsh environments. While they are susceptible to driving rain, with the proper enclosures these units can be placed outdoors, and tolerate a wide range of operating temperature environments.

A short answer:

Solid state frequency converters are ideal where noise, size, precision or adjustability are paramount. 

A long answer:

Solid state frequency converters are inherently quiet, much like computers, with the main “noise” coming from forced air cooling fans.  This makes solid state units ideal for office and laboratory environments.  Also, solid state circuitry lends itself to precision and accuracy, limited only by the amount of expense the client wishes to spend on the subject.

Typical limits on these issues are noise levels less than or equal to 65 decibels (dB), and accuracies well within the 1% range for all meaningful parameters.

Solid-state frequency converters are not very good at starting motor loads because of the typical motor starting surge current required to start motors.  Motor loads require a significant (6 to 10 times full load amps) kick simply to start to run.  This motor starting surge, also called “locked rotor” current, is momentary, only lasts a few milliseconds at peak, and decays to normal running current in roughly a second.  Unfortunately, a static frequency converter doesn’t “know” that this large surge will only last milliseconds, so it shuts down to self-protect.  To run motor loads, the converter’s overload ability must be matched to the motor starting requirement, causing a significant oversizing of the converter.

Static frequency converters are also sensitive to temperature and humid environments.  In essence, they require air conditioning and are not tolerant of severe environments, such as salt fog.  They have a typical lifetime of 10 years of continuous service.

While rotary units are simple, large, and a bit noisy, they are extremely reliable and easy to troubleshoot.  With all else being equal, we’ll ask customers how long they can afford to have the converter down if an unexpected failure occurs.

A rotary unit can be diagnosed by almost anyone with a meter in about an hour and parts can be ordered from a variety of suppliers overnight.  An electronic unit will often require a few hours to troubleshoot and parts can only be ordered through us.  While we attempt to have parts available on-hand, we often have to ship these in from one of our Asian factories which can take up to two weeks.

Additionally, electronic units have an average life of 10-15 years.  A rotary unit, with proper maintenance, can last 50 years or more.

60 Hertz (Hz) is the frequency of wall current in the United States and many other countries across the world. 60 Hertz (Hz) means the rotor of a generator turns 60 cycles per second, and the voltage goes from positive to negative and back to positive - one complete cycle - 60 times every second. Frequency changes are designed to supply safe and stable alternating current (AC) in 50 Hz or 60 Hz frequency from a 50 Hz or 60 Hz input power source.

60 Hz is used by numerous countries spanning the globe including the United States, Canada, Costa Rica, Guam, Rwanda, and Syria. Countries using 50 Hz include Norway and Romania. Saudi Arabia, Japan, and Mexico are among the nations that use both 50 Hz and 60 Hz.

Georator’s high-quality 60 Hz to 50 Hz frequency converters are used to:

  • Test products used in foreign countries using 50 Hz
  • Operate foreign 50 Hz equipment via the USA power grid
  • Military and civilian aircraft simulators
  • Shore-to-ship services
  • Avionics workshops
  • Radar sites
  • Military missions deploying 60 Hz equipment in areas that are primarily 50 Hz countries

Yes, anything with a motor in it will need a frequency converter.  Unfortunately, a converter that will work for just one appliance will cost more than all the appliances in your home.  We recommend buying new appliances in the country you’re going to.

Due to their nature, frequency converters inherently transform the voltage as well.  You are not paying any more to convert voltage.  Adding a transformer only adds to the total cost of the system.

We cannot do this for rotary units because 380V at 60Hz is not a motor we can obtain.  This only leaves us with an electronic converter which cost much more since they must be sized larger to handle motor loads.  It is much more cost effective to skip the transformer altogether.

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