More information on Motor Generator Sets

Kato Engineering motor-generator (MG) sets offer many advantages over solid-state systems:

• Long life: 100,000 hours on the MG set before major overhauls. Components are standard and available. Many MG sets built by Kato have been running successfully for decades.
• Low maintenance cost: The equipment can be maintained by electricians and/or mechanics; no specialist is required. Also, on horizontal, single-shaft MG sets, there is no coupling, gear nor belt to wear out. Exciters are brushless; there are no commutators or brushes to replace.
• Low harmonic content on the input and output of the MG set from no load to full linear load.
• Low impedance for harmonics.
• High overload capability and a sustaining short circuit capability of 300% of nominal amps for 10 seconds.
• 1.0 power factor at the input without power factor correction.
• Simple, rugged construction for tolerance to voltage sags, spikes and noise, as well as complete isolation input to output.
• Gradual failure mechanisms (MG sets usually do not fail abruptly).
• Tolerance to heat, dust moisture and other environmental conditions.
• Built with the latest technology and backed by over 90 years of experience in building rotary MG sets

Solid state systems:

• Have a life that would typically be shorter than the rotary MG set: The electronic components that are essential to the static converter become obsolete faster than those on a rotary MG set.
• Will likely require an electrical expert for service: This expert will probably only be available from the manufacturer.
• Have harmonics on the input and output: harmonic filters may have to be added on the input and output, and this is normally quite costly.
• Are sensitive to voltage sags, spikes and noise and do not provide isolation input to output, which is obtained with an MG set.
• Have electronic components that are sensitive to heat, dust and moisture.
• Are not proven technology and are often supplied by relatively small companies with limited experience. 

No-Load Testing
For no-load loss and heat run testing, these sets provide clean power with accurate regulation and voltage control. Several configurations are available:

• 1500 or 1800 RPM 50-50 Hz or 60-60 Hz: When no frequency conversion or adjustments are required. Often part of a multiple-output set in conjunction with a 150-Hz or 180-Hz generator.
• 600 RPM 50-60 Hz or 60-50 Hz: When testing transformers at a rated frequency that is different from the local frequency.
• Variable frequency: By using a variable-frequency drive and motor to power these sets, any output frequency in the 50 Hz to 60 Hz range may be selected. This set is most useful when either frequency may be used for testing.
• MGG: For larger range requirements, like 50-to-180 or 50-to-200 Hz, it is most economical to use two generators, one 50-to-60 Hz and the other 100-to-200 Hz. These generators may be able to be driven by the same motor.
  

90 to 400 Hz Induced Voltage Testing
These sets are used to energize the transformer at voltages exceeding its normal rating, in order to test its capability to withstand high voltages. They usually require low distortion and low partial discharge to permit detection of leakage in the tested transformer.

Special Application and Multiple Sets
For a more compact or economical installation, it is common to combine a nominal frequency generator and a high-frequency one with a common motor on the same base. Kato Engineering also supplies specialty M-G sets for testing of other equipment at frequencies from 25-1200 Hz, single or multiple phases (depending upon ratings).

• The generator can be designed to operate with either leading or lagging power factor while remaining stable even at full output.
• Frequency range/variable frequency: Normal frequencies are 50 and 60 Hz for no load tests, and either 150 or 180 Hz for induced-voltage tests.  Smaller sets are available at 200 or 240 Hz, 300 or 360 Hz, and 400 Hz.
• By using a variable-frequency drive on the input, it is possible to build a set with wide frequency range such as 100-200 Hz, which may be advantageous for tuning the test system to a resonant frequency. A more than 2:1 frequency range is usually not economical, however.