Generators - Specifications & Selection

Motor-generators (or MG sets) are available with single- or three-phase motors and a variety of sizes. There are three basic types of MG sets. Each type uses a generator to supply power to the equipment. The difference in the units is their method of supplying power to the generator.

Induction Motors are the least expensive type of MG set. The frequency regulation of these units is the least precise.

DC Motors have the advantage of supplying an output frequency that is different than the input frequency. Some computer systems operate on higher frequency power than that supplied by the utility. This type of MG set is often used for these computers.

Finally, synchronous motors are the most expensive type of MG set. The frequency regulation for these units is the most precise.

There are several important considerations in selecting an MG set. These are:

  • Total electrical isolation,
  • Output voltage regulation of + or -1% for an input of +15% to -30%,
  • UL listing,
  • An overload capability of 150% for 1 minute, 130% for 30 minutes, and 115% for 120 minutes,
  • A Total Harmonic Distortion of less than 3%,
  • Step voltage response of + or -1.5% for 10% Step load, + or -5% for 30% step load, and + or -7% for 50% step load, and
  • A manufacturer's warranty of at least one year.