STANDBY GENERATOR SYSTEM FOR ELECTRONIC EQUIPMENT BASIC INFORMATION AND TUTORIALS

Incompatibility issues regarding emergency standby generator systems and downstream electronic load equipment are gaining more recognition in modern power systems. UPS systems and electronic load equipment can be very susceptible to voltage waveform distortion and frequency variations.

The distortion of the voltage waveform is primarily a function of the magnitude and harmonic content of the load current and the impedance of the upstream electrical distribution system. Standby generator systems generally have a much higher impedance than the utility system.

Therefore, the voltage waveform distortion typically increases when loads are fed by standby generator power. One of the most common incompatibility situation is with generator systems and downstream UPS systems.

These situations can range from problems with the UPS inverter trying to synchronize to the static bypass circuit to the UPS input failing to accept the input voltage and thus causing the UPS system to go to battery power.

In this latter condition, the voltage distortion typically improves when the load is fed from battery power (the load is now on battery and not acting on the impedance of the generator system) and the UPS input accepts the line voltage. Once again, voltage distortion can increase when the loads are powered via the UPS system, and the UPS

a) Isochronous electronic governor to regulate frequency. These governors typically maintain frequency regulation within 0.25% of the setting, as opposed to approximately 3% for mechanical governors.

b) Permanent magnet excitation system or filtering means to isolate the voltage regulator
power circuit from the distorted waveform.

c) Generators with a 2/3 pitch stator winding design to minimize third harmonic waveform distortion.

d) Low subtransient reactance to minimize voltage waveform distortion. cycles back and forth on battery power. Recommended practice is to provide the standby generator manufacturer with information on the type, rating, and characteristics of the electronic load equipment.

Many generator manufacturers and UPS manufacturers have guidelines for sizing emergency generators when supplying UPS systems. This rating will typically depend on the type and size of the UPS system.

In general, the standby generators should have the following characteristics to minimize adverse interactions when supplying nonlinear loads.