Page 215 - Power Quality in Electrical Systems

Standby Power Systems 197

■ Control: Electronic isochronous governor for independent operation
and when synchronized to other generators and/or to the utility line.
Active power load division.
■ Generator Protection: Relays to monitor load current, terminal
voltage, reverse power, frequency, over temperature, to operate alarms
and trip the circuit breaker.
■ Voltage Regulator: Electronic regulator for the exciter or main field
current to regulate terminal voltage. Reactive power load division.
■ Synchronizer: Controls engine speed and circuit breaker closing
when the E/G set is to operate in synchronism with the utility line
and/or other E/G sets.
■ Circuit Breaker: Electrically operated. Rated for generator over-
load current and for maximum three-phase short-circuit current.

Operation. The E/G set is a universal, useful, piece of equipment at a
site whose output supplements utility service. Its operation includes the
following functions:

■ Loads: Include UPS, lighting, air conditioning, heating, fans, pumps,
electronic equipment, and appliances. To a degree, loads can draw
non-sinusoidal current (harmonics) and be unbalanced. The generator
must have low subtransient reactance (damper windings) and/or be
oversized for harmonic load current.
■ Emergency Operation: The controls of the transfer switch order the
E/G set to start when an interruption in utility voltage is detected (or
a manual test signal is entered). When the generator voltage has sta-
bilized at the correct amplitude and frequency, the transfer switch
transfers the load to the E/G set. Starting and transfer usually takes
about 10 s. When utility power is restored, the controls allow the E/G
set to run for about 30 min before the transfer switch transfers the
load back to the utility power. Multiple engine-generator sets start in
sequence.
■ Testing: E/G sets for emergency service should be tested about once
a week, and allowed to run at least 30 min. The generator can be
loaded with one of the following: (1) a dummy load, (2) a facility load,
or (3) it can be synchronized to the utility line. The test can be initi-
ated manually or automatically from a programmable controller.
■ Non-emergency Standby: The E/G can be used to provide power to
equipment or facilities when the normal power source is not avail-
able—for example, when they are under construction or maintenance
work is being done. The UPS can be placed on by-pass. Adequate fuel
must be available.