Page 213 - Power Quality in Electrical Systems

Standby Power Systems 195

the battery time is usually only several minutes. The transfer from util-
ity line to E/G set, including starting and stabilizing the generator for
frequency and voltage, can be accomplished in about 10 s. Sometimes a
short time delay is introduced in starting to avoid too frequent E/G
starts for short-time voltage sags and interruptions that can be handled
by the batteries of the UPS.
Engine-generator sets are available from 50 to 2500 kVA. A 218-kVA
diesel-engine generator set is shown in Figure 13.7 [13.1]. For larger
loads, it is common to employ multiple E/G sets operating in parallel to
obtain reliability through redundancy and to have a set available for
maintenance. In addition, electric power is required for non-UPS load—
that is, air conditioning, lighting, and water pumps. Combustion tur-
bines are also employed to drive generators in standby applications.

Standards
The major problem for the installation of E/G sets is environmental. The
sets produce noise, exhaust, and vibration; they require coolant air or
water, fuel, and fuel systems; they are heavy and require adequate foun-
dations. A list of codes and standards governing E/G sets as an alter-
native to utility power includes the following:
■ ANSI/IEEE 446-1995, “Recommended Practice for Emergency
and Standby Power Systems for Industrial and Commercial
Applications” [13.2]

Figure 13.7 Diesel engine-generator set. Rating: 175 kW, 0.8 PF,
480 Y / 277 V, 60Hz [13.1].