Page 212 - Power Quality in Electrical Systems

194 Chapter Thirteen

Normal Alternate
source source
Static transfer switch

CB CB

Manual
bypass
CB

Utility transf.

Main bus

Non-crit By
load UPS Bat.
pass

UPS bus

Load
Figure 13.6 Two primary-voltage utility feeders with static
transfer switch.

5. UPS plus Two Feeders and a Utility Transfer Switch: An ele-
mentary standby power system utilizing two utility feeders from two
substations is shown in Figure 13.6. In case of a feeder fault or fail-
ure, the utility transfer switch transfers the service to the alternate
feeder. The UPS operates from its battery during the transition.
Other loads, such as air conditioning, heating, and lighting, either
continue to operate or must be restarted.

Engine-Generator Sets
Engine-generator sets (E/G sets) are used in standby power systems to
extend the operation time of the UPS beyond the available discharge
time of the batteries. For large UPSs (for example, larger than 100 kVA),