Page 217 - Power Quality in Electrical Systems

Standby Power Systems 199

Figure 13.9 Automatic transfer
switch with optional bypass- iso-
lation switch [13.5].

■ Solid State: Utilizes thyristor or GTO AC switches in each leg, as
shown in Figure 13-6. Transfer switches have been built for switch-
ing utility feeders rated up to 34 kV.

Applications. Applications for transfer switches include nearly every
area of electrical application, particularly those devoted to high relia-
bility and safety. These include the following:

■ Utility to E/G Set: A generic diagram is shown in Figure 13.10. The
shape of the movable contact is typical to obtain a short travel distance
and no ambiguity of contact positions.
■ UPS Supply: Transfer from a utility line to an E/G set to supplement
the UPS battery. Data centers employ up to 10,000 kVA of E/G sets
and suitable transfer switches.
■ Electric-Motor Transfers: For large induction motor–driven fans
and pumps, as in power plants, transfer switches are employed where
two alternate transformers or feeders are provided.
■ Lighting: Alternate and emergency lighting systems supplied by
transfer switches from batteries, inverters, and alternate feeders.