Page 74 - Uninterruptible Power Supplies

Interconnecting the Standby and Normal Supplies
72 Chapter Two

Resistor

Resistor

R Y B E
Figure 2.16 Neutral earthing of high-voltage multiple sets each gen-
erator having its own resistor.

Paralleling the Standby and Normal Supplies
Introduction
A facility that allows the standby supply to be occasionally run in paral-
lel with the normal supply is extremely useful. Although paralleling is
applicable to installations of any rating, in practice the facility is used
with larger installations having ratings of say 500 kVA and above. It will
require the agreement of the network operator and there will be require-
ments regarding the earthing arrangements, the protection relays fitted
to the interconnecting circuit breaker and the operating procedures. The
network operator must be satisfied that the operating personnel will be
competent and will be available as and when necessary.
The advantage to be gained from the paralleling facility is the ability
to transfer the load from one supply to the other without the load expe-
riencing a break in supply. After running on the standby supply it is
possible to return the essential load to the normal supply without a

Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2004 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.