Page 51 - Uninterruptible Power Supplies

Source: Uninterruptible Power Supplies and Standby Power Systems

Chapter
2

Interconnecting the Standby and

Normal Supplies

Introduction
This chapter is concerned with a number of matters that have to be con-
sidered before an installation can be designed. It includes such topics
as the distribution of power to the essential and nonessential loads, the
number of generating sets to be installed, their modes of operation and
method of connection, the generated voltage, running in parallel with
the normal supply, overcurrent protection, and the special characteris-
tics of various loads.

Separating the Essential and Nonessential
Loads
Before planning can proceed it is necessary to identify the essential
loads (which receive a supply from the standby generator) and nonessen-
tial loads which are disconnected, and to devise a distribution system
which will achieve the desired operation. Problems can arise and there
are various methods of overcoming them.
If the standby supply is to be included in a new installation the
simplest procedure is for the main switchboard to have two busbar sec-
tions, one supplied from the normal supply and feeding the nonessen-
tial load, the other supplied from the standby supply and feeding the
essential load. The two sections of busbar are connected through a bus
section circuit breaker which is electrically interlocked with the
standby supply circuit breaker and acts as the load shedding device
when the standby supply is in use. When it is necessary to run on
the standby supply the set is started and when it is ready to accept

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