Introduction

This chapter is concerned with a number of matters that have to be considered 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 characteristics 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 nonessential 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 sections, one supplied from the normal supply and feeding the nonessential 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 load, the bus section breaker is tripped and, after a short delay, the standby supply breaker is...