Page 91 - Uninterruptible Power Supplies

Source: Uninterruptible Power Supplies and Standby Power Systems

Chapter
3

Additional Information Relating to

the Standby Supply Installation

Introduction
This chapter is concerned with various matters which do not fit com-
fortably into either of the two previous chapters. The calculation of
engine and generating ratings is a somewhat tortuous exercise and has
been left until this late stage in the book so that the reader has the ben-
efit of text appearing in earlier parts of the book. The components of the
load current, characteristics of particular loads, vibration, and noise
are discussed.
In this chapter the expressions kWm and kWe are used to denote
mechanical and electrical power respectively.

Sizing the Engine and Generator
The Power Rating of the Engine
The factors to be considered in sizing the engine are:

■ The class of power rating specified for the generating set (continuous
power, prime power, or limited time running power)
■ The frequency performance class G1, G2, G3, G4, or as otherwise
specified (see Table 1.1)
■ The maximum load (kWm) to be supplied
■ The maximum step of load (kWm) to be applied
The engine must be capable of supplying the total required mechan-
ical load to the generator. This will be higher than the electrical load

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