Page 207 - Power Quality in Electrical Systems

Chapter
13

Standby Power Systems

The term standby power systems describes the equipment
interposed between the utility power source and the electrical
load to improve the reliability of the electric power supply to the
load. In previous chapters, we have described the deficiencies
in the electric power supply, such as voltage sags and
interruptions, and their effect on individual types of loads.
The loads that require standby power can range from a single
personal computer supplied by a battery-powered UPS to a
large data processing center. In this chapter, we will describe the
principal components used in standby power systems—namely,
UPSs, transfer switches, and engine-generator (E/G) sets.

Principles: Standby Power System Design
The design of a standby power system for a specific electric-power load
requires consideration of the following factors:
■ Reliability: The questions are
■ What is the power quality of the utility source?
■ What is the cost of a power-quality event?
■ Will the system be required to operate continuously (24/7)?
■ What reliability of the electric power supply is required in terms of
MTBF, minutes per year unavailability, Tiers, or other measures?
■ Maintenance: The questions are
■ Can the load be shut down to perform maintenance or equipment
replacement on the standby power system?
■ Can the standby power system be designed as online, or standby-
redundant, for reliability or maintenance?

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