Page 245 - Uninterruptible Power Supplies

Source: Uninterruptible Power Supplies and Standby Power Systems

Chapter
10

Some System Failures: The Light

of Experience!

Introduction
It is part of an engineer’s education to experience an occasional failure.
The incidents which are briefly described in the following paragraphs
have been included in this book in the hope that readers will benefit
from them. They demonstrate the need for lateral thinking at the plan-
ning or design stage and the truth of the dictum that if it can happen it
probably will.

Lack of Ventilation
This failure occurred at a prestigious multiset installation having a
rated output of several megawatts several years after it had been com-
missioned. Test runs had been conducted at regular intervals and the
operating personnel were confident that it would perform satisfactorily
when it was required to do so.
A prolonged supply failure was, however, to prove their confidence
misplaced; the sets started and supplied the load but after about 20 min
there was a complete shutdown due to overtemperature. The reason
was surprisingly simple, the duct carrying the engine-room ventilation
air had been blanked off and there was no air flow. It is believed that
contractors working in the winter had blanked off the duct for the ben-
efit of their workers and had departed without removing it.
This failure demonstrates the need for test runs to be on load and of
sufficient duration for thermal stability to be reached; until this fail-
ure, test runs had been of short duration.

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