Page 233 - Uninterruptible Power Supplies

Source: Uninterruptible Power Supplies and Standby Power Systems

Chapter
9

Notes on Systems Installation

This chapter provides guidance on creating a complete system. Although
not exhaustive it will give guidance and illustrate areas where problems
may be envisaged.
The quintessential question is system power rating. It is surprising
how hindsight illustrates how easily errors occur in this area. For exam-
ple, the usage of computer systems inevitably grows with time, and
often it is difficult for the exact rating to be determined. Here are a few
points which need examination: The existing computer has every
chance of expansion, but by how much and over what time period. Is it
feasible that the computer may be reduced in size and much of its work
is delegated to peripheral computer centers?
The possibility of adding further power blocks at a later stage, and
thus paralleling UPS units and prime movers will have to be consid-
ered, it should be noted that if this decision is preferred the eventual
system cost will be increased.
Although we have considered computers, the same considerations
should also apply to other loads. Lighting has its own particular aspects
requiring attention. Discharge lamps do have fairly high starting cur-
rents, and some discharge lamp circuits will necessitate consideration
of waveform effect on the UPS and, indeed, the generator. It should also
be remembered that even the mundane Tungsten lamp has a starting
surge of approximately 12 to 15 times normal run current, and halogen
lamps approximately 20 times normal run current. These starting surges
are transient, lasting no longer than approximately 5 to 10 Hz, but it is
advisable to take such surges into consideration.
Motor loads will usually give starting surges and here we are looking
at surges up to 15 times normal full-load current and certainly the
decay time to normal operation will be rated in seconds.

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