EFFECT OF TEMPERATURE ON VOLTAGE REGULATION
TESTING AND ADJUSTING
SUBJECT:
Effect of Temperature on Voltage Regulation
BUSINESS:
Building Services, Marine/Petroleum, Material Handling
PRODUCT/APPLICATION:
Generator Sets, SRCR or SR 4 Generators
The operating voltage of a cold (just started) generator
will be slightly higher than the operating voltage when
the generator has been under load and warm. Assume
an SRCR or SR 4 Generator is started when the
temperature has stabilized at 25ºC. The full load voltage
of the SRCR Generator would decrease a maximum of
3% when the generator temperature stabilized at 100ºC.
The full load voltage of an SR 4 Generator would
decrease a maximum of 1% when this generator
stabilized at 100°C. Most of the voltage decrease
occurs in about 30 minutes. Generally, temperatures of
generators stabilize within two hours.
The effect of cold-to-hot resistance change on generated
voltage is rarely observed in a single SRCR or SR 4
Generator. A correctly adjusted voltage regulator
compensates for most of the voltage differences due to
resistance changes and due to speed changes which
result from increases or decreases in load. The
recommended adjustment procedure is printed in
operators' books and on the inside of a generator side
panel.
The effect of the small voltage change, cold-to-hot, is
observable when paralleling a correctly adjusted cold
generator with a correctly adjusted generator that has
been carrying load for an hour or more. The resulting
voltage difference, although small, causes a circulating
current between generators. There is no cause for
concern as the circulating current will diminish as the
oncoming unit increases in temperature.
The recommended adjustment for parallel operation
makes each generator set voltage the same at operating
temperature. This assures the most stable operation
with lowest circulating currents in unsupervised systems.
However, if a supervised system includes power factor
meters, an operator can at any time adjust the individual
generator set voltage level controls as needed to
minimize circulating currents.
You may want to retain the January 1973 issue of this
Engine Data Sheet for reference on early equipment.
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