EFFECT OF TEMPERATURE ON VOLTAGE REGULATIONTESTING AND ADJUSTINGSUBJECT:Effect of Temperature on Voltage RegulationBUSINESS:Building Services, Marine/Petroleum, Material HandlingPRODUCT/APPLICATION:Generator Sets, SRCR or SR 4 GeneratorsThe operating voltage of a cold (just started) generatorwill be slightly higher than the operating voltage whenthe generator has been under load and warm. Assumean SRCR or SR 4 Generator is started when thetemperature has stabilized at 25ºC. The full load voltageof the SRCR Generator would decrease a maximum of3% when the generator temperature stabilized at 100ºC.The full load voltage of an SR 4 Generator woulddecrease a maximum of 1% when this generatorstabilized at 100°C. Most of the voltage decreaseoccurs in about 30 minutes. Generally, temperatures ofgenerators stabilize within two hours.The effect of cold-to-hot resistance change on generatedvoltage is rarely observed in a single SRCR or SR 4Generator. A correctly adjusted voltage regulatorcompensates for most of the voltage differences due toresistance changes and due to speed changes whichresult from increases or decreases in load. Therecommended adjustment procedure is printed inoperators' books and on the inside of a generator sidepanel.The effect of the small voltage change, cold-to-hot, isobservable when paralleling a correctly adjusted coldgenerator with a correctly adjusted generator that hasbeen carrying load for an hour or more. The resultingvoltage difference, although small, causes a circulatingcurrent between generators. There is no cause forconcern as the circulating current will diminish as theoncoming unit increases in temperature.The recommended adjustment for parallel operationmakes each generator set voltage the same at operatingtemperature. This assures the most stable operationwith lowest circulating currents in unsupervised systems.However, if a supervised system includes power factormeters, an operator can at any time adjust the individualgenerator set voltage level controls as needed tominimize circulating currents.YoumaywanttoretaintheJanuary1973issueofthisEngineDataSheetforreferenceonearlyequipment.99
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