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Experiment_10_The_alternator_under_load - Experiment 10 The...

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10 1 Experiment 10 The Alternator Under Load OBJECTIVE To determine the voltage regulation characteristics of the alternator with resistive, capacitive and inductive loading. To observe the effect of unbalanced loads on the output voltage. DISCUSSION The output voltage of an alternator depends essentially upon the total flux in the air-gap. At no- load, this flux is established and determined exclusively by the DC field excitation. Under load, however, the air-gap flux is determined by the ampere-turns of the rotor and the ampere-turns of the stator. The later may aid or oppose the MMF (magnetomotive force) of the rotor depending upon the power factor of the load. Leading power factors assist the rotor, and lagging power factors oppose it. Because the stator MMF has such an important effect upon the magnetic flux, the voltage regulation of alternators is quite poor, and the DC field current must continuously be adjusted to keep the voltage constant under variable load conditions. If one phase of a three-phase alternator is heavily loaded, its voltage will decrease due to the IR and IX L drops in the stator winding. This voltage drop cannot be compensated by modifying the DC field current because the voltages of the other two phases will also be changed. Therefore, it is essential that three-phase alternators do not have loads that are badly unbalanced. EQUIPMENT REQUIRED Workstation Power supply, Three-Phase Synchronous Motor/Generator, DC Motor/Generator, Resistive Module, AC Ammeter, AC Voltmeter, and DC Voltmeter/Ammeter
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10 2 Other devices Tachometer PROCEDURE CAUTION!
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Experiment_10_The_alternator_under_load - Experiment 10 The...

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