10-06-2017, 07:07 AM
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AIM
To conduct OC, SC and ZPF test on the three phase alternator and to predetermine the regulation of 3 phase alternator by EMF method, MMF method, & ZPF method also to verify by vector diagram.
APPARATUS REQUIRED
PRECAUTION
1. The motor field rheostat should be kept in the minimum resistance position.
2. The alternator field potential divider should be in the minimum voltage position.
3. Initially all switches are in open position.
PROCEDURE
A. OC.Test
1. Note down the name plate details of motor and alternator
2. Connections are given as per circuit diagram.
3. The DPST is closed on supply side.
4. Using three point starter, the motor is started. The alternator is brought to Rated speed by varying motor field rheostat.
5. By varying the alternator field potential divider in steps, for various values of field current, the voltmeter readings across the alternator are noted by keeping the TPST switch under normal condition.
6. The OCC curve (Eph Vs If ) is drawn from the above rating.
B. SC Test
1. By ensuring the zero voltage across the alternator TPST switch is closed to position 1.
2. SC test is conducted with alternator armature rated current which has been set by adjusting alternator field potential divider and corresponding field current is noted.
3. The SC curve (Isc Vs If ) is drawn from the above rating.
C. ZPF Test
1. Connections are made as per the circuit diagram.
2. Give the supply by closing the DPST switch.
3. Using the Three Point Starter start the motor to run at the synchronous speed by varying the motor field rheostat.
4. By varying the alternator field potential divider in steps, for various values of field current, the Voltmeter readings across the alternator are noted by keeping the TPST switch under normal condition.
5. Conduct a Short Circuit Test by closing the TPST switch to position 1 and adjust the potential divider to circulate the rated Armature Current and tabulate the corresponding field current.
6. To conduct a ZPF test change the TPST switch to position 2.
7. Adjust the alternator field potential divider for Full Load current passing through either Inductive load with zero power factor and tabulate the readings.