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AIM:
To predetermine the regulation of three phase alternator by Potier and ASA methods and also to draw the vector diagrams.
FORMULAE USED:
Percentage regulation = Eo – Vrated x 100 (For both POTIER & ASA methods)
Vrated
PRECAUTION:
(i) The motor field rheostat should be kept in the minimum resistance position.
(ii) The Alternator field potential divider should be in the position of minimum potential.
(iii) Initially all switches are in open position.
PROCEDURE FOR BOTH POTIER AND ASA METHODS:
1. Note down the complete nameplate details of motor and alternator.
2. Connections are made as per the circuit diagram.
3. Switch on the supply by closing the DPST main switch.
4. Using the Three point starter, start the motor to run at the synchronous speed by varying the motor field rheostat.
5. Conduct an Open Circuit Test by varying the Potential Divider for various values of Field current and tabulate the corresponding Open circuit voltage readings.
6. Conduct a Short Circuit Test by closing the TPST knife switch and adjust the potential divider the set the rated Armature current, tabulate the corresponding Field current.
7. Conduct a ZPF test by adjusting the potential divider for full load current passing through either an inductive or capacitive load with zero power and tabulate the readings.
8. Conduct a Stator Resistance Test by giving connection as per the circuit diagram and tabulate the voltage and Current readings for various resistive loads.
PROCEDURE TO DRAW THE POTIER TRIANGLE (ZPF METHOD):
(All the quantities are in per phase value)
1. Draw the Open Circuit Characteristics (Generated Voltage per phase VS Field Current)
2. Mark the point A at X-axis, which is obtained from short circuit test with full load armature current.
3. From the ZPF test, mark the point B for the field current to the corresponding rated armature current and the rated voltage.
4. Draw the ZPF curve which passing through the point A and B in such a way parallel to the open circuit characteristics curve.
5. Draw the tangent for the OCC curve from the origin (i.e.) air gap line.
6. Draw the line BC from B towards Y-axis, which is parallel and equal to OA.
7. Draw the parallel line for the tangent from C to the OCC curve.
8. Join the points B and D also drop the perpendicular line DE to BC, where the line DE represents armature leakage reactance drop (IX¬L)
BE represents armature reaction excitation (Ifa).