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Electrical Lab Experiments

To perform Swinburne's test on the given DC machine



AIM: To perform Swinburne’s test on the given D.C machine and predetermine the efficiency at any desired load both as motor and as generator.

Name Plate Details:

Apparatus Required:

Circuit Diagram:

Circuit Diagram To Find Armature Resistance:

Theory:

This test is to find out the efficiency of the machine .It is a simple indirect method in which losses are determined separately and from their knowledge, efficiency at any desired load can be predetermined. The only test needed is no-load test. This test cannot be performed on DC series motor. The machine is run as a no load shunt motor at rated speed and with a rated terminal voltage .However, this test is applicable to those machines in which flux is practically constant.

Procedure:

1) Make all the connections are as per the circuit diagram.

2) Keep the field rheostat in minimum resistance position.

3) Excite the motor with 220V, DC supply by closing the DPST switch and start the Motor by moving the handle of 3-point starter from OFF to ON position.

4) By adjusting the rheostat in motor field bring the speed of the motor to its rated value. Note down the readings of Ammeter and Voltmeter at no load condition.

5) The necessary calculations to find efficiency of machine as motor & generator at any given value of armature current is done.

To Find Armature Resistance (Ra):

1) Connect the circuit per the circuit diagram.

2) Keep the rheostat in maximum position.

3) Now excite the motor terminals by 30V supply by closing DPST switch.

4) Note down the readings of Ammeter and voltmeter.

Model Calculations:

For generator:

For motor:

Tabular Coloumn:

Armature Resistance (Ra):

Calculation Table:

As a Motor:

As a Generator:

Model Graph:

Precautions:

  • We should start the motor under no load.
  • Take the reading without parallax error.
  • The connections must be tight.

Result:

Viva Questions:

  1. Why the magnetic losses calculated by this method are less than the actual value?
  2. Is it applied to D.C series machines?
  3. Comment on the efficiency determined by this method.








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