Explain the Hopkinson’s test for determination of efficiency of shunt machines.
Answers
Hopkinson's Test is another useful method of testing the efficiency of a DC machine. It is a full load test and it requires two identical machines which are coupled to each other. One of these two machines is operated as a generator to supply the mechanical power to the motor and the other is operated as a motor to drive the generator. For this process of back to back driving the motor and the generator, Hopkinson's test is also called back-to-back test or regenerative test.
If there are no losses in the machine, then no external power supply would have needed. But due to the drop in the generator output voltage we need an extra voltage source to supply the proper input voltage to the motor. Hence, the power drawn from the external supply is therefore used to overcome the internal losses of the motor-generator set. Hopkinson’s test is also called regenerative test or back to back test or heat run test.
Hopkinson's Test is another useful method of testing the efficiency of a DC machine. It is a full load test and it requires two identical machines which are coupled to each other.
Calculation of Efficiency by Hopkinson's Test
Let, V = supply voltage of the machines.
Then,
I 1 = The current from the generator
I 2 = The current from the external source
And, Generator output = VI 1..................(1)
Let, both machines are operating at the same efficienc