Question

Hopkinson’s test is suitable for ______________

(a) Small machines only

(b) Small and medium machines

(c) All machines

(d) Only large machines

I got this question in my homework.

I'd like to ask this question from Hopkinson’s Test in portion Efficiency and Testing of DC Machines

Answer 1

Correct answer is (d) Only large machines

The explanation is: A large variation of field currents is required for small machines, the full-load set speed is usually higher than the rated speed and the speed varies with load. The full load in small machines cannot obtained by cutting out all the external resistances present in the generator field. Sufficient reduction in the motor field current is necessary to achieve full-load conditions resulting in speeds greater than the rated value.