Question

For the given traction application using a dc series motor for a starting time ’t’ is applied. If this method is replaced by a series-parallel control, giving 50% time for each series and parallel. The saving in the starting energy of _________

(a) 25%

(b) zero

(c) 50%

(d) 75%

I got this question in quiz.

The query is from Losses and Efficiency in portion Rating and Loss Dissipation of Electrical Machines

Answer 1

Right option is (a) 25%

The explanation is: Initially let the energy utilized was 100% for time t.Then for 50% duration for series, energy used is 50%. For parallel operation for the same circuit, the resistance gets halved assuming the same machine. So, for 50% of the parallel operation, 25% of energy is only utilized. Hence total saving is 25%.