For large motors what is the ratio of compensating winding is required for increasing the speed of the motor?(a) 2:1(b) 4:1(c) 6:1(d) 8:1This question was posed to me in a national level competition.My enquiry is from Speed Control Using Field Control of Series Motor topic in section DC Motors of DC Machines

For large motors what is the ratio of compensating winding is required

1.	For large motors what is the ratio of compensating winding is required for increasing the speed of the motor?(a) 2:1(b) 4:1(c) 6:1(d) 8:1This question was posed to me in a national level competition.My enquiry is from Speed Control Using Field Control of Series Motor topic in section DC Motors of DC Machines
Answer» RIGHT CHOICE is (a) 2:1 Easiest explanation: For motors requiring a wide range of speed control, the field ampere-turns are much smaller than the armature ampere-turns at HIGH speeds causing extreme distortion of the flux density in the air-gap. This LEADS to poor COMMUTATION. Compensating winding can be used to increase the speed range which can be 2 to 1 for large motors.

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