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For which speed control method we get minimum efficiency?(a) Voltage control method(b) Field control method(c) Armature control method(d) Cannot be determinedI got this question in exam.The origin of the question is Speed Control Using Armature Control in DC Motor in portion DC Motors of DC Machines

Answer»

Correct choice is (c) Armature control method

Easiest explanation: In armature control method, we VARY armature voltage by adjusting variable RESISTANCE value. So, when we define armature efficiency, it is equal to η = [ (Vt-IaRe) Ia] / VTIA= 1-IaRe / Vt. Thus, efficiency is reduced drastically for large SPEED reductions.



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