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A 200 V dc motor has external resistances of Ra and Rf in armature and field circuits respectively. The starting current is reduced when?

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A 200 V dc motor has external resistances of Ra and Rf in armature and field circuits respectively. The starting current is reduced when?

(a) Ra is maximum and Rf minimum

(b) Rf is maximum and Ra minimum

(c) Ra is minimum and Rf minimum

(d) Ra is maximum and Rf maximum

The question was posed to me in homework.

The query is from DC Machine Applications in portion DC Machines of Electrical Machines

1 Answer

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Right choice is (a) Ra is maximum and Rf minimum

Explanation: When Ra is maximum and Rf minimum then the current to the armature is reduced. And hence the sparkings are reduced while starting.

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