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This set of Electrical Machines Multiple Choice Questions & Answers

(MCQs) focuses on “Generated EMF”.

1. Which of the following statements is/are correct regarding the generation

of EMF in rotating electrical machines in the armature winding? EMF is

generated

a) by rotating armature windings through a magnetic field

b) by rotating magnetic field with respect to the armature windings

c) by designing the magnetic circuit to have variable reluctance with rotor

rotation

d) any of the mentioned

View Answer

Answer:d

Explanation: Any of the above mentioned methods will produce EMF in the armature windings.

2. The EMF equation e = NωrΦsinωrt is applicable to a) AC systems with time variant field flux b) DC systems with time variant field flux c) both AC and DC systems with time invariant field flux d) both AC and DC systems with time variant field flux View Answer Answer:c Explanation: e = NωrΦsinωrt-NdΦ/dtcosωrt, for time invariant field flux dΦ/dt = 0 ⇒ e = NωrΦsinωrt, is the general equation, and is applicable to both AC and DC systems. 3. In the equation for RMS value of the generated EMF in a full pitched coil of an AC machine, E = Emax/√2 = √2πfrNΦ, fr depends on a) rotating speed of the armature coil b) rotating speed of the flux density wave c) relative velocity between the flux density wave and armature coil d) any of the mentioned View Answer