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GATE 2021 EE – Question 18

Electrical Machines · Synchronous machines: cylindrical and salient pole machines, performance and characteristics, regulation and parallel operation of generators, starting of synchronous motors · 1 mark · Multiple choice

Consider the table given:

Constructional featureMachine typeMitigation
(P) Damper bars(S) Induction motor(X) Hunting
(Q) Skewed rotor slots(T) Transformer(Y) Magnetic locking
(R) Compensating winding(U) Synchronous machine(Z) Armature reaction
(V) DC machine

The correct combination that relates the constructional feature, machine type and mitigation is

  1. P-V-X, Q-U-Z, R-T-Y
  2. P-U-X, Q-S-Y, R-V-Z
  3. P-T-Y, Q-V-Z, R-S-X
  4. P-U-X, Q-V-Y, R-T-Z

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Show answer and explanation

Correct answer: (B) P-U-X, Q-S-Y, R-V-Z

Explanation

Damper bars are fitted to synchronous machines to suppress hunting (P-U-X). Skewed rotor slots in induction motors prevent magnetic locking (cogging) between stator and rotor teeth (Q-S-Y). Compensating windings in DC machines counter armature reaction (R-V-Z).