MCQ Subject: Electrical Machines & Transformers

In a DC motor, armature reaction primarily causes which of the following effects during operation?

A double-winding transformer has a primary coil with 500 turns and a secondary coil with 200 turns. If the primary voltage is 440V and the secondary voltage is 176V, what is the turns ratio (primary:secondary) and the approximate efficiency if primary power is 11kW and secondary power is 10.5kW?

Which cooling method is commonly used for large power transformers?

A three-phase transformer bank consists of three identical single-phase transformers connected in a Y-Δ configuration. If the primary voltage is 11 kV (line-line) and the secondary voltage is 400 V (line-line), what is the turns ratio of the transformers?

A transformer exhibits negative voltage regulation under which load condition?

A single-phase transformer rated at 10 kVA, 440 V/220 V has a full-load copper loss of 200 W. The full-load magnetizing power (in VA) at the primary side, assuming the efficiency is highest at this load, is:

At what power angle does a synchronous motor start to become unstable?

In a transformer operating on the principle of electromagnetic induction, which statement is accurate regarding the primary and secondary windings?

What is the primary purpose of a tap changer in a transformer?

In a synchronous motor, which of the following operating conditions corresponds to the motor behaving as an inductive load?