Practice Test GeeksBEE - Bachelor of Electrical Engineering Practice Test
← All BEE Flashcard Decks

Electrical Machines Flashcards

7 cards from real BEE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Electrical Machines flashcards as text

  1. The EMF equation of a DC generator is E = PφNZ / (60A). In a 4-pole lap-wound generator with 600 conductors, flux per pole 0.05 Wb, rotating at 1500 RPM, the generated EMF is:

    Answer: 750 V

    For lap winding A = P = 4; E = 4 × 0.05 × 1500 × 600 / (60 × 4) = 180000 / 240 = 750 V.

  2. Hunting in synchronous machines refers to:

    Answer: Oscillation of the rotor about the synchronous speed position

    Hunting is the oscillation of the rotor angle (and speed) around the equilibrium synchronous position, caused by sudden load changes or disturbances.

  3. To minimize eddy current losses, transformer cores are constructed from:

    Answer: Laminated silicon steel sheets insulated from each other

    Thin laminations insulated from each other break up the eddy current path, drastically reducing eddy current losses which are proportional to the square of lamination thickness.

  4. In a DC series motor, if the load torque is doubled, the speed approximately changes to:

    Answer: 1/√2 of the original speed

    In a series motor T ∝ Ia² and N ∝ 1/Ia; doubling torque requires √2 times the current, so speed drops to N/√2 of its original value.

  5. The primary advantage of an autotransformer over a two-winding transformer of the same rating is:

    Answer: Part of the power is transferred conductively rather than magnetically, reducing copper requirement

    In an autotransformer, power is transferred both conductively (through the common winding) and magnetically, so less copper is needed and efficiency is higher for the same apparent power rating.

  6. A three-phase synchronous generator (alternator) operates at 3000 RPM and produces 50 Hz output. The number of poles it has is:

    Answer: 2

    Using Ns = 120f/P, rearranging P = 120f/Ns = 120 × 50 / 3000 = 2 poles.

  7. The purpose of a damper winding (amortisseur winding) in a synchronous machine is to:

    Answer: Suppress hunting oscillations and assist in starting synchronous motors

    Damper windings are short-circuited rotor bars that produce a torque opposing rotor speed deviations from synchronous speed, thereby damping hunting oscillations and enabling self-starting in synchronous motors.