Practice Test GeeksBEE - Bachelor of Electrical Engineering Practice Test
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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 power factor of a three-phase induction motor operating at no load is:

    Answer: Very low and lagging (0.1–0.2)

    At no load the motor draws mainly reactive magnetizing current with very little active power, resulting in a very low lagging power factor.

  2. In a synchronous generator supplying a lagging power factor load, the effect of armature reaction on the air-gap flux is:

    Answer: Demagnetizing (reduces flux)

    A lagging power factor load causes the armature MMF to oppose the main field MMF, producing a demagnetizing armature reaction.

  3. The rotor construction of a squirrel cage induction motor consists of:

    Answer: Short-circuited aluminum or copper bars embedded in slots

    A squirrel cage rotor has conducting bars (usually aluminum) embedded in rotor slots and short-circuited at both ends by end rings, requiring no external connections.

  4. Voltage regulation of a transformer is correctly expressed as:

    Answer: (VNL - VFL) / VFL × 100%

    Voltage regulation = (VNL − VFL) / VFL × 100%, measuring the change in secondary voltage from full-load to no-load relative to rated (full-load) voltage.

  5. Speed control of a DC shunt motor can be achieved by:

    Answer: Both armature resistance variation and field current variation

    DC shunt motor speed N ∝ V/(φ), so speed can be controlled below base speed by adding armature resistance and above base speed by weakening the field (reducing field current).

  6. In a three-phase induction motor running at slip s, the frequency of the rotor currents is:

    Answer: s × f

    The rotor cuts flux lines at slip speed (s × Ns), so the frequency of rotor currents is s × f, where f is the supply frequency.

  7. An over-excited synchronous motor (field current greater than normal) operates at:

    Answer: Leading power factor

    An over-excited synchronous motor generates more reactive power than it absorbs, acting like a capacitor and drawing leading current from the supply.