All Free Electrical Engineering MCQs with Answers

• A. Swinburne's test
• B. Hopkinson's test
• C. Field test
• D. Brake test

Explanation: Field’s test is suitable for two similar large D.C. series motors because the machines can be mechanically coupled and tested under load…

• A. iron losses
• B. line losses
• C. sparking
• D. corona losses

Explanation: Locating generators near load centres shortens the transmission and distribution lines, thereby reducing I²R losses in the line…

• A. yoke
• B. commutator
• C. armature conductors
• D. armature rotor

Explanation: Iron losses consist of hysteresis and eddy-current losses, and they occur mainly in the laminated armature core as it rotates through the…

• A. full-load
• B. rated r.p.m.
• C. rated voltage
• D. all of the above

Explanation: A DC generator is normally designed so that its highest efficiency occurs close to full-load operation, where its fixed losses and…

• A. eddy current losses = stray losses
• B. hysteresis losses = eddy current losses
• C. copper losses = 0
• D. variable losses = constant losses

Explanation: Maximum efficiency occurs when the variable losses, chiefly armature copper loss, equal the constant losses, such as iron, friction and…

• A. 100 W
• B. 500 W
• C. 1000 W
• D. 1500 W

Explanation: A well-designed 10 kW generator commonly has total losses of roughly 5% of its rating, giving about 0.05 × 10,000 = 500 W.

• A. Hysteresis losses
• B. Eddy current losses
• C. Copper losses
• D. Windage losses

Explanation: Laminating the magnetic core increases the resistance of paths available for circulating currents, sharply reducing eddy-current loss.

• A. Mechanical loss
• B. Core loss
• C. Copper loss
• D. All of the above

Explanation: Mechanical losses, core losses and copper losses all ultimately appear as heat: friction and windage heat moving parts, core losses heat…

• A. Providing laminations in armature core
• B. Providing laminations in stator
• C. Using non-magnetic material for frame
• D. Using material of low hysteresis co-efficient for armature core material

Explanation: Hysteresis loss depends on the magnetic material and is reduced by using armature-core material with a low hysteresis coefficient.

• A. over load relay is connected in series and no volt relay in parallel with the load
• B. over load relay is connected in parallel and no volt relay in series with the load
• C. over load relay and no volt relay are both connected in series with the load
• D. over load relay and no volt relay are both connected in parallel with the load

Explanation: The overload relay is placed in series with the motor circuit so excessive current trips it, while the no-volt release coil is connected…

• A. trains
• B. cranes
• C. hoists
• D. machine tools

Explanation: DC shunt motors provide nearly constant speed with good speed regulation, making them suitable for machine tools.

• A. magnetic field
• B. active length of the conductor
• C. current flow through the conductors
• D. number of conductors
• E. radius of armature
• F. all above factors

Explanation: Motor torque follows the force on the armature conductors, with T proportional to flux, current, conductor length, number of conductors…

• A. Field copper loss
• B. Windage loss
• C. Armature copper loss
• D. None of the above

Explanation: Armature copper loss is Iₐ²Rₐ, so it changes substantially as load current changes.

• A. hysteresis loss
• B. field copper loss
• C. armature copper loss
• D. eddy current loss

Explanation: At rated load, armature current is high and the armature copper loss, Iₐ²Rₐ, rises accordingly.

• A. Loss of efficiency
• B. Excessive heating of core
• C. Increase in terminal voltage
• D. Rise in temperature of ventilating air

Explanation: Iron losses convert electrical energy into heat, reducing efficiency and increasing the core and ventilating-air temperature.

• A. Frequency of magnetic reversals
• B. Maximum value of flux density
• C. Volume and grade of iron
• D. Rate of flow of ventilating air

Explanation: Hysteresis loss depends mainly on frequency of reversal, maximum flux density, and the volume and magnetic quality of the iron.

• A. high initial cost
• B. high maintenance cost
• C. low efficiency at Hght loads
• D. all of the above

Explanation: Ward-Leonard control requires a motor-generator set, giving high initial and maintenance costs and poor efficiency at light loads because…

• A. residual magnetism of the generator
• B. core losses of motor
• C. mechanical losses of motor and generator together
• D. all of the above

Explanation: At very low speed, the motor needs only a small applied voltage, but the Ward-Leonard generator cannot reduce its output below the voltage…

• A. Field control
• B. Armature voltage control
• C. Shunt armature control
• D. Mechanical loading system

Explanation: Armature-voltage control changes speed while keeping the field flux nearly constant, so motor torque can remain constant over the control…

• A. voltage control method
• B. field divertor method
• C. field control method
• D. armature resistance control method

Explanation: In Ward-Leonard control, a motor-generator set varies the voltage supplied to the controlled motor armature.