Electrical Engineering MCQ Question and Answer
Electrical Engineering MCQ Question and Answer
1. The stator of a 415V, 50Hz, 6-pole, 970 rpm, 3- phase slip ring induction motor is fed with normal voltage. The rotor with slip rings open-circuited is rotated at 500 rpm along the normal direction of its rotation. The frequency of the voltage across slip rings will be
- 1.5 Hz
- 25 Hz
- 26.5 Hz
- 75 Hz
2. A five-limbed core is sometimes used to construct a three-phase power transformer to be connected star/star with isolated neutrals to reduce
- Magnetizing current harmonics
- Core losses
- Leakage reactance
- Zero sequence impedance
3. The phenomenon of crawling is usually not formed in slip-ring because these motors have
- no space harmonics
- high resistance rotor windings
- no zig-zag leakage
- Comparatively large air-gap
4. To increase the visual critical voltage of corona for an overhead line, one solid phase-conductor is replaced by a “bundle” of four smaller conductors per phase, having an aggregate cross-sectional area equal to that of the solid conductor. If the radius of the solid conductor is 40 mm, then the radius of each of the bundle conductors would be
- 10mm
- 20 mm
- 28.2 mm
- 30mm
5. For an existing ac transmission line, the string efficiency is 80%. If dc voltage is supplied for the same set up, the string efficiency will be
- <80%
- 80%
- 90%
- 100%
6. In a string of suspension insulators, the voltage distribution across the different units of a string could be made uniform by the use of a grading ring, because it
- forms capacitances with link-pins to carry the charging currents from link-pins to earthed structure
- forms capacitances which help to cancel the charging current from link-pins
- increase the capacitances of lower insulator units to cause equal voltage drop
- decrease the capacitances of upper insulator units to cause voltage drop
7. A moving coil voltage regulator consists of a laminated magnetic core carrying
- Two coils similarly placed on the core and connected in series along with an open- circuited third coil
- Two oppositely wound coils and a third short-circuited coil fixed on the core with respect to the first two coils
- Two oppositely wound coils arid a third coil short-circuited that can be moved mechanically along the core
- Two coils similarly placed on the core connected in series with a third coil open- circuited which moves along the core mechanically
8. A generator is connected to an infinite bus through a double circuit transmission. The fault occurring at the middle of one of the transmission lines is subsequently cleared by opening the circuit breakers at both the ends of the line simultaneously. The transient stability limit of the system is improved by
- Decreasing the excitation of generator
- Decreasing the fault-clearing time
- Increasing the fault-clearing time
- Increase the transfer reactance between the generator and infinite bus
9. The velocity of travelling wave through a cable of relative permittivity 9 is
- 9 x 108 m /s
- 3 x l08 m /s
- 108m /s
- 2 x 108 m/s
10. The bus admittance matrix (Y bus) of a power system is not
- Symmetric
- A square matrix
- A full matrix
- Generally having dominant diagonal elements