Ques 41. In a 3-phase voltage source inverter used for speed control of induction motor, antiparallel diodes are used across each switching device. The main purpose of diodes is to:
- Protect the switching devices against overvoltage
- Provide the path for freewheeling current
- Allow the motor to return energy during regeneration✓
- Help in switching off the devices
Ques 42. Skewing of rotor bars eliminates the:
- Effect of space harmonics✓
- The entire effect of crawling
- Magnetic noise
- Vibration due to unequal force developed on the rotor
Ques 44. The steady-state fault current during a 3 phase terminal fault on a generator is determined by:
- The transient reactance of the generator
- The Sub-transient reactance of the generator
- The synchronous reactance of the generator✓
- DC offset during the instant of the fault
Ques 45. A 3-phase delta-connected squirrel cage induction motor when started with a DOL starter has a starting torque of 600 NM. Its starting torque when the star-delta starter is used:
- 600 NM.
- 200 NM✓
- 300 NM
- 1200 NM
Ques 48. Making current of a circuit breaker refers to:
- Steady-state rated current
- Average value of transient short circuit current
- R.M.S. value of the short-circuit current at the time of major peak✓
- Equal to the fault current
Ques 49. In case of a ‘High Voltage DC’ transmission, how many minimum conductors are required?
Ques 50. Which of the following motor has squirrel-cage winding on the stator?
- 3 phase squirrel cage induction motor
- Single-phase squirrel cage pump motor
- Single-phase ceiling fan induction motor✓
- Single-phase table fan induction motor
In conventional ceiling fans, a single-phase induction motor is used. These motors consume minimum power and hence, are also known as fractional kilowatt motors. The rotor in the single-phase induction motor is of squirrel cage rotor type. A single-phase induction motor requires only one power phase for operation. It converts the electrical energy from the power input into mechanical energy.