Induction motors are AC electrical motors that convert ac electrical energy to mechanical energy. The motors are named so because rotor voltage is induced in rotor windings instead of using physical wires. Induction motors are robust, highly efficient, reliable, and cost-effective motors. Because of their simplicity and durability, they are a popular choice for various industrial, commercial, and domestic applications. Unlike other motors, induction motors have no brushes or contacts that can wear out over time, making them less prone to failure and requiring minimal maintenance. They are also highly efficient, with power losses typically less than 5%, making them an environmentally friendly and cost-effective option. In this post Electrical Engineering Online shares Objective Electrical MCQ Questions on Earthing and Grounding.
Which of the below mentioned is not a component of an induction motor
Which of the below mentioned is not a component of an induction motor?
- Rotor
- Stator
- Commutator
- Bearings
Correct Answer: 3. Commutator
Explanation: Induction motors do not have a commutator. The commutator is typically found in DC motors.
The rotating magnetic field in an induction motor is produced by
The rotating magnetic field in an induction motor is produced by:
- Stator windings
- Rotor windings
- Both stator and rotor windings
- Permanent magnets
Correct Answer: 1. Stator windings
Explanation: The stator windings of an induction motor produce a rotating magnetic field that interacts with the rotor to induce current and create torque.
The slip of an induction motor is defined as
The slip of an induction motor is defined as:
- The difference between the synchronous speed and rotor speed
- The difference between the stator frequency and rotor frequency
- The difference between the number of stator poles and the number of rotor poles
- The difference between the number of stator windings and the number of rotor windings
Correct Answer: 1. The difference between the synchronous speed and rotor speed
Explanation: Slip is the difference between the synchronous speed of the rotating magnetic field and the actual speed of the rotor.
The slip speed of an induction motor is maximum when
The slip speed of an induction motor is maximum when:
- The motor is running at synchronous speed
- The motor is at standstill
- The motor is running at rated speed
- The motor is overloaded
Correct Answer: 2. The motor is at standstill
Explanation: The slip speed is the difference between the synchronous speed and the actual rotor speed. It is maximum when the motor is at standstill (not rotating).
Which type of rotor is commonly used in squirrel cage induction motors
Which type of rotor is commonly used in squirrel cage induction motors?
- Wound rotor
- Squirrel cage rotor
- Salient pole rotor
- Permanent magnet rotor
Correct Answer: 2. Squirrel cage rotor
Explanation: Squirrel cage rotors are the most commonly used rotors in induction motors due to their simplicity and robustness.
The starting current of an induction motor is typically
The starting current of an induction motor is typically:
- High
- Low
- Equal to the rated current
- Zero
Correct Answer: 1. High
Explanation: Induction motors draw a high starting current, often several times the rated current, during the starting period.
The power factor of an induction motor can be improved by
The power factor of an induction motor can be improved by:
- Increasing the supply voltage
- Decreasing the rotor resistance
- Adding capacitors to the circuit
- Increasing the rotor inductance
Correct Answer: 3. Adding capacitors to the circuit
Explanation: Adding capacitors in parallel with the induction motor can improve the power factor
The efficiency of an induction motor is highest at
The efficiency of an induction motor is highest at:
- Full load
- Half load
- No load
- Overload
Correct Answer: 1. Full load
Explanation: The efficiency of an induction motor is typically highest at or near its full load operating condition.
The concept of slip is applicable to
The concept of slip is applicable to:
- Synchronous motors only
- Induction motors only
- Both synchronous and induction motors
- DC motors only
Correct Answer: 2. Induction motors only
Explanation: Slip is a characteristic of induction motors and refers to the difference between the synchronous speed and rotor speed.
Which type of induction motor is commonly used in household appliances
Which type of induction motor is commonly used in household appliances?
- Single-phase induction motor
- Three-phase induction motor
- Synchronous motor
- Wound rotor motor
Correct Answer: 1. Single-phase induction motor
Explanation: Single-phase induction motors are commonly used in household appliances such as fans, refrigerators, and washing machines.
The torque-speed characteristics of an induction motor are
The torque-speed characteristics of an induction motor are:
- Linear
- Exponential
- Parabolic
- Hyperbolic
Correct Answer: 4. Hyperbolic
Explanation: The torque-speed characteristics of an induction motor are hyperbolic, meaning that as the speed increases, the torque decreases.
The term “slip frequency” refers to
The term “slip frequency” refers to:
- The frequency of the rotor current
- The difference between the stator and rotor frequencies
- The frequency of the applied voltage
- The frequency of the stator magnetic field
Correct Answer: 2. The difference between the stator and rotor frequencies
Explanation: Slip frequency is the difference between the electrical frequency of the stator winding and the electrical frequency of the rotor.