Top Interview Questions on Electric Motors
Electric motors are an essential component of every industry as they comprise hundreds or thousands of small devices to large industrial machinery. we discussed the importance of electric motors in an interview for electrical or industrial automation. Here are some of the frequently asked interview questions from motors with a few pointers to structure your answers.
1.What is an electric motor?
Answer: An electric motor is a machine that transforms electrical energy to mechanical energy. This works on the principle of magnetic field interaction with current-carrying conductors to produce rotary motion. Electric motor used in pump, compressor and other industrial application.
2.What are the main types of electric
Answer:
Electric motors can be divided into two major types:
AC Motors (Alternating Current Motors)
These motors work on alternate current and can be categorized into:
Synchronous Motors
Induction Motors
DC Motor (Direct Current motor)
This is an example for direct current motor, and these motors are powered by either DC battery or a rectifier circuit.
Brushed DC Motors
Brushless DC Motors
Stepper Motors
3.Explain the working principle of an induction motor.
Answer:
An induction motor works on the principle of electromagnetic induction. Stator windings dedicated on current A.C leads to a rotating magnetic field . As a result, magnetic field is generated in the rotor which drives current flow. The rotating magnetic field generated by the stator interacts with the rotor’s induced rotation magnetic field, therefore producing a force that rotates the rotor.
But the rotor does not rotate synchronously at the speed of the magnetic field produced by stator called synchronous speed. As a result, it is always slightly behind synchronous speed so the rotor gets to cut the lines of force and generate torque allowing the motor to produce work. This disparity in rotation speed is called “slip.”
4.What is the difference between a synchronous motor and an induction motor?
Synchronous Motor:
Operates at constant speed, synchronized to the frequency of AC supply.
Provides a magnetic field only when externally excited
Induction Motor:
Rotor speed is lower than synchronous speed.
It does not require any external excitation; the rotating magnetic field of the stator induces the current in the rotor.
5.What is the purpose of a commutator in a DC motor?
A commutator reverses the rotor winding current in a DC motor. This makes sure that whatever torque is acting on the rotor will always in one direction and thus continuous rotation. carbon brushes together with commutator keep the motor spinning.
6.What is the slip in an induction motor?
slip represents the difference between the motor’s synchronous speed for its magnetic field and actual rotor speed. Usually it is given as a percentage of synchronous speed. One must note that Slip is an input to a motor, it helps create torque in the motor and is one of the key parameters for induction motors.
7.What are the losses in an electric motor?
Copper Losses (I²R losses): Resulting from winding resistances.
Iron Losses (Core Losses): which include hysteresis and eddy current losses in the motor core.
Mechanical Losses: Friction in bearings and air resistance (windage losses).
Stray Load Losses: It is caused due to non-idealities in the magnetic circuit of a motor and leakages fields.
8.How can the efficiency of an electric motor be improved?
To minimize copper and iron losses: By using quality materials
Better design : right winding design, no air gaps.
Efficient Control Techniques: Like Variable Frequency Drives (VFDs) for motor speed and load control.
9.What is the function of a capacitor in a single-phase induction motor?
Single-phase induction motors use a capacitor to create a phase shift of the currents in the main and auxiliary windings. The phase shift creates a rotating magnetic field, which in turn aids the motor starting and running. Capacitors: They are normally used in capacitor-start or run motors to enhance the starting torque and running performances.
10.What is a stepper motor, and where is it used?
Stepper motor is a type of DC motors with discrete steps instead of continuous motion. The motor is controlled by electric pulses, which each pulse will cause a fixed angle of movement. Stepper motors are common in precision applications including 3D printers, CNC machines, and robotics.
11.How do you reverse the direction of a motor?
Answer:
For AC Motors:
Reverse two of the three-phase connections in a 3 phase motor
For a single-phase motor by reversing the connections to the start winding or auxiliary winding will reverse direction.
For DC Motors:
Reverse the polarity of the supply voltage..
12.What is a universal motor, and where is it used?
Universal Motor: A universal motor is a type of motor that runs on both AC and DC power. It is like a DC series motor, and it is very popular for use in household devices such as blenders, vacuum cleaners and power tools due to its speed capability and ability to operate on either AC or DC.
13.What is torque, and how is it related to motor performance?
The rotating force that comes out of the shaft of a motor. It has a direct relation to the work done by a motor. Motor torque is dependent on the current through the motor windings, strength of magnetic field (often permanent magnets), and motor design.
14.What is a servo motor, and where is it used?
The servo motor is a type of motor used for precise control of position, speed and torque. The system include the feedback that regulates motor output to meet expectation control input. Used in robotics, CNC machinery, and automated manufacturing systems.]
15.How does a Variable Frequency Drive (VFD) control motor speed?
Variable Frequency Drive (VFD) is an electronic device to adjust the speed of a motor, by varying its input frequency and voltage. Thus changing the motor’s speed to save energy and avoid inefficient operation of motors under different loading conditions.
Conclusion
So, if you are applying for an industrial automation, electrical engineering or related jobs then preparing questions based on electric motors is vital. Grasping the basics of how electric motors function, their varieties and applications will help you ace both technical interviews with strides.