Power Electronics Basic Interview Questions : Set-4

Power Electronics Basic Interview Questions with Answers:

In this post we are going to discuss about various Power Electronics Basic Interview Questions with brief answers...In this set, we will focus on Electrical Drives related questions...Before proceeding further we will give few tips to you...
[1] You may be visit here to prepare for the interview, for a company who involves industrial automation, motor control etc...
[2] What do you think, that  the interviewer will expect from you?
He needs a candidate who has a basic knowledge of various DC and AC motors and understanding the operation of various special motors...
We had given various drives related interview questions here...

[Q] What is meant by Electrical Drives?
Answer: Systems employed for motion control are called as "Drives" and many employ any of the prime movers such as, diesel or petrol engines, gas or steam turbines, hydraulic motors and electric motors for supplying mechanical energy for motion control. Drives employing electric motors are known as " electric drives".

Here, We had given only the definition of electrical drive. But if you face this question in the face to face interview try to explain in detail. Draw the Block diagram of the electrical drive first. During the time, you recall about the basics and every part of the electrical drive system and explain as detail as possible. Click here to know about Electrical Drives basics and types

[Q] What are the different factors for the selection of electrical drives?
Steady state operation requirements
Transient operation requirements
Requirements related to the source
Capital and running cost, maintenance needs, life
Space and weight restrictions
Environment and location

[Q] What are the parts of electrical drives?
Electrical motors and load
Power Modulator
Control Unit
Sensing unit

[Q] What are modes of operation of electrical drives?
Steady state 
Acceleration including starting
Deceleration including stopping

[Q] What is meant by four quadrant operation?
A motor operate in two modes-motoring and braking. In motoring, it converts electrical energy into mechanical energy, which supports its motion. In braking, it works as a generator converting mechanical energy into electrical energy, and thus, opposes the motion. Motor can provide motoring and braking operations for both forward and reverse directions.

[Q] What is meant by regenerative braking?
Regenerative braking occurs when the motor speed exceeds the synchronous speed. In this case, the induction motor would run as the induction generator is converting the mechanical power into electrical power, which is delivered back to the electrical system. This method of braking is known as regenerative braking.

[Q] What is the function of the free wheeling diode in a phase controlled rectifier?
To improve input power factor
To make the load current continuous

[Q] What is meant by chopper?
Chopper converts fixed dc voltage into variable dc voltage

[Q] What is brushless DC motor?
An inverter fed trapezoidal permanent magnet AC motor drive operating in self-controlled mode is called brushless dc motor.

[Q] What is a PMSM?
PMSM = Permanent Magnet Synchronous Motor. In medium and small size synchronous motors dc field can be produced by permanent magnets.

[Q]Classification of PMSM?
According to construction
1. Surface mounted PMSM
2. Interior mounted PMSM
According to the nature of voltage induced
1. Sinusoidally excited
2. Trapezoidally excited

[Q] What is the basic principle of an electric generator?
A basic principle of an electric generator is based on Faraday's law of electromagnetic induction. ie, whenever a conductor is moved in the magnetic field, dynamically induced emf is produced in the conductor.

[Q] What is the purpose of yoke in a dc machine?
It acts as a protected cover for the whole machine and provides mechanical support for poles. It carries the magnetic flux produced by the poles. The flux per pole divides at the yoke, so that the yoke carries only half the flux produced by each pole.

[Q] What is th purpose of interpoles in modern dc machine?
In modern dc machines, commutating poles or interpoles are provided to improve the commutation process.

[Q] Why the armature poles are made of laminations?
Because to reduce the eddy current losses.

[Q] What are the different types of DC generator?
Separately excited dc generator
Self excited dc generator
- Series generator
- Shunt generator
- Compound generator
1. Long shunt compound
2. Short shunt compound

[Q] Define armature reaction...
The term armature reaction means the effect of the mmf set up by the armature current on the distribution of mmf under main poles of a dc machine.

[Q] What are the main effects of armature reaction?
Due to armature reaction:
(1) The main field flux gets weakened or gets demagnetized. This effect is called Demagnetization effect.

(2) The main field flux gets distorted. This effect is called Cross-magnetization effect.

We believe that these Power Electronics Basic Interview Questions will help for your interview preparation... Please leave your comments below...

Read more Power Electronics Basic Interview Questions in the following posts
Power Electronics Interview Questions: Set-1
Power Electronics Technical Interview Questions: Set-2
Power Electronics Basic Interview Questions: Set-3

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11 Responses



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