2011|Online electrical engineering & Electrical Interview Questions

Sunday, December 18, 2011


This post is about the HVDC Transmission Lines in India. I must thank Priya for asking electrical question regarding HVDC links.Hope it would be useful for the budding Electrical Engineers.Whenever we think about HVDC links,many questions comes to our mind.Some of them are 1.Why we should go for HVDC transmission instead of AC Transmission? 2.Does India has any HVDC links? If yes, how many and where are these HVDC links located ?

First of all,HVDC transmission is adopted whenever there is need for power transmission over longer distances.We must have heard the term "Break even Distance".It is the distance at which the cost for AC Transmission and the Cost for DC Transmission are equal.Usually it is around 600KM.Taking the distance, future requirements,cost saving and various other factors into considerations the HVDC links are set up.

To know the list of HVDC links in india click the below link.

Thursday, September 29, 2011


In web i came across a Electrical Question which says "Is it possible to make Electricity from the Ceiling fan?".The answer for this question is yes,you can make electricity using the ceiling fan.But Another question arises here,"Will the Output Electrical Energy from the fan would be more or equal to the supply given to the fan ?"

The answer for this question would be a definite NO.Let us see how the answer is justified.As we know that Energy can neither be created nor be destroyed.It is transformed from one form of energy to another form.The idea of placing a rotating magnet attached to the base of the fan and coils to the hook and try to generate electricity will not work out.

The reason for this is there will be a increase in the weight of the fan which would result in drawing more load current to run the fan at the same speed before attaching the rotor.So when input increases automatically efficiency comes down.Next having a magnet near the electrical wires would cause hysteresis loss and eddy current loss.Therefore if you sum up the output electrical energy and mechanical energy,it will be always less than your input electrical energy.

If you see renewable energy resources,the energy is taken as it is from the nature.For example,As the wind blows,we make use of it and we do not blow the wind and take electricity.In hydel power plants we use the potential energy stored in dams for generating electricity.So the idea of taking electricity from moving car,fan etc would be a failure.

Saturday, September 17, 2011


Hi itzme !!!.Please mention your name and also post your comments in latest post so that visitors can get a notice of the questions.Thanks for reading my blog and asking more questions.Hope my answers are useful to you.Next Electrical Engineering Question is "What is the use of Synchronous Generator?Which is more preferred synchronous/asynchronous alternators ?"

As the name indicates Synchronous generator runs at the synchronous speed.The relation for synchronous speed is given by,
Keeping the frequency of ouput voltage of the alternator as fixed, the synchronous speed changes based on the number of poles of the machine.For example,Our supply is 50 Hz.so for a 4 pole machine Ns would be 1500 rpm but for a 6 pole machine Ns would be 1000 rpm.

The synchronous alternator generates the output voltage at a constant frequency as the machine is made to run at synchronous speed.All the electrical appliances in our country are rated for 50 Hz,so the supply provided by electric board should be 50 Hz supply.Therefore synchronous alternators are more preferred than the asyncronous alternators.

In USA they use 60 Hz supply,so the machine's number of poles and synchronous speed will vary according to their frequency.

Friday, August 26, 2011


Hi guys.I am back !!! I apologize for posting the content after such a long time.A person has asked "Could you give an idea of which motors are being used in different appliances? and it is my pleasure to answer this Electrical Engineering question.Do you guys know in our mobile phone there is a motor.yes, it is used for vibration which is caused in the silent mode.These motors are called as vibration motors.

Next we will take the thing which we use very oftenly, PC's and Laptops.We use the Brushless DC motor fans for cooling the processor.In PC SMPS serves as the source for motor and in Laptop battery is the source for motors.Also the for CD drives we use the brushless motors.

In fans single phase Induction motors are used.In Mixer grinders and Grinders also we use single phase Induction motors only.But for the Grinders which has high capacities, we will be using 3 phase Induction motor up to 5HP motors.For traction,DC motors are used.The supply is high voltage single phase supply.AC supply is converted to DC using the Power Electronic Converters and are used to feed the DC motors.

Saturday, January 29, 2011


Here is the next question about the Fan Speed Regulator.
Will the power consumption  be same for normal regulator and electronic regulator at same speed ?
The answer to this would be no.The reason behind this is normal regulator uses resistances for the speed control of the fan.So the resistances will act as a potential divider,and the applied voltage to the fan changes the based on the resistance position.

At maximum speed the full voltage is applied.When the regulator position is decreased,resistance would be introduced and the voltage applied to the fan decreases which in turn reduces the speed of the fan.When the regulator position is kept at low speed, the power wastage across the resistance will be more.
Therefore the overall efficiency of the normal speed regulator is poor.

The electronic speed regulator uses the semi conductor devices.The voltage regulator is used to change the applied voltage to the fan.So the power loss is negligible in the electronic fan speed regulator.Therefore overall efficiency of the electronic regulator is high.


Hi guys...I am answering to one of the doubts posted in the comments section.This electrical question is regarding the Fan Speed Regulators.

1.What is the difference between electronic regulator and normal regulator in fan?
i) You would have noticed the old normal regulators in some old bungalows and some government buildings.Normal fan regulator is huge in size whereas electronic regulator is small in size with just a knob to control the speed.
ii) Speed variation is in steps in the normal regulators whereas in electronic speed regulators we can obtain smooth speed control.
iii) Normal fan speed regulators use resistances(works as potential divider network) for controlling the speed whereas the electronic speed regulator uses the voltage regulator which changes the input voltage to the fan thereby changing the speed of the fan.
iv) Heat dissipation is more in the normal fan speed regulators whereas in electronic regulators there is negligible heat dissipation.
v) Since the heat dissipation is more in the normal regulators, it will be provided with some holes at the sides for ventilation and are mounted outside the switch board.
vi) The electronic regulator will be mounted inside the switch board(the device) and only the control knob will be outside the switch board.

Monday, January 24, 2011


These are the most frequently asked Electrical Interview Questions from Transmission & Distribution.
During my interview, i said my area of interest is Transmission & Distribution.Then i was bombarded with the following questions.

Why do we go for higher voltage transmission lines?
There are many advantages in transmitting the power at high voltages.Because for the same power,the copper loss(I^2R loss) will be less for higher voltages,since power= V*I.There for current value decreases thereby decreasing the power loss.

Why do we prefer overhead transmission line over under ground transmission line?
  • The cost of the conductors used in over head lines in much lesser when compared to the under ground lines.
  • The under ground lines need perfect insulation so it is provided with extra insulation which increases the cost.
  • It is very difficult to identify and repair the faulty part in the under ground transmission lines.
  • Skin effect and Proximity effect are more in under ground lines than the Over head transmission lines.

Thursday, January 20, 2011


Hey friends..Let me share the Electrical Interview questions which i faced during my interviews.If you are attending interview for any software companies,the questions would be on basics of Electrical Engineering.

What is the difference between motor and generator ?
       Motor is an electrical device which converts electrical energy into mechanical energy where as Generator is an electrical device which converts mechanical energy to electrical energy.

What are the types of Motor and Generator?
        Basically both motors and generators are classified as DC and AC. 
Further DC motor is classified as DC Series motor,DC Shunt motor,DC Compound motor.
AC motor is classified as 1 phase motor and 3 phase motor and Synchronous motor.
There are special machines such as Brushless DC motor,Universal motor,Stepper Motor,Hysteresis motor.

DC generator as classified as separately exicited DC generator,DC Series generator,DC shunt generator,DC compound generator.AC generators are called as alternators.Alternators are single phase and three phase alternators.There is also Synchronous generator.

Thursday, January 6, 2011


In almost every electrical interview this question is asked "What is Current?".

Current is nothing but the movement of electric charge that occurs in a closed circuit.Flow of electrons is from negative terminal to positive terminal.The conventional current direction is opposite to the direction of electron flow.

In analogy terms,current is equivalent to water flow in a pipe.When pipe is closed there is no water flow and when it is opened there is a flow of water.Similarly when insulators are used in a circuit,it opposes current flow by arresting the movement of electrons and when a conductor is used in a circuit,it allows the current to flow through.