September 2011|Online electrical engineering & Electrical Interview Questions

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 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.