Electrical Engineering Questions

1)  If step down transformer step down the voltage,will current will also be proportional step up. If yes then how transformer handle such a large current?
Answer :

Transformer works on the principle that,I1V1 = I2V2 at all times.where I1V1 are primary current and voltage respectively; I2V2 are the corresponding secondary current and voltage respectively. From the above equation, if you step- down the voltage the current must increase to maintain the equality and vice versa. Based on this principle, the makers of transformers ensure that the gauge of copper wire used in the LV-winding can withstand the current together with tolerance.

2) Why generator is not connecting in delta ..why connecting in star ?

Answer : 

In star connection voltage/phase=line voltage/1.73 and emf induced in generator is directly proportional to number of turns. So in star connection we have to use less number of turns & insulation.star connection is most economical than delta

3) What is a doble test?

Answer :

The insulating power factor test, better known as the ”DobleTest”, is a complete overall test of the insulating properties of a transformer. Elements such as carbonization, ionization, moisture, and heat can breakdown the insulation's strength. The Doble test measures the power losses due to leakage current through the insulation.

4) How i measured Bus bars weight without wighting ?

Answer :

take the thickness of the busbar material ,length and the density of the material.Then materiual volume = Thickness X length.then weight = Volume x density of the busbar material(say Al or copper).

5) why there is a humming noise in transformer?

Answer :

Basically, we used ferromagentic material in core...when magnetic flux linked with thid core..thier is some physically expand and contract slightly with each cycle of the magnetic field...and that effect known as magnetostriction..(Magnetostriction is a property of ferromagnetic materials that causes them to change their shape or dimensions during the process of magnetization... it was first identified in 1842 by James Joule when observing a sample of nickel)...due to this effect causes fluctuating forces between the primary and secondary windings. These incite vibrations within nearby metalwork, adding to the humming noise, and consuming a small amount of power.