Friday, March 20, 2009

Electrical Interview questions Part 4

Q:What will happen when power factor is leading in distribution of power?
A:If their is high power factor, i.e if the power factor is close to one:
1.losses in form of heat will be reduced,
2.cable becomes less bulky and easy to carry, and very
cheap to afford, &
3. it also reduces over heating of tranformers.

Q:whats the one main difference between UPS & inverter ? And electrical engineering & electronics engineering ?
A:uninterrupt power supply is mainly use for short time . means according to ups VA it gives backup. ups is also two types : on line and offline . online ups having high volt and amp for long time backup with with high dc voltage.but ups start with 12v dc with 7 amp. but inverter is startwith 12v,24,dc to 36v dc and 120amp to 180amp battery with long time backup.

Q:What is 2 phase motor?
A:A two phase motor is a motor with the the starting winding and the running winding have a phase split. e.g;ac servo motor.where the auxiliary winding and the control winding have a phase split of 90 degree.

Q:Advantages of vvvf drives over non vvvf drives for EOT cranes?
A:1.smooth start and stop. jerking of load.
3.exact posiitoning
4.better protection for motor.
5.high/low speed selection.
6.reliability of break shoe.
7.programmable break control.
8.easy circutry
9.reduction in controls
10.increases motor life

Q:What is the significance of vector grouping in Power Transformers?
A:Every power transformer has a vector group listed by its manufacturer. Fundamentally it tells you the information about how the windings are connected (delta or wye) and the phace difference betweent the current and voltage. EG. DYN11 means Delta primary, Wye Secondry and the current is at 11 o clock reffered to the voltage.

Q:Which type of A.C motor is used in the fan (ceiling fan, exhaust fan, padestal fan, bracket fan etc) which are find in the houses ?
A:Its Single Phase induction motor which mostly squirrel cage rotor and are capacitor start capacitor run.