Electrical interview faqs Part 2

Electrical interview faqs Part 2
1)Why, when birds sit on transmission lines or current wires doesn't get shock?
Answer:Its true that if birds touch the single one line (phase or neutral) they don't get electrical shock... if birds touch 2 lines than the circuit is closed and they get electrical shock.. so if a human touch single one line(phase) then he doesn't get shock if he is in the air (not touching - standing on the ground if he is standing on the ground then touching the line (phase) he will get a shock because the ground on what we standing is like line (ground bed - like neutral)। and in the most of electric lines the neutral is grounded..so that means that human who touch the line closes the circuit between phase and neutral.
2)What is meant by armature reaction?
Answer:The effect of armature flu to main flux is called armature reaction. The armature flux may support main flux or opposes main flux.
3)What happen if we give 220 volts dc supply to d bulb r tube light?
Answer:Bulbs [devices] for AC are designed to operate such that it offers high impedance to AC supply. Normally they have low resistance. When DC supply is applied, due to low resistance, the current through lamp would be so high that it may damage the bulb element.
4)Which motor has high Starting Torque and Staring current DC motor, Induction motor or Synchronous motor?
Answer:DC Series motor has high starting torque. We can not start the Induction motor and Synchronous motors on load, but can not start the DC series motor without load.
5)What is ACSR cable and where we use it?
Answer:ACSR means Aluminium conductor steel reinforced, this conductor is used in transmission & distribution.
6)What is vaccum currcuit breaker.define with cause and where be use it Device?
Answer:A breaker is normally used to break a ciruit. while breaking the circuit, the contact terminals will be separated. At the time of seperation an air gap is formed in between the terminals. Due to existing current flow the air in the gap is ionised and results in the arc. various mediums are used to quench this arc in respective CB's. but in VCB the medium is vaccum gas. since the air in the CB is having vaccum pressure the arc formation is interrupted. VCB's can be used upto 11kv.
7)What will happen when power factor is leading in distribution of power?
Answer: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.
8)Whats the one main difference between UPS & inverter ? And electrical engineering & electronics engineering ?
Answer: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.
9)What is 2 phase motor?
Answer: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.
10)Advantages of vvvf drives over non vvvf drives for EOT cranes?
Answer:1.smooth start and stop.
2.no 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
11)What is the significance of vector grouping in Power Transformers?
Answer: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.
12)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 ?
Answer:Its Single Phase induction motor which mostly squirrel cage rotor and are capacitor start capacitor run.