NPGCL Interview Question for passing JOB test of NPGCL easily by preparing the following question below
Generator k exciter ko DC kahan sy dety hn.
Oil kis liye use hota hy Transformermain?
Buch’holz Relay kia hoti hy kistrha,kia kaam krti hy.
SilicaGel kyun use hoti hy.
SilicaGel Moisture kidr syExtract krti hy.
Commutative aur Differential Generator main kia faraq hota hy?
Switchyard?
What is Lightning Arr ester?
Tube light
Filament of Bulb is made of Tungsten
What is power Triangle?
S=P+j Q
Reactive Power
Why We Need Reactive Power:
Vector Diagram of Transformer
Two transformer shaving different vector group can share power?
Purification level of Hydrogen for Generator Cooling
Run-away speed
Battery charging units Cooling method of transformer Corona
Circuit breakers,types,tests
Operating Principle
Two contacts called elector remainders closed under normal operating conditions.When fault occurs
on any part of the system,the trip coil of the circuit breaker get energized and contact are separated.
Classification Based on Voltage Range:
1.Low voltage CB(less than 1kv)
2.Medium voltage CB(1-52kv)
3.High voltage CB(66-220kv)
4.Extra high voltage CB(300-765kv)
5.Ultra high voltage CB(above 765kv)
Oil Circuit Breaker
• It is inflammable and there is a risk of fire.
• It may for man explosive mixture with air.
• It requires maintenance.
• Absorbs moisture,so dielectric strength reduces.
• Oil leakage problem.
• Oil has to be replaced after some operations because of the carbonation of oil.
Vacuum Circuit Breaker
• Compact,reliable and have longer life.
• No fire hazards.
• No generation of gas during and after operation.
• Can interrupt any fault current.
• No noise is produced while operating.
• Require less power for control operation.
SF6 Circuit Breaker
1.SF6 is an electro-negative gas.
2.It has strong tendency to absorb electrons.
3.When contact are opened in a high pressure flow of SF6 gas,arc produced.
4.Free electron in the arc are captured by the gas.Which build up enough insulation strength to extinguish arc.
5.it is much effective for high power and high voltages services,
6.SF6 gas is non flammable,nontoxic&chemical inert gas.
7.Maintenance free C.B.
Advantages Of SF6 Over Oil Circuit Breakers
• Short arc ing time
• Can interrupt much larger currents
• Gives noise less operation due to its closed gas circuit
• No moisture problem
• No risk of fire
• No carbon deposits. So no tracking and insulation problems
• Low maintenance cost
Circuit Breaker Testing
Minimum Pick-up Test
> Indicates the lowest voltage to operate the trip or close coil
>Ramp the voltage pulse until minimum voltage is reached with which the circuit breaker switches
Contact Resistance Test
> Test is performed with aµOhm-Meter
> Inject a high current
> Measurement of as mall voltage in a noisy environment
Timing Test
Timing under voltage condition
> Coils are normally driven by station battery
> What happens if battery condition is not the best
> Perform a test with reduced supply voltage(e.g.80%)
> Check times for under voltage
Motor Current
> Connects ource to charging motor or use current clamp
> Check charging times and charging currents
> Compare with previous measurements
Contact Travel
> Slow operation due to jammed mechanism
> Deterioration of mechanical damping
Dynamic Resistance Measurement
> Inject high current
> Start recording A &V
> Operate Circuit Breaker
> Calculate Resistance
Difference between arc and flash over
Flash over means ptaka maar jaana jab insulator k material ma koi khrabi hojati ha ya
phr uski surface par mitti/pani jama ho jata han.
Arc ka mtlb ha air ma sa current flow hona
What is universal motor?
What is compound motor?
Question about use of impedance relay
Effect of HVEHV lines on wireless communication
Dc generators and types
What is electrictraction and which motoris used
Which motor should be used on load
types of cb most used and which one is best
what is solenoid.
transformer tests
Grid components
Short cct test Open test Performance:
Heat Rate,
SCADA
Electrostatic or electro mechanical relay mn farq b pocha tha ek lar kay sy
excitation control b pocha.
polarization test of transformer*
can ddf test of transformer*
flourecentlampcanworkondcrnot*
substationkiyahy
*how generator work and paralleling of generator
*leading power factor benefits
*what is voltage and current
*what is bill.
stress on cable is high in which ac or dc and why stress more
protection of transformer and generator
reverse power relay for generator or turbine?
Types of motor winding and their usages
Relay types and working of SF6 relay
regenerative breaking,
difrence betwen MCB & MCCB,
SIL,BIL,
what is GIS insubstation,
thermo.couple,
dead end pole in distribution