Electrical interview question: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.
Electrical interview question: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.
Electrical interview question: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.
Electrical interview question: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
Electrical interview question: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.
Electrical interview question: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.
Electrical interview question:Give two basic speed
control scheme of DC shunt motor?
Answer:1. By using flux control method:in this method a
rheostat is connected across the field winding to control the field current.so
by changing the current the flux produced by the field winding can be changed,
and since speed is inversely proportional to flux speed can be controlled
2.armature control method:in this method a rheostat is connected across
armature winding by varying the resistance the value of resistive drop(IaRa)can
be varied,and since speed is directly proportional to Eb-IaRa the speed can be
controlled.
Electrical interview question:what is the principle of
motor?
Answer:Whenever a current carrying conductor is
placed in an magnetic field it produce turning or twisting movement is called
as torque.
Electrical interview question: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.
Electrical interview question:Give two basic speed
control scheme of DC shunt motor?
Answer:1. By using flux control method:in this method a
rheostat is connected across the field winding to control the field current.so
by changing the current the flux produced by the field winding can be changed,
and since speed is inversely proportional to flux speed can be controlled
2.armature control method:in this method a rheostat is connected across
armature wdg.by varying the resistance the value of resistive drop(IaRa)can be
varied,and since speed is directly proportional to Eb-IaRa the speed can be
controlled.
Electrical interview question:what is the difference
between synchronous generator & asynchronous generator?
Answer:In simple, synchronous generator supply's both
active and reactive power but asynchronous generator(induction generator)
supply's only active power and observe reactive power for magnetizing.This type
of generators are used in windmills.
Electrical interview question:What is the Polarization
index value ? (pi value)and simple definition of polarization index ?
Answer:Its ratio between insulation resistance(IR)i.e
meggar value
for 10min to insulation resistance for 1 min. It ranges from 5-7
for new motors & normally for motor to be in good condition it should be
Greater than 2.5 .
Electrical interview question:Why syn. generators r used
for the production of electricity?
Answer:synchronous machines have capability to work on
different power factor(or say
different imaginary power varying the field emf. Hence syn. generators r
used for the production of electricity.
Electrical interview question:What is
the difference between synchronous generator & asynchronous
generator?
Answer:In simple, synchronous generator supply's both
active and reactive power but asynchronous generator(induction generator)
supply's only active power and observe reactive power for magnetizing.This type
of generators are used in windmills.
Electrical interview question:1 ton is equal to how many
watts?
Answer:1 ton = 12000 BTU/hr and to convert BTU/hr to
horsepower,
12,000 * 0.0003929 = 4.715 hp therefore 1 ton = 4.715*.746 = 3.5 KW.
Electrical interview question:why syn. generators r used
for the production of electricity?
Answer:synchronous machines have capability to work on
differentpower factor(or say
different imaginary pow varying the field emf. Hence syn. generators r used
for the production of electricity.
Electrical interview question:Enlist types of dc generator?
Answer:D.C.Generators are classified into two types
1)separatly exicted d.c.generator 2)self exicted d.c.generator, which is
further classified into;1)series 2)shunt and
3)compound(which is further classified into cumulative and differential).
Electrical interview question:What is
Automatic Voltageregulator(AVR)?
Answer:AVR is an abbreviation for
Automatic Voltage Regulator.It is important part in Synchronous
Generators, it controls theoutput voltage of the generator by
controlling its excitation current. Thus it can control the output Reactive
Power of the Generator.
Electrical interview question:What is an exciter and how
does it work?
Answer:There are two types of exciters, static exciter and
rotory exciter.purpose of excitor is to supply the excitation
dc voltage to the fixed poles of generator.Rotory excitor is an
additional small generator mounted on the shaft of main generator. if it is dc
generator, it will supply dc to the rotory poles through slip ring and brushes(
conventional alternator). if it is an ac excitor, out put of ac excitor is
rectified by rotating diodes and supply dc to main fixed poles.ac excitor is
the ac generator whose field winding are stationary and armature rotates.
initialvoltage is built up by residual magnetism.It gives the starting
torque to the generator.
Electrical interview question:Difference between a
four point starter and three point starter?
Answer:The shunt connection in four point stater is
provided separately form the line where as in three point stater it is
connected with line which is the drawback in three point stater
Electrical interview question:Why use the VCB at High
Transmission System ? Why can't use ACB?
Answer:Actually the thing is vacuum has high arc queching
property compare to air because in VCB ,the die electric strengths equal to 8
times of air . That y always vaccum used as inHT breaker and air used as in LT
.
Electrical interview question:What is
the difference between surge arrestor and lightning arrestor?
Answer:LA is installed outside and the effect of
lightning is grounded,where as surge arrestor installed inside panels
comprising of resistors which consumes the energy and nullify the
effect of surge.
Electrical interview question:What happens if i connect a
capacitor to a generator load?
Answer:Connecting a capacitor across a generator always
improves powerfactor,but it will help depends up on the engine capacity of the
alternator,other wise the alternator will be over loaded due to the extra watts
consumed due to the improvement on pf. Secondly, don't connect a
capacitor across an alternator while it is picking up or without any other
load.
Electrical interview question:Why the capacitors works on
ac only?
Answer:Generally capacitor gives infinite resistance to dc
components(i.e., block the dc components). it allows the ac components to pass
through.
Electrical interview question:Explain the working principal
of the circuit breaker?
Answer:Circuit Breaker is one which makes or breaks the
circuit.It has two contacts namely fixed contact & moving contact.under
normal condition the moving contact comes in contact with fixed contact thereby
forming the closed contact for the flow of current. During abnormal &
faulty conditions(when current exceeds the rated value) an arc is produced
between the fixed & moving contacts & thereby it forms the open
circuitArc is extinguished by the Arc Quenching media like air, oil, vaccum
etc.
Electrical interview question:How many types of colling
system it transformers?
Answer:1. ONAN (oil natural,air natural)
2. ONAF (oil natural,air forced)
3. OFAF (oil forced,air forced)
4. ODWF (oil direct,water forced)
[V1] 5. OFAN (oil forced,air forced)
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