Most important interview answer and question for EEE Part-Last-4

2. How can you start-up the 40w tube lite with
230v AC/DC without using any choke/Coil?
It’s possible by means of Electronic chokes,otherwise
it’s not possible to ionize the particles in tube light
with normal voltage.
3. What is “pu” in electrical engineering?
Pu stands for per unit and this will be used in single
line diagram of power distribution and it is like a
huge electrical circuit with no of components
(generators, transformers, loads) with different
ratings (in MVA and KV). To bring all the ratings into
common platform we use pu concept in which, in
general largest MVA and KV ratings of the
component is considered as base values, then all
other component ratings will get back into this
basis.Those values are called as pu values.
(p.u=actual value/base value).
5. Why link is provided in neutral of an ac circuit
and fuse in phase of ac circuit?
Link is provided at a Neutral common point in the
circuit from which various connection are taken for
the individual control circuit and so it is given in a
link form to withstand high Amps. But in the case of
Fuse in the Phase of AC circuit it is designed such
that the fuse rating is calculated for the particular
circuit (i.e load) only.So if any malfunction happen
the fuse connected in the particular control circuit
alone will blow off.
6. How tube light circuit is connected and how it
works?
A choke is connected in one end of the tube light and
a starter is in series with the circuit. When supply is
provided ,the starter will interrupt the supply cycle
of AC. Due to the sudden change of supply the chock
will generate around 1000volts . This volt will
capable of to break the electrons inside the tube to
make electron flow. once the current passes through
the tube the starter circuit will be out of part. now
there is no change of supply causes choke voltage
normalized and act as minimize the current.
7. whats is MARX CIRCUIT?
It is used with generators for charging a number of
capacitor in parallel and discharging them in
series.It is used when voltage required for testing is
higher than the available.
8. What is encoder, how it function?
An encoder is a device used to change a signal (such
as a bitstream) or data into a code. The code may
serve any of a number of purposes such as
compressing information for transmission or
storage, encrypting or adding redundancies to the
input code, or translating from one code to another.
This is usually done by means of a programmed
algorithm,especially if any part is digital, while most
analog encoding is done with analog
circuitry.
9. What are the advantages of speed control using
thyristor?
Advantages :1. Fast Switching Characterstics than
Mosfet, BJT, IGBT 2. Low cost 3. Higher Accurate.
10. Why Human body feel Electric shock ?? n in an
Electric train during running , We did nt feel any
Shock ? why?
Unfortunately our body is a pretty good conductor of
electricity, The golden rule is Current takes the
lowest resistant path if you have insulation to our
feet as the circuit is not complete (wearing rubber
footwear which doing some repairs is advisable as
our footwear is a high resistance path not much
current flows through our body).The electric train is
well insulated from its electrical system.
11. what is the principle of motor?
Whenever a current carrying conductor is placed in
an magnetic field it produce turning or twisting
movemnt is called as torque.
12. Why, when birds sit on transmission lines or
current wires doesn’t get shock?
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.
13. what is meant by armature reaction?
The effect of armature flu to main flux is called
armature reaction. The armature flux may support
main flux or opposes main flux.
14. what happen if we give 220 volts dc supply to d
bulb r tube light?
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.
15. Which motor has high Starting Torque and
Staring current DC motor, Induction motor or
Synchronous motor?
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.
16. what is ACSR cable and where we use it?
ACSR means Aluminium conductor steel reinforced,
this conductor is used in transmission & distribution.
17. What is vaccum currcuit breaker.define with
cause and where be use it Device?
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 kv.
18. What will happen when power factor is
leading in distribution of power?
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.
19. whats the one main difference between UPS &
inverter ? And electrical engineering &
electronics engineering ?
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 2v dc with 7
amp. but inverter is startwith 2v,24,dc to 36v dc and
20amp to 80amp battery with long time backup.
20. What is 2 phase motor?
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.
21. Advantages of vvvf drives over non vvvf
drives for EOT cranes?
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
22. What is the significance of vector grouping in
Power Transformers?
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. DYN means Delta primary,
Wye Secondry and the current is at o clock reffered
to the voltage.
23. 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 ?
Its Single Phase induction motor which mostly
squirrel cage rotor and are capacitor start capacitor
run.
24. Give two basic speed control scheme of DC
shunt motor?
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 .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.
25. what is the principle of motor?
Whenever a current carrying conductor is placed in
an magnetic field it produce turning or twisting
movement is called as torque.
26. what is meant by armature reaction?
The effect of armature flu to main flux is called
armature reaction. The armature flux may support
main flux or opposes main flux.
27. Give two basic speed control scheme of DC
shunt motor?
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 .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.
28. what is the difference between synchronous
generator & asynchronous generator?
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.
29. What is the Polarization index value ? (pi
value)and simple definition of polarization index
?
Its ratio between insulation resistance(IR)i.e meggar
value for 0min to insulation resistance for min. It
ranges from 5-7 for new motors & normally for
motor to be in good condition it should be Greater
than .5 .
30. Why syn. generators are used for the
production of electricity?
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.
31. What is the difference between synchronous
generator & asynchronous generator?
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.
32. 1 ton is equal to how many watts?
1 ton = 12000 BTU/hr and to convert BTU/hr to
horsepower, 12,000 * 0.000929 = 4.715 hp therefore 1
ton = 4.715*.746 = .5 KW.
33. why syn. generators r used for the production
of electricity?
synchronous machines have capability to work on
different power factor(or say different imaginary
pow varying the field emf. Hence syn. generators r
used for the production of electricity.
34. Enlist types of dc generator?
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
compound(which is further classified into
cumulative and differential).
35. What is Automatic Voltage regulator(AVR)?
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.
36. What is an exciter and how does it work?
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. initial
voltage is built up by residual magnetism.It gives the
starting torque to the generator.
37. Difference between a four point starter and
three point starter?
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
38. Why use the VCB at High Transmission System
? Why can’t use ACB?
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 .
39. What is the difference between surge arrestor
and lightning arrestor?
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.
40. What happens if i connect a capacitor to a
generator load?
Connecting a capacitor across a generator always
improves power factor,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.
41. Why the capacitors works on ac only?
Generally capacitor gives infinite resistance to dc
components(i.e., block the dc components). it allows
the ac
components to pass through.
42. Explain the working principal of the circuit
breaker?
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.
43. How many types of colling system it
transformers?
1. ONAN (oil natural,air natural)
2. ONAF (oil natural,air forced)
3. OFAF (oil forced,air forced)
4. ODWF (oil direct,water forced)
5. OFAN (oil forced,air forced)
44. What is the function of anti-pumping in circuit
breaker?
when breaker is close at one time by close push
button,the anti pumping contactor prevent re close
the breaker by close push button after if it already
close.
45. what is stepper motor.what is its uses?
Stepper motor is the electrical machine which act
upon input pulse applied to it. it is one type of
synchronous motor which runs in steps in either
direction instead of running in complete cycle.so, in
automation parts it is used.
46. How to calculate capacitor bank value to
maintain unity power factor with some suitable
example?
KVAR= KW(TAN(COS(-1)#e)- TAN(COS(-1)#d) )
#e= EXISTING P.F.
#d= DESIRED P.F.
47. Tell me in detail about c.t. and p.t. ?
(Company:reliance)
The term C.T means current transformer,and the
term P.T means potential transformer.In circuit
where measurements of high voltage and high
current is involved they are used there.Particularly
when a measuring device like voltmeter or ammeter
is not able to measure such high value of quantity
because of large value of torque due to such high
value it can damage the measuring device.so, CT and
PT are introduced in the circuits.
They work on the same principle of transformer,
which is based on linkage of electromagneticflux
produced by primary with secondary.They work on
the ratio to they are designed.E.g if CTis of ratio
50005A and it has to measure secondary current of
8000A.then ANS=8000*55000=8Aand this result will
be given to ammeter .and after measuring 8A we can
calculate the primary current.same is the operation
of PT but measuring voltage.
48. There are a Transformer and an induction
machine. Those two have the same supply. For
which device the load current will be maximum?
And why?
The motor has max load current compare to that of
transformer because the motor consumes real
power.. and the transformer is only producing the
working flux and its not consuming.. hence the load
current in the transformer is because of core loss so
it is minimum.
49. what is power factor? whether it should be
high or low? why?
Power factor should be high in order to get smooth
operation of the system.Low power factor means
losses will be more.it is the ratio of true power to
apparent power. it has to be ideally 1. if it is too low
then cable over heating & equipment overloading
will occur. if it is greater than 1 then load will act as
capacitor and starts feeding the source and will
cause tripping.(if pf is poor ex: 0.17 to meet actual
power load has to draw
more current(V constant),result in more losses if pf is
good ex: 0.95 to meet actual power load has to draw
less current(V constant),result in less losses).
50. What is the difference between Isolator and
Circuit Breaker?
Isolator is a off load device which is used for
isolating the downstream circuits from upstream
circuits for the reason of any maintenance on
downstream circuits. it is manually operated and
does not contain any solenoid unlike circuit breaker.