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 Company >> KESC >> KESC Questions L&T Technical Test Questions (1) Simco Interview Questions (1)

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Question   3. What is Impedance Voltage in Transformer? Rank Answer Posted By
Interview Question Submitted By :: Sheik
I also faced this Question!!   © ALL Interview .com
```Impedencce voltage is nothing but self induced voltage in
reverse direction acting against the applied voltage( across
primary)
That is why after switching ON, the current intake reduces.```

1 Rvg

```Impedance voltage of a transformer is the voltage required
to

short circuit the secondary winding terminals of the
transformer and apply voltage gradually from zero at
primary winding.increase the voltage gradullay till the
full load current flows in the secondary.The voltage at
which full load current flows that voltage is the impedance
voltage of the transformer.This is required for short
circuit calculations.You can find on the transformer name
plate as Impedance voltage or percentage impedance.```

5 Ravi

```impedence voltage is that voltage which is applied through
primary side and full load current is flowing in secondary
side whwnever short Ckt. of secondary side```

0 Md.abul Basher

```can you say the formula for fine out short ckt current with
using impedance voltage```

0 Murali

```simply is Impedance voltage of a transformer is the
voltage drop in transformer,

voltage drop in transfermer,from primary to secondry
voltage. this i called impedence voltage of transfoermer```

```This is the voltage required to drive full load current in a
winding of a transformer when the other winding is short
circuited.
for example if percentage impedance of a 33/11kv transformer
is 6%. it means that 33x6/100=1.98KV would be required to
drive full load current in 33kv winding when 11kv winding is
short circuited.```

0 Shantanau Mishra

```It is the drop (&#949;) of a transformer:

&#949; =  Usc / Un  x   100  =  In / Isc   x   100

Un = nominated primer voltage

In = nominated secunder current

USc = primer voltage to obtain the In, when the secunder
side is short cicuited

Isc = secunder short circuited current```

0 István Galamb

```Impedance voltage of a transformer is the voltage required

to

short circuit the secondary winding terminals of the
transformer and apply voltage gradually from zero at
primary winding.increase the voltage gradullay till the

full load current flows in the secondary.The voltage at

which full load current flows that voltage is the impedance

voltage of the transformer.This is required for short
circuit calculations.You can find on the transformer name

plate as Impedance voltage or percentage impedance```

```Imedance voltage is the amount of voltage required on
primary side to produce rated current on secondry side of
transformer when secondry is short circuited.

Or
amount of voltage drop accros primary side when rated
current flows through it```

0 Gopal Birla

```Simply it is the percentage of the normal terminal voltage
required to circulate full-load current under short circuit
conditions, or can also be consider as the voltage drop of
the trafo..```

0 Naufal

```Simply,if 10% means voltage drop is 10% of open cct voltage

0 Hh

```it is % of rated primary voltage which require to establish
sufficient flux to produce full load current in short
circuited secondary, it is used while load loss test on
transformer.```

0 Sanjay Sharma

```The percentage impedance of a transformer is the volt drop
on full load due to the winding resistance and leakage
reactance expressed as a percentage of the rated voltage."

"It is also the percentage of the normal terminal voltage at
on side required to circulate full-load current under short
circuit conditions on other side."

The impedance of a transformer has a major effect on system
fault levels. It determines the maximum value of current
that will flow under fault conditions.

It is easy to calculate the maximum current that a
transformer can deliver under symmetrical fault conditions.
By way of example, consider a 2 MVA transformer with an
impedance of 5%. The maximum fault level available on the
secondary side is:

2 MVA x 100/5 = 40 MVA

and from this figure the equivalent primary and secondary
fault currents can be calculated.

A transformer with a lower impedance will lead to a higher
fault level (and vice versa).

The figure calculated above is a maximum. In practice, the
actual fault level will be reduced by the source impedance,
the impedance of cables and overhead lines between the
transformer and the fault, and the fault impedance itself.```

0 Manoj Kumar Tiwari

```Impedance voltage is calculated with short-circuit
test.which is very low compared to rated voltage. Impedance
voltage is the voltage which circulates the rated currents
when one of the two windings is shorted.```

0 Aravind Kumar

`Impedance voltage of a transformer is the measured voltage apply at primary winding while the secondary winding terminals of the transformer is short circuited and is increased gradually from zero till reach to full load current flows in the Primary. This voltage is much smaller than the transformer primary nominal voltage.`

0 Hussain

Question   Do you know how to joint the H.T and L.T Cables? Rank Answer Posted By
Interview Question Submitted By :: Ravi
I also faced this Question!!   © ALL Interview .com
`USING TRASFORMER`

0 Kavitha

```hi Kavitha can you give some details.

any one give some detailed and understanding answer.```

0 Debaroon Ray

`by using the FEVICOL(bcz iska jod sab se majhboot hai)`

0 Susanta

```hello dear,jointing the cable not by using transformer or
by fevicol,and its not a simple like  paper r wood jointing
by fevicol..
by using the heat strinkable method cable jointing will be
done,the heat strinking method gives high insulation to the
cable at jointing end,it can be used for jointing ht panel
board at the termination end,the kit used for the heat
strinkable is heavely insulation material,the joint will be
done by heating  material...
for jointing the  LT  to LT cable above 6
sqmm,10,16,35,50,70,90,120,150,185,240,300,400,sqmm cable
by jointing the FERRULE LUG between the cable joint by
using cripping tools and  then  insulation tape will be
rounded it heavely......```

0 Vinothbhabu

```ht cable connected with ht cricuit breaker(sf6)& LT cable
connected with ACB OR any other LT device.```

0 Sourav

```H.T cable joint can be done by two method.
By Heat shrink kit or by m seal kit.If cable is unearth
prefere to use heat shrink kit. in earth cable prefere to
use m seal kit.
Two L.T Cable joint done by m seal kit(low voltage kit)
and end termination done by bimatalic lugs.```

0 Dilip B Shah

```heat shrink joint is the best method. please check with
Rechem website.

No there is a new tehnology update that is Cold shrink
joint.```

0 Rvg.msceb

```HT  line tuns into LT  by  step down txr then connected lt
with LT  cable```

0 Sanjeet Swarnakar

```h.t. cables are joint by using h.v. straight througk joint
if it is cable and then heat shrink by using the
insulation .
l.t. cables are joint by using l.v. lugs and covered with
insulation and heat shrink or may be taken to H pole
structure to join with thimbles.```

0 Pravesh

```i agree with gobi but with little addition
•  reactive power Results from energy storage elements in
the power grid (mainly inductors and capacitors)
• Has a strong effect on system voltages
• It must balance in the grid to prevent voltage
problems
• Reactive power levels have an effect on voltage
collapse
so we need war compensation also to improve power factor...

so if it zero when get pure active power.but its not
possible in real as we have inductive & capacitive devices.```

0 Alpesh Surat

```Theoritically, you can joint HV & LV cable by using BUTT
Connector then mechanically crimp them and insulate, but for
practical application it is not possible because at High
Voltage Level, LV cable insulation will fail...```

0 Jeorge F. Nalugon

```I think The question itself little bit wrong,coz they are
asked the question HT & LT cables that means i just want to
understand whether its in Live or Dummy cables.if it is
live you cannot able to joit directly,it will happend
through transformer only by using Step up or Step
down.depends on the winding type,it can be desired.Primary
side if you can give HT[11KV],Secondary side you can get LT
[440V].```

0 Kuttivenu

```The question is itself creating confusion. Are you asking

0 Jyotirmaya Patra

```to joint these cableslike L.T. & H.T. cables there are many
componyes are providing the jointing kit for low tansion
cable in that kit some insulating material,lugs,earthing
wire, past to fill in joint are avable and instrction
manual also avable with kit. so we must read the jointing
procidure in the instruction manual & use this material to
joint the cable.```

0 Rajendra

```first we have to know why we need to join HT cable to LT
cable```

0 Jeeva

```you should not join h.t. & l.t. cables because both are used
for the different current rating & voltage rating.

1. for step up & step down the voltage you can connect to
the transformer.

2. for distribution you can connect to breaker.

or

if you are asking about jointing then it is not good but

1. you can joint by jointing kit. ( heat srinkeble ) as you
asked your cable is h.t & l.t  it 3-core & more than 25
SQ.MM  SO There is no other way to joint it.```

0 Mehul G. C.

```if we have to join h.v & l.v unreasonablybe have to make
straight britiania married joint.```

```HT cable are joint in tranceformer with Alluminiam Thimbles
& LT cable are joint with same. These all cables joint with
thimbles in HT & LT panal busbsr```

0 Mukesh Kumar Joshi

```i agree with gobi but with little addition vinothbhabu
in ht cable jonting one more jont is their that is compound
joint thid is also good method for ht cables```

0 Surya

`for cable joining splicing method is used i.e otdr equipement is used`

0 Sarvesham Nayar

```hi friends
ht and lt joints are not so easy
it need concentration and special care
first we should remove the area which was damaged
remove the sleeve and insulated material(ht cable)
use feruls and then crimp them with crimping tool
then use mastic tape to cover the feruls
next place the heat sink sleeves and heat them with
electric hot blower(hot air gun)```

0 Praveen

```HT to LT can't be joined directly. So, interface used for
interconnection is Transformer.```

0 Mukesh Kaushik

```h.t & l.t cable never jointable,due to different power
cables.```

0 Nasir Ahmed

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