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 L&T technical test questions  L&T Technical Test Questions (1)  Simco interview questions  Simco Interview Questions (2)
 
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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
Answer
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
 
 
Answer
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
 
 
Answer
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
 
 
 
Answer
can you say the formula for fine out short ckt current with
using impedance voltage
 
0 Murali
 
 
Answer
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
 
0 Ekanadam Patlavath
 
 
Answer
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
 
 
Answer
It is the drop (ε) of a transformer: 

ε =  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
 
 
Answer
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
 
0 Madhu
 
 
Answer
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
 
 
Answer
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
 
 
Answer
Simply,if 10% means voltage drop is 10% of open cct voltage 
at full load.
 
0 Hh
 
 
Answer
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
 
 
Answer
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
 
 
Answer
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
 
 
Answer
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
Answer
USING TRASFORMER
 
0 Kavitha
 
 
Answer
hi Kavitha can you give some details.

any one give some detailed and understanding answer.
 
0 Debaroon Ray
 
 
Answer
by using the FEVICOL(bcz iska jod sab se majhboot hai)
 
0 Susanta
 
 
Answer
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
 
 
Answer
ht cable connected with ht cricuit breaker(sf6)& LT cable 
connected with ACB OR any other LT device.
 
0 Sourav
 
 
Answer
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
 
 
Answer
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
 
 
Answer
HT  line tuns into LT  by  step down txr then connected lt 
with LT  cable
 
0 Sanjeet Swarnakar
 
 
Answer
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
 
 
Answer
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
 
 
Answer
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
 
 
Answer
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
 
 
Answer
The question is itself creating confusion. Are you asking
about the connection/jointing method,
 or are you askinmg about the connection between HT-LT voltage?
 
0 Jyotirmaya Patra
 
 
Answer
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
 
 
Answer
first we have to know why we need to join HT cable to LT 
cable
 
0 Jeeva
 
 
Answer
you should not join h.t. & l.t. cables because both are used
for the different current rating & voltage rating.

if you are asking about connection then 
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.
 
 
Answer
if we have to join h.v & l.v unreasonablybe have to make 
straight britiania married joint.
 
0 Anadi Sharma
 
 
Answer
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
 
 
Answer
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
 
 
Answer
for cable joining splicing method is used i.e otdr equipement is used
 
0 Sarvesham Nayar
 
 
Answer
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
 
 
Answer
HT to LT can't be joined directly. So, interface used for 
interconnection is Transformer.
 
0 Mukesh Kaushik
 
 
Answer
h.t & l.t cable never jointable,due to different power 
cables.
 
0 Nasir Ahmed
 
 
 
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