ALLInterview.com :: Home Page            
 Advertise your Business Here     
Browse  |   Placement Papers  |   Company  |   Code Snippets  |   Certifications  |   Visa Questions
Post Question  |   Post Answer  |   My Panel  |   Search  |   Articles  |   Topics  |   ERRORS new
   Refer this Site  Refer This Site to Your Friends  Site Map  Bookmark this Site  Set it as your HomePage  Contact Us     Login  |  Sign Up                      
Google
   
 
Categories >> Engineering >> Electrical Engineering
 
 


 

 
 Civil Engineering interview questions  Civil Engineering Interview Questions (3072)
 Mechanical Engineering interview questions  Mechanical Engineering Interview Questions (3287)
 Electrical Engineering interview questions  Electrical Engineering Interview Questions (13322)
 Electronics Communications interview questions  Electronics Communications Interview Questions (2362)
 Chemical Engineering interview questions  Chemical Engineering Interview Questions (416)
 Aeronautical Engineering interview questions  Aeronautical Engineering Interview Questions (77)
 Bio Engineering interview questions  Bio Engineering Interview Questions (17)
 Metallurgy interview questions  Metallurgy Interview Questions (79)
 Industrial Engineering interview questions  Industrial Engineering Interview Questions (163)
 Instrumentation interview questions  Instrumentation Interview Questions (2375)
 Automobile Engineering interview questions  Automobile Engineering Interview Questions (106)
 Mechatronics Engineering interview questions  Mechatronics Engineering Interview Questions (38)
 Marine Engineering interview questions  Marine Engineering Interview Questions (43)
 Power Plant Engineering interview questions  Power Plant Engineering Interview Questions (75)
 Engineering AllOther interview questions  Engineering AllOther Interview Questions (1195)
Question
What is the difference between sensitive earth fault and 
restricted earth fault in power transformers?
 Question Submitted By :: Electrical-Engineering
I also faced this Question!!     Answer Posted By  
 
Answer
# 1
Sensitive Earth fault protection: Normally used on systems
where the earth fault current is limited to a very low
value. Scheme consists out of a ring CT (Core Balance CT)
around the three phase conductors, and the relay connected
to the secondary side of the CT. A very low setting is
possible, even sometimes lower then 1% FLA. Need to
coordinate with similar relays downstream. This method is
based on primary current vector addition or flux summation.
The conductor
cables pass through the center hole of the core balance CT.
Secondary current is the system zero-sequence current
3I_0.This scheme provides increased sensitivity with no
false residual currents. However,
care must be taken to prevent false tripping from unbalanced
inrush currents that may
saturate the current transformer core.

residual Earth Fault Relay:Restricted Earth Fault Protection
Is a type of zone of protection, or a differential scheme.
You get two types, low impedance and high impedance. Low
impedance is normally current operated and high impedance
voltage operated. High impedance REF is the most commonly
used. Relay connected in parallel with three phase CTs and
one neutral CT. It will look just for faults inside the
transformer, and need not to coordinate with relays
downstream (can operate very fast). With this kind of
protection you can protect over 90% transformer windings.
Need to use special class CTs, previously called class X
CTs.low impedance REF, are incorporated into some the new
microprocessor relays.
 
Is This Answer Correct ?    17 Yes 1 No
Raghavendran
 
Answer
# 2
A Restricted Earth Fault (R.E.F.) has nothing to do with the
magnitude of the current. It is in fact a normal earth fault
that is restricted to a 'zone'. That is, the R.E.F.
protection is only looking for earth faults occuring in a
given zone. Any earth fault outside the zone (restricted
area) is ignored by the R.E.F. protection. It is typically
used on power transformers, with the protected zone
typically being between the star-point current transformer
and the phase transformers of the star-wound winding.
 
Is This Answer Correct ?    11 Yes 2 No
Raghavendran
 
 
 
Answer
# 3
Restricted earth fault function only protect the specified
zone .But sensitive earth fault function can protect all
earth faults(only applicaple for after start of ct point).
both protection analog inputs taking from neutral ct of
power transformer.but in ref taking ct reference for all
phases of ct for making protection of specified area .
setting of ref lesser then sef.sef also back up for ref.
both protection only applicable for star side for
transformer
 
Is This Answer Correct ?    2 Yes 1 No
Surendar
 

 
 
 
Other Electrical Engineering Interview Questions
 
  Question Asked @ Answers
 
how capacitor control the power factor/ ABB 2
why normally Generator rating are between 11Kv to 22Kv? Torrent-Power 7
Difference Between B Curve & C Curve in MCB.   2
how can we know the size of cable cross-section from current rating ?   3
what are the application of over current relay?   2
for testing busbar (33kv) hi-pot .whether we can apply DC r not.and what is the test volt for that .explain   4
photo conductive cell Bhel 3
Can the Neutral and Body Earthpits of a transformer conncted together by Earth strips under ground.   4
what is the surge arrestor?how it operates?what is the range for it?   4
if we convert ampers into kw,which one formula use by us,pls tell me? ABB 11
what is the voltage between nutral and earth?   2
usually why bettery voltage are 1.5V, even if you open a 9V battery there are six 1.5V batteries in series. is it not possible to increase this voltage other than putting in series   1
 
For more Electrical Engineering Interview Questions Click Here 
 
 
 
 
 


   
Copyright Policy  |  Terms of Service  |  Articles  |  Site Map  |  RSS Site Map  |  Contact Us
   
Copyright 2013  ALLInterview.com.  All Rights Reserved.

ALLInterview.com   ::  KalAajKal.com