Follow Our FB Page << >> for Daily Laughter. We Post Funny, Viral, Comedy Videos, Memes, Vines...

Dear All,
In a 400V power system, ratio of three current transformers
installed incoming switchgear is 4000/1. Maximum three
phases short circuit current of this system is 48kA. One CT
is installed on neutral of upstream transformer (6/0.42kV,
solidly earthed) for 51G protection. Would you please inform
me about the correct CT ratio of this current transformer
(on neutral)??

Thanks a million

Answers were Sorted based on User's Feedback

Dear All, In a 400V power system, ratio of three current transformers installed incoming switchgea..

Answer / k.prakashchandra

The maximum earth fault current occurs when the phase comes
in contact with the earthed metal part.That will be about
230/0.5 i.e. about 500 A ,ignoring impedance of tr and
taking ER as 0.5 ohms.It is the usual practice to set EFR at
20% of OCR setting.For REFR the CT ratio should be the same
as that of phases.You can have a 2 core 4000:1 NCT and set
the 51G at 0.1 to 0.2 In ,using one of the two secondaries.

Is This Answer Correct ?    0 Yes 0 No

Dear All, In a 400V power system, ratio of three current transformers installed incoming switchgea..

Answer / k.prakashchandra

Further you can not expect much earth fault current in
neutral earthing as the voltage is only 230.Unless the phase
comes in contact with earthed metal part or welding is done
on the ground, this current will be too low to be picked up
by ct.As the power supply points are provided with fuses
,the relay may not get a chance to act at all.

Is This Answer Correct ?    0 Yes 0 No

Post New Answer

More Electrical Engineering Interview Questions

how to calculate regulation constants for over head lines? and what are the regulation constant for raccoon conductor at different voltage level and different P.F?

0 Answers  

How much earthing frequency is capable?

0 Answers  

TNC switch is also available in 1NO+1NC. What does it mean ?

1 Answers  

IN Electric train which type of motor is used,for what reason they uses?

3 Answers   L&T,

how to determine size of finolex power cables.

0 Answers   Finolex,

Given a collection of points P in the plane, a 1-set is a point in P that can be separated from the rest by a line; i.e. the point lies on one side of the line while the others lie on the other side. The number of 1-sets of P is denoted by n1(P). The maximum value of n1(P) over all configurations P of 19 points in the plane is 18

0 Answers   TCS,

which on of the transformer have more core losses and why? 1. Distribution Transformer 2. Power Transformer

5 Answers  

what happen when dc supply is given to the transformer

9 Answers   Bhel,

what is the working principle of ceiling fan and table fan?

10 Answers   ABC, Tata Steel Limited,

My requirement is 1VA,50/5A Current Transformer for Metering .If I select 15VA , 50/5A CT.Is there any possibility of Technical Problem ?

6 Answers  

refrigeration cycle?

1 Answers   MAHINDRA, Shapoorji Pallonji Group(SPCL),

what is the difference between Power and Distribution transformers ?

0 Answers  

  • Civil Engineering Interview Questions Civil Engineering (5075)
  • Mechanical Engineering Interview Questions Mechanical Engineering (4444)
  • Electrical Engineering Interview Questions Electrical Engineering (16598)
  • Electronics Communications Interview Questions Electronics Communications (3915)
  • Chemical Engineering Interview Questions Chemical Engineering (1092)
  • Aeronautical Engineering Interview Questions Aeronautical Engineering (214)
  • Bio Engineering Interview Questions Bio Engineering (96)
  • Metallurgy Interview Questions Metallurgy (361)
  • Industrial Engineering Interview Questions Industrial Engineering (258)
  • Instrumentation Interview Questions Instrumentation (2987)
  • Automobile Engineering Interview Questions Automobile Engineering (332)
  • Mechatronics Engineering Interview Questions Mechatronics Engineering (97)
  • Marine Engineering Interview Questions Marine Engineering (123)
  • Power Plant Engineering Interview Questions Power Plant Engineering (170)
  • Textile Engineering Interview Questions Textile Engineering (575)
  • Production Engineering Interview Questions Production Engineering (0)
  • Satellite Systems Engineering Interview Questions Satellite Systems Engineering (106)
  • Engineering AllOther Interview Questions Engineering AllOther (1377)