Dear All, In a 400V power system, ratio of three current transformers installe

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

Question Posted / majd-s

2 Answers
4840 Views
I also Faced
E-Mail Answers

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

wchich motor we are using in mixer?

4 Answers

what is 3rd Harmonics? how it is generated in alternator

2 Answers Aditya Birla,

why the Parameters : Base Voltage & Maximum Voltage can't be equal in value in a VFD (Variable Frequency Drive) ? How much the base voltage would be lower than the maximum voltage ? If 400 V is the 3 phase output of a VFD ... then what should be the base voltage ? thanks a lot

1 Answers Yaskawa,

Why DC excitation is used for alternators? Why cant it be AC?

35 Answers ABB, Ace Info, Alstom, Shalivahana Power,

how to calculate optimum loading for transformer?

6 Answers

why one side of tubelight glows after switch off ?

1 Answers

What the capacitor Current formula?, For 1 KVAr how amps its required? for using the KVAr for boosting the PF Design Calculation.( Eg: for 30 KVAr required how many KW?)

17 Answers Alstom, Call Centre, EDC, HCL, Procon Engineers,

hi, is there a difference in choosing bus bar for DC or AC ,,if there can anyone help me about. thanks

1 Answers

how the B-H loop obtain under the static condition

0 Answers

What is the meaning of C1, C61, C91 cable

0 Answers

what is prniciple of three phase IM?

3 Answers

what is the difference between transformer,converter and transducer

0 Answers

For more Electrical Engineering Interview Questions Click Here