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how netral CT is selected (including its details
specification)
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Answer Posted / bikash chandra pal
Neutral CT is generally used on earth connector connecting
the earth or ground & the star point of a Generator or
Transformer.
Neutral CT is selected based on the value of designed the
earth fault current which is supposed to return to
transformer or generator star point from earth.
Process of selection:-
primary rating : Designed E/F current x 1.2
Secondery rating : normally selected as 1A(reason being,
the distance between the relay & NCT which is located on
transformer bushing is generally longer),However, if the
distance is lesser & approximately within 25M, 5A secondery
also may be selected.
Accuracy class: To be selected based on application,eg: for
Stand by earth fault protection(51G) it may be 5P10. For
restricted earth fault protection(64R), PS calss CT is
applicable Vk to be calculated,Imag to be chosen based on
relay mnf's reccommendation. For Neumerical CT,mnf's
guideline need to be adhered.
BIL: based system requirement & CT construction(eg. for
window type CT system BIL is not applicable, as by virtue
of it's construction it is LT CT as primary is full voltage
isolated.But for BAR & wound type epoxy cast CT system BIL
is applicable.
Trust the above is clear. feel free to ask for
clarification if any
| Is This Answer Correct ? | 31 Yes | 3 No |
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