USE OF NEUTRAL GROUNDING RESISTOR IN EHV SYSTEM

[TPEC]

thread238-146364

CAN I USE NGR FOR TRANSFORMERS RATED ABOVE 11 KV?? WHAT MEASURES I HAVE TO TAKE WHILE INSTALLING NGR FOR SUCH SYSTEM VOLTAGE??HOW IT WIIL AFFECT SYSTEM FAULT LEVEL AND LIGHTING ARRESTER RATING??

 

[krisys]

TPEC,

For any unusual requirements, you have to give the justification.
Please let us know, why on earth you got such requirement of using NGR above 11kV.

Exception to the above is 22 and 33 kV industrial systems.

If you have to size the NGR (NER) for 22 or 33kV system then go for the Low resistance grounded system, (earth fault current limited to say 50 to 1200A).

Before doing this, please challenge this requirement and if possible try to get rid of NER, unless this is an industrial distribution system.

 

[FPelec]

Generally speaking, there is a substantial difference between "EHV systems" (as in the topic title) and "above 11 kV" (as in the text).
However, RTE (the French TSO) sometimes adopts low impedance grounding of some EHV (400 kV) transformers and autotransformers, to reduce the 1-phase fault currents.
Use of high resistance (i.e. about 500 to 1100 Ohm) grounding is quite common in several medium voltage (20 kV) industrial networks in Italy, as well as in some small public medium voltage distribution networks at 15 or 20 kV.



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