Answer / amit khamesra

NGR and NGT serves the same purpose of limting the earth
fault current to the rated values which basically depends
upon the core damage curve of generator. Differece is NGT
gives earth fault protection of 100 % winding whereas NGR
protects only 95% of the generator winding. Potential
difference of the 5% winding (towards neutral) with respect
to neutral is very less so the earth fault in that region
of the winding is not sensed. This is avoided in NGT using
sensing of 3rd harmonic under voltage based principle in
secondary of the NGT.

Answer / devang machchhar

with the same value of resistance, NGT shows more
resistnace in ground circuit and limit the current for
instantanious high fualts at the first 3 power cycles,
providing safety to the generator or transformer.

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