2021-08-03 at 11:08 am
#1938
BEHNAM
This is the idea of GEC . Some reputable firms believe that in case of impedance grounding REF is not necessary . They say , suppose neutral point has been grounded through a resistance so that the CT ratio is 20/1 . On the other hand CT ratio of line CTs will be 2000/1. In this case for conforming of currents injected to relay you are forced to dilute the 1 Ampere in neutral CT secondary by 100 times (in fact the ratio of 2000/1 to be made inside relay) . In this case relay is very sensitive and unstable . Some designers advise summation (throat )CT or zero sequence CT in line side with ratio of 20/1 . Even with this solution some instabilities have been reported .