The power transformer secondary 6.6kV neutral shall be
medium resistance earthed in order to limit the 6.6kV
system earth faults to low values such as to limit
excessive damage to 6.6kV equipments.
Also that the earth faults are not too low value to cause
earth fault relay non-operation.
System voltage = 6.6kV
System voltage per phase = 6.6/√3
Vph = 3810.6Volts
Earth fault current (I) =50A for 5 sec
NGR calculation is done on the basis of following formula,
In 110V DC supply,if a closed circuit gets open, How can we
identify the voltage which is measured after the
resistor(4KOhm) which is open with negative.it shows 55V +ve
when measured, also the actual positive source is 55V +ve
.Because there is no voltage drop in open circuit. How can
we identify whether this is the voltage which is series with
the resistor or the DC source direct +ve.