Transformer Short circuit calculation at Secondary terminals

• In a simplified approach, the impedance of the MV system is assumed to be negligibly small, so that:

${\displaystyle Isc={\frac {In\times 100}{Usc}}}$

where

${\displaystyle In={\frac {S\times 10^{3}}{U_{20}{\sqrt {3}}}}}$

and:

S = kVA rating of the transformer
U20 = phase-to-phase secondary no-load voltage
In = rated current of the transformer
Isc = short-circuit current in amps
Usc = short-circuit impedance voltage of the transformer in %.

KARMA

Minimum Excavation depth for HT & LT cables

Minimum IR values of HT & LT INSTALLATIONS

As per IE Rules-1956

HT INSTALLATIONS 

• At a pressure of 1000 V applied between each live conductor and earth for a period of one minute the insulation resistance of HV installations shall be at least 1 Mega ohm or as specified by the Bureau of Indian Standards.

• Medium and Low Voltage Installations- At a pressure of 500 V applied between each live conductor and earth for a period of one minute, the insulation resistance of medium and low voltage installations shall be at least 1 Mega ohm or as specified by the Bureau of Indian Standards] from time to time.

Minimum IR value for HT cables

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