During VT secondary injection we faced simple and small problem.
A 10 X 2.5 Sq.mm cable is used between GIS "R" phase VT junction box to Local Control Cubical .
The VT is two winding VT and Secondary voltages as below
1a1- n = 64 v
1a2 - n = 64 v
2a1- n = 64 v
2a2 - n = 64 v
So in 10 X 2.5 Sq.mm cable 5 cores are used and all others are spare.
Now 64 V AC injected between terminal 1a1-n at VT junction box and measured at LCC and value is ok.
For cross checks we measured 2a2-n also and found same 60V voltage.
Witness says may be cable is damaged and cable is checked thoroughly and meggerd and every think is normal.
Some times if secondary cables connected with VT the applied voltage in secondary first winding will reflect in primary and it will induced voltage in second winding (Back Energization).
But we removed all secondary wires from VT.
After long discussion the problem is found it is due to Mutual induction.
Instant of AC voltage DC voltage is applied and there is no voltage in 2a1-n.
A 10 X 2.5 Sq.mm cable is used between GIS "R" phase VT junction box to Local Control Cubical .
The VT is two winding VT and Secondary voltages as below
1a1- n = 64 v
1a2 - n = 64 v
2a1- n = 64 v
2a2 - n = 64 v
So in 10 X 2.5 Sq.mm cable 5 cores are used and all others are spare.
Now 64 V AC injected between terminal 1a1-n at VT junction box and measured at LCC and value is ok.
For cross checks we measured 2a2-n also and found same 60V voltage.
Witness says may be cable is damaged and cable is checked thoroughly and meggerd and every think is normal.
Some times if secondary cables connected with VT the applied voltage in secondary first winding will reflect in primary and it will induced voltage in second winding (Back Energization).
But we removed all secondary wires from VT.
After long discussion the problem is found it is due to Mutual induction.
Instant of AC voltage DC voltage is applied and there is no voltage in 2a1-n.
