JUMPER OPENING IN HV SIDE OF TRANSFORMER
JUMPER OPENING IN HV SIDE OF TRANSFORMER
(OP)
Sir,
Consider a 66/11kv transformer (star-star earthed at both side neutrals) in a solidly earthed system. Also consider one 11/0.44kv Delta/star transformer is connected to 11kv side of the 66/11kv transformer. The supply is fed from 66kv side of the 66/11kv transformer and this is stepped down to 440volts by 11/0.44kv transformer for ditribution. The 66/11kv transformer is of core type.
Suppose 'A' phase on 66kv side of the transformer became disconnected by jumper opening of the 'A' phase of the line connected to the transformer. In this situation, I think the flux due to 'B' and 'C' phase currents will flow through limb of the 'A' phase of transformer core. But in the 66kv side, there will be only two phases and the 'A' phase in the 11kv side will carry current due to the flux in 'A' phase core due to the currents in 'B' and 'C' phases in the 66kv. That is, in 11kv side there will be 3 phase currents. But the current in 66kv will increase in order to supply current in 'A' phase in 11kv side. If earth fault relay was connected in 66kv side cts, it will trip if the residual current is above pick up value due to the load in 11kv side.
Am I correct? I want to know whether my analysis is correct. Please help me with your valuable comments.
with regards,
appunni
Consider a 66/11kv transformer (star-star earthed at both side neutrals) in a solidly earthed system. Also consider one 11/0.44kv Delta/star transformer is connected to 11kv side of the 66/11kv transformer. The supply is fed from 66kv side of the 66/11kv transformer and this is stepped down to 440volts by 11/0.44kv transformer for ditribution. The 66/11kv transformer is of core type.
Suppose 'A' phase on 66kv side of the transformer became disconnected by jumper opening of the 'A' phase of the line connected to the transformer. In this situation, I think the flux due to 'B' and 'C' phase currents will flow through limb of the 'A' phase of transformer core. But in the 66kv side, there will be only two phases and the 'A' phase in the 11kv side will carry current due to the flux in 'A' phase core due to the currents in 'B' and 'C' phases in the 66kv. That is, in 11kv side there will be 3 phase currents. But the current in 66kv will increase in order to supply current in 'A' phase in 11kv side. If earth fault relay was connected in 66kv side cts, it will trip if the residual current is above pick up value due to the load in 11kv side.
Am I correct? I want to know whether my analysis is correct. Please help me with your valuable comments.
with regards,
appunni






RE: JUMPER OPENING IN HV SIDE OF TRANSFORMER
If you did have zero-seq current in the 11 kV, and the 66-11 kV transformer were of 3-legged core design, there would be no path for the zero-seq flux in the core. It would flow in the air and tank (possibly causing tank heating).
RE: JUMPER OPENING IN HV SIDE OF TRANSFORMER
Consider a 66/11kv transformer (star-star earthed at both side neutrals) in a solidly earthed system.
///This connection propagates the zero sequence current, if it exists, i.e. if the load is unbalanced.\\\
Also consider one 11/0.44kv Delta/star transformer is connected to 11kv side of the 66/11kv transformer.
///This connection does not propagate the zero sequence current whether the secondary load is balanced or unbalanced.\\\
The supply is fed from 66kv side of the 66/11kv transformer and this is stepped down to 440volts by 11/0.44kv transformer for ditribution. The 66/11kv transformer is of core type.
Suppose 'A' phase on 66kv side of the transformer became disconnected by jumper opening of the 'A' phase of the line connected to the transformer. In this situation, I think the flux due to 'B' and 'C' phase currents will flow through limb of the 'A' phase of transformer core. But in the 66kv side, there will be only two phases and the 'A' phase in the 11kv side will carry current due to the flux in 'A' phase core due to the currents in 'B' and 'C' phases in the 66kv.
///The upstream power supply will see this situation as an unbalanced three phase load. The zero sequence current can materialize if the upstream power supply connection permits it, i.e. grounded y-connection of transformer or generator exists.\\\
That is, in 11kv side there will be 3 phase currents.
///If y-connection loses one line, ther will only be one phase voltage and current available downstream.\\\
But the current in 66kv will increase in order to supply current in 'A' phase in 11kv side. If earth fault relay was connected in 66kv side cts, it will trip if the residual current is above pick up value due to the load in 11kv side.
///Yes. If will be clear, if you draw a diagram of this situation and formulate mathematical relationships.\\\
RE: JUMPER OPENING IN HV SIDE OF TRANSFORMER
With regards,
appunni
RE: JUMPER OPENING IN HV SIDE OF TRANSFORMER
If the open phase touches the ground, sparks will fly because the 11-0.44 kV delta windings connected to the open phase will act as a voltage divider between the intact phases. Voltage on the open phase will be 1/2 the normal voltage.
__________ A 6.35 kV <0° |
| C |
| C |
| C_______ B open 3.175 kV <30° | 11 kV <150°
| C |
| C |
| C_______ C 6.35 kV <120° V
| C
| C
| C
|__|
RE: JUMPER OPENING IN HV SIDE OF TRANSFORMER
with regards,
appunni
RE: JUMPER OPENING IN HV SIDE OF TRANSFORMER