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3 Phase Trip 2
- Thread starter rogerj1
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- #4
oldfieldguy
Electrical
rbulsara and stevenal both have good scenarios.
I've been responsible for several records like stevenal describes.
It's an interesting exercise to run the oscillography data from a fault recorder through a vector generation program and watch the vectors swing around as a fault progresses.
old field guy
I've been responsible for several records like stevenal describes.
It's an interesting exercise to run the oscillography data from a fault recorder through a vector generation program and watch the vectors swing around as a fault progresses.
old field guy
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2
- #9
I just got done downloading a fault record that has all three phases identical in magnitude and phase. The fault was a single phase to ground fault on a substation 12.5 kV bus. The fault record was from an SEL-587 relay protecting a 480V-12.5kV generator step-up transformer. The 12.5kV side is connected grd-wye, the 480 volt side is connected delta. The 480 volt breaker was open.
The 12.5kV line current was pure zero-sequence. Primary current was 1072A and resulted in a 51P trip in 0.42 sec.
The substation bus was fed by a 100kV-12.5kV power transformer. A racoon was found below the bus and a bus insulator showed burn marks. The racoon did not survive the incident.
The 12.5kV line current was pure zero-sequence. Primary current was 1072A and resulted in a 51P trip in 0.42 sec.
The substation bus was fed by a 100kV-12.5kV power transformer. A racoon was found below the bus and a bus insulator showed burn marks. The racoon did not survive the incident.
- Thread starter
- #10
jghrist,
This is pretty much what happened in our case. We had a similar generation source open up on the delta side of the step-up TX. A ground fault on the secondary produced zero seq. current in the wye connection, thus all three phases same in magnitude and phase. We are putting together a trouble report study on this event and maybe I can share more details once that is complete. Thanks to everyone for their interest and input.
This is pretty much what happened in our case. We had a similar generation source open up on the delta side of the step-up TX. A ground fault on the secondary produced zero seq. current in the wye connection, thus all three phases same in magnitude and phase. We are putting together a trouble report study on this event and maybe I can share more details once that is complete. Thanks to everyone for their interest and input.
With the fault on the 12.5 kV bus, there are parallel paths in the sequence networks. One is through the power transformer to the transmission system source. The other path is through the step-up generator transformer to the generator.
In the zero-sequence network, there is an open circuit on the delta side of both paths; on the transmission system side of the power transformer impedance (the power transformer is delta-grd wye) and on the generator side of the generator transformer impedance.
There is a short to neutral on the wye side. This short to neutral on the generator transformer provides a path in the zero-sequence network. There is no path on the generator side of the positive- and negative-sequence networks because the generator side breaker is open.
The only path on the generator side is in the zero-sequence network, so only zero-sequence current flows through the generator transformer to the fault point. The total fault current includes all sequences, but not the portion flowing from the generator transformer.
Looking at it in a more physical manner, consider that with the generator side breaker open, there is no line current on the delta side of the generator transformer. The current in each delta winding must be the same because the the windings are in series with no other connections. The current "circulates" in the delta. The current in the high side wye windings are directly proportional to the current in the low side windings, so they are also all equal.
The line current from the generator transformer in the unfaulted phases goes through the 12.5 kV bus, through the power transformer windings to neutral and through the racoon to the faulted phase.![[mouse]](/data/assets/smilies/mouse.gif "[mouse] [mouse]")
In the zero-sequence network, there is an open circuit on the delta side of both paths; on the transmission system side of the power transformer impedance (the power transformer is delta-grd wye) and on the generator side of the generator transformer impedance.
There is a short to neutral on the wye side. This short to neutral on the generator transformer provides a path in the zero-sequence network. There is no path on the generator side of the positive- and negative-sequence networks because the generator side breaker is open.
The only path on the generator side is in the zero-sequence network, so only zero-sequence current flows through the generator transformer to the fault point. The total fault current includes all sequences, but not the portion flowing from the generator transformer.
Looking at it in a more physical manner, consider that with the generator side breaker open, there is no line current on the delta side of the generator transformer. The current in each delta winding must be the same because the the windings are in series with no other connections. The current "circulates" in the delta. The current in the high side wye windings are directly proportional to the current in the low side windings, so they are also all equal.
The line current from the generator transformer in the unfaulted phases goes through the 12.5 kV bus, through the power transformer windings to neutral and through the racoon to the faulted phase.
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