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Fault Current Mostly Exist at Positive Value

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anggapra

Electrical
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Jun 28, 2018
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Hi All,

Recently there was single line to ground fault in my plant,

Below is the fault current recorded by the relay:

fault_PABL-ZELP_mhqrvx.jpg


Can someone explain why the fault current mostly exist at positive value? Is this because of the DC component? but the fault current didn't seem to be decaying.

Thanks in advance.

Angga
 
I think you are correct. Phase A ground fault current seems to be having a very large
DC componenet. That is why it hardly passes the zero axis.
Reason should be very high X/R ratio.
Is the measurement correct?
Was it happened near a generator?
 
The lower the R in the fault path, the longer the decay period.

Bill
--------------------
"Why not the best?"
Jimmy Carter
 
Is it a fault or was it simply that an A-phase transformer was energized?

I’ll see your silver lining and raise you two black clouds. - Protection Operations
 
Not that I know what this is, but this could be a ground fault on phase A.

Years ago I was a utility rep. for a customer project at a plant (I don't need to discuss which one).
The plant was adding a new fault reduction scheme that inserted a diode and resister in parallel, between the transformer X0 bushing and ground.
So I can't help but wonder, but it's not likely.
 
thanks all for your responds, additional information:
[ul]
[li]the breaker fed 34.5 kV subsea cable[/li]
[li]the cable was unloaded, the end breaker was open[/li]
[li]the cable is confirmed faulty, near cable end[/li]
[li]cable length is 108600 ft [/li]
[li]the CT's are 800/5 C100 [/li]
[/ul]
answering the questions:

Kiribanda said:
I think you are correct. Phase A ground fault current seems to be having a very large
DC componenet. That is why it hardly passes the zero axis.
Reason should be very high X/R ratio.
Is the measurement correct?
Was it happened near a generator?

I'm not sure the measurement is correct, but the main protection work properly (87L). It happened quite far from generator 333600 ft (electrically) from generator bus .

davidbeach said:
Is it a fault or was it simply that an A-phase transformer was energized?
confirmed single phase to ground fault on the cable.

How to calculate the X/R of system?
 
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