Faut Location in Distance Relays

[khadisa]

Hi

We have a Distance Relay From ALSTOM, Type LFZP111. The Line is 132KV and about 300KM Long. There are transformers at various point along the line. We set 80% (70KM) of the first segment as Zone 1 and the entire length of the line as Zone 2. What distance do We set as the length of the line for the Fault Locator? We initially set the entire length but are getting funny locations whenever there is a trip.

 

[davidbeach]

Fault location works on the assumption of consistent impedance for the entire protected line. Your taps will throw off the calculation. You could do some calculations to see what the relay would calculate for fault location for various faults on the main circuit and on the taps. At that point you could have a secret decoder ring that would tell you that if the relay says the fault happened at point x, that you should look around point y on the main circuit or around point z on tap q.

 

[jghrist]

I agree with davidbeach if the transformers are sources of fault current. If not, I don't see how they would affect the impedance to a fault on the main line as seen by the relay.

 

[davidbeach]

jghrist, distance to fault is an impedance calculation and the load impedance on a tap could influence the calculation of the fault location. If you have a tap near the end of the line where the relay is located and a fault much of the distance to the other end (given as 300km) the load impedance will be in parallel with the line impedance from the tap to the fault making it appear that the fault is closer to the relay end of the line than it is. The OP didn't say how much error he (she?) is getting, but if one is used to getting very good locations from untapped lines, a few percent error in impedance could (on a fairly high impedance line) could make for significant distance errors on the fault locations.

 

[jghrist]

OK, but then your secret decoder ring would have to factor in the load at each tap at the time of the fault.

 

[davidbeach]

True.

 

[bacon4life]

DavidBeach could still be right about the secret decoder if the entire transmission line is not built with the same construction type. We recently rebuilt a portion of one of our lines, with the impedance per mile changing significantly.

TYPE R1 X1
300 CU 0.21469 0.80731
1272AAC 0.07740 0.64223

khadisa, what do you mean by "funny"?

 

[khadisa]

Actually with Zone 1 setting of 70KM it will show zone 1 trip at a location of 220KM and sometimes the fault location will be much more than the length of the entire line.

 

[jghrist]

Sounds like you need to get Areva involved in determining what is wrong. Is there any consistency in the error? Does the relay have data recording for post fault analysis?