Distance relay - impedance characteristic question

[nettub]

Dear all!

I have a question about the impedance characteristics in the distance relay used for transmission line protection. I understand that in the first quadrant we have a inductive load and in the fourth quadrant we have a capacitive load. I, however, do not understand what we measure in the second quadrant that I marked red. We would have a negative resistance. Can someone please help me with that?

https://dl.dropboxusercontent.com/u/3809800/impedance_characteristics.jpg

Thanks,
Pauls

 

[jim hardy]

see if this old GE appnote helps

first 3 pages of

http://www.gedigitalenergy.com/multilin/notes/artsci/art04.pdf

i'd say it's inductive, sign of R showing direction of power flow.

 

[nettub]

Thanks for your answer.

That's what I thought and I also saw the paper. That means, however, that the relay is bi-directional. For me that's contradicting since the diagonal shown in my picture marks the operating direction of the relay. So when you want to detect both directions you would need 2 relays anyways. That means the -R and +X area would be redundant.

 

[jim hardy]

i think they're saying the math works out to a function that'd be bidirectional

there's discussion later on about adding restraint coils

i'm not a relay guy, just have watched over the shoulders of some genuine ones.

i'd resort to a genuine industrial training manual for in-depth discussions of how it's done in the real world..
http://www.pdfslibfree.com/applied-protective-relaying-westinghouse.pdf
http://www.osinerg.gob.pe/newweb/uploads/GFE/eventos/EVENTO%207/TEXTO%207A.pdf

 

[subtech]

This should help you.
It gets right at the heart of your question in a relay technician/relay engineer sort of way.

http://www.gedigitalenergy.com/multilin/notes/artsci/index.htm

I would download the entire book, but in particular you will want chapters 3 & 4.
Post again if you need further help.

 

[jim hardy]

Since the torques are in proportion to RMS currents squared, it looks to me like the basic device would be bidirectional...