Ground distance - mutual inductance

[ChristopherWalken]

I have two parallel lines that have mutual inductance and this is making the impedance seen by my ground distance relay higher than it actually for a fault on the remote bus. I am wanting to expand my zone 2 to cover maybe 40% instead of 25% of the next shortest segment in order to make sure that a line end fault will trip on zone 2 if both lines are in service. I also have fault current coming in from the other lines that is affecting the apparent impedance of how far I am going into the next line. I am looking at several scenarios (wind gen. out,ect) and just eyeballing the zones so that they operate correctly when one or both lines are in service with or without wind generation. Is this usually how it is done?

 

[davidbeach]

Hopefully you have a detailed model, OneLiner, Cape, etc., that includes the mutuals and all the sources. Then you run multiple fault cases until you are convinced that you have it all covered. That's why Mason's classic work is titled "The Art and Science of..." rather than simply "The Science of..."

 

[collies99]

Christopher:
1. Are you suggesting that due to parallel line configurations that Zone 2 ground mho set at 120% of the asscociated impedance may not operated for a remote end fault ?

3. Does your lines haave a sky wire system on ground return through earth ?