high impedance fault detection

[magoo2]

What is the status of providing additional protection for high impedance faults? Is it widely used?

I have seen papers on it over the years and just wondered if anyone is using it. Schweitzer has a relay based on harmonic signatures. Sounds like what Don Russell developed many years ago.

We occasionally drop an overhead conductor on sand and get no fault current. It's a safety concern, but is the additional protection worth it? We don't think so, but I'm curious if any utilities out there use high impedance relaying.

 

[bacon4life]

We have installed a few relays with Hi-Z protection but I don't think any of those feeders have experienced a high impedance feeder fault since then. One of the relays did alarm for a loose secondary connection.

 

[DTR2011]

From what I've heard, the reason that more utilities have not adopted this is more of a legal issue. As it was explained to me from a former HP&L Protection Engr, due to the fact that there is a known solution to downed conductors, nearly all lines would have to have them installed, vs. not adopting the technology and having the problem "our of our control", or something to that effect.

Basically it was a way for utilities to shield themselves from the expense of having to upgrade all of their OH Lines that are susceptible to a downed conductor, verses the liability of not having all of the lines protected and someone is harmed. I was told this several years ago, so this is only the essence of what I remember.

I suppose this would make sense as both GE and SEL have this ability and I've yet to see it used.

I would be interested in what others have to say as well.