Negative Sequence Filter

[Valtrex]

Hi
Could anyone refer me to a book or some other resource where I would find how elementry sequence filters can be used to measure negative sequence voltages and current. Thanks

 

[busbar]

See thread238-34288 for discussion.

 

[Valtrex]

Thanks BusBar
but do you know if I could get an online version of the book Westinghouse "Applied Protective Relaying,?

 

[dpc]

I think this book is still in print and published by ABB in the U.S. You may want to check with ABB. I do not believe it is available on-line.

 

[Valtrex]

Thanks I got a hold of a copy of the book. However, in chapter 3 of the 1982 edition, where they spoke about sequence voltage networks, they stated that Z + R is designed so that the I lags V by 60 deg. Why is this done and how does it lead to the filtering of the negative sequence voltage?

 

[electricpete]

The definition of negative sequence as computed vectorially is something like
I- = Ia + alpha Ib + alpha^2 Ic where alpha is exp(j*120degrees). Or you may have to switch the coefficients of Ib and Ic. Please look it up and double check me.

So if you start with Ia, Ib, Ic, and want to compute directly from the definition, you need to figure out ways to come up with 120 degree phase shifts. One way is a 60 degree phase shift combined with reversal (180-60-120).

I'm suspect there are a variety of other ways to tackle it than to apply the definition directly.