Pilot aided scheme: 1-Bit vs 2-Bit Vs 4-Bit 1

[sushilksk]

We are using single bit pilot aided scheme for distance relays (one carrier signal for any type of faullt).

One manufacturers is recommending 4-Bit pilot scheme (1st bit AG, 2nd Bit BG, 3rd Bit CG and 4th bit all remaining type of faults 2P/3P).

And in between there is 2-Bit scheme also (1st bit AG/BC/BCG, 2nd bit BG/AC/ACG, 1st & 2nd both bits CG/AB/ABG/3P)

Higher bit schemes will require additional protection coupler channels. Any body using more than one bit for pilot scheme may share experience.

 

[davidbeach]

Relay to relay channels seem to come with 8 bits.

We use the first for direct trip, the second is the POTT key, the third is Drive to Lockout. The fourth, and sometimes the fifth, are local breaker status; doesn't do anything for the tripping but sure helps in event analysis. We have only a single example of single pole tripping and for that we use the scheme of the larger entity at the remote end. If I was regularly doing single pole trip and reclose, I'd move the DTL and 52a bits down a couple and have the three phase keys as bits 2-4. Just one key bit from one end that aligns with the single key bit at the other and trip that phase. Any other combination, trip all three phases.