ABB Relion Technical Manual page 346

Section 11
Secondary system supervision
340
of MCBOP signal to prevent the unwanted operation of voltage dependent function due
to non simultaneous closing of the main contacts of the miniature circuit breaker.
The input signal 89b is supposed to be connected via a terminal binary input to the N.C.
auxiliary contact of the line disconnector. The 89b signal sets the output signal BLKV in
order to block the voltage related functions when the line disconnector is open. The
impedance protection function does not have to be affected since there will be no line
currents that can cause malfunction of the distance protection.
1MRK 502 048-UUS A
Technical manual