ABB Relion 670 Series Technical Reference Manual page 292

Section 6
Impedance protection
286
Or
A fault inception is detected
If it is later detected that it was an internal fault that made the function issue the
BLKCHST signal, the function will issue a CHSTOP signal to unblock the remote end.
The criteria that have to be fulfilled for this are:
1. The function has to be in pilot mode, that is, the setting has to be set to Enabled
2. The carrier send signal should be blocked, that is, input signal BLOCKCS is On and,
3. A reverse fault should not have been detected while the carrier send signal was not
blocked, that is, input signals REVSTART and BLOCKCS is not activated.
ZSMGAPC function has a built in loss of voltage detection based on the evaluation of
the change in phase voltage or the change in zero sequence voltage (3V0). It operates if
the change in phase voltages exceeds the setting or 3V0 exceeds the setting Delta3V0.
If loss of voltage is detected, but not a fault inception, the distance protection function
will be blocked. This is also the case if a fuse failure is detected by the external fuse
failure function and activate the input FUSEFAIL. Those blocks are generated by
activating the output BLKZ, which shall be connected to the input BLKZ on the
distance Mho function block.
During fault inception a lot of transients will be developed which in turn might cause
the distance function to overreach. The Mho supervision logic (ZSMGAPC) will
increase the filtering during the most transient period of the fault. This is done by
activating the output BLKZMD, which shall be connected to the input BLKZMTD on
mho distance function block.
High SIR detection
High SIR values increases the likelihood that CVT will introduce a prolonged and
distorted transient, increasing the risk for overreach of the distance function.
The SIR function calculates the SIR value as the source impedance divided by the
setting Zreach and activates the output signal HSIR if the calculated value for any of
the six basic shunt faults exceed the setting . The HSIR signal is intended to block the
delta based mho impedance function.
1MRK505222-UUS C
Technical reference manual