GUID-9AACAC66-BF72-430C-AAC7-2E52C3DC4487-ANSI V1 EN
Figure 256: Operation logic of instantaneous high stage
Reset of the blocking signals (de-block)
All three blocking signals, that is, waveform and second and fifth harmonic, have a
counter, which holds the blocking on for a certain time after the blocking conditions have
ceased to be fulfilled. The deblocking takes place when those counters have elapsed. This
is a normal case of deblocking.
The blocking signals can be reset immediately if a very high differential current is
measured or if the phase difference of the compared currents (the angle between the
compared currents) is close to zero after the automatic vector group matching has been
made (in a normal situation, the phase difference is 180 degrees). This does not, however,
reset the counters holding the blockings, so the blocking signals may return when these
conditions are not valid anymore.
External blocking functionality
87T has three inputs for blocking.
• When the BLOCK input is active ("TRUE"), the operation of the function is blocked
but measurement output signals are still updated.
• When the BLK_OPR_LS input is active ("TRUE"), 87T operates normally except
that the OPR_LS output is not active or activated in any circumstance. Additionally,
the TRIP output can be activated only by the instantaneous high stage (if not blocked
as well).
• When the BLK_OPR_HS input is active ("TRUE"), 87T operates normally except
that the OPR_HS output is not active or activated in any circumstance. Additionally,
the TRIP output can be activated only by the biased low stage (if not blocked as well).
4.3.2.5 Application
87T is a unit protection function serving as the main protection for transformers in case of
winding failure. The protective zone of a differential protection includes the transformer,
Section 4 1MAC059074-MB A
Protection functions
514 615 series ANSI
Technical Manual
To Next Page
Loading...
