ABB Relion REG670, Technical Manual

Page: 160 / 1298

currents in this section can be tolerances of the current transformers used on both sides
of the protected generator. Slope in section 1 is always zero percent. Normally, with
the protected machine at rated load, the restrain, bias current will be around 1 p.u., that
is, equal to the machine rated current.
In section 2, a certain minor slope is introduced which is supposed to cope with false
differential currents proportional to higher than normal currents through the current
transformers.
The more pronounced slope in section 3 is designed to result in a higher tolerance to
substantial current transformer saturation at high through-fault currents, which can be
expected in this section.
Temporarily decreased sensitivity of differential protection is activated if the binary
input DESENSIT is (temporarily) set to 1 (TRUE). In this case, a new, separate limit
is superposed to the otherwise unchanged operate-bias characteristic. This limit is
called
TempIdMin and it is available as a setting. The value of the setting TempIdMin
must be given as a multiple of the setting IdMin . In this case no trip command can be
issued if all fundamental frequency differential currents are below the value of the
setting
TempIdMin .
AddTripDelay : If the input DESENSIT is activated also the operation time of the
protection function can be increased by using the setting AddTripDelay .
Section 6
1MRK502052-UEN B
Differential protection
154
Technical manual