Schweitzer Engineering Laboratories SEL-787 - Page 91

4.13
Date Code 20081022 Instruction Manual SEL-787 Relay
Protection and Logic Functions
Basic Protection
shifts relative to Phase A, when ACB phase rotation is used instead of ABC.
In ACB phase rotation the three phases still rotate in a counterclockwise
direction, but C-phase is in the 120-degree lagging position and B-phase leads
by 120 degrees, relative to A-phase.
The discussions below assume ABC phase rotation, unless mentioned
otherwise.
The “0” setting value is intended to create no changes at all in the currents and
merely multiplies them by an identity matrix. Thus, for WnCTC = 0,
that is,
The “1” setting performs a 30-degree compensation in the counterclockwise
direction, as would a delta CT connection of type DAB (30-degree leading).
The name for this connection comes from the fact that the polarity end of the
A phase CT connects to the nonpolarity end of the B phase CT, and so on, in
forming the delta. Thus, for WnCTC = 1, the relay uses the following
[CTC(m)] matrix:
that is,
The ‘11” setting performs a 330-degree compensation (11 • 30) in the
counterclockwise direction, or a 30-degree compensation in the clockwise
direction, as would a delta CT connection of type DAC (30-degree lagging).
The name for this connection comes from the fact that the polarity end of the
A phase CT connects to the nonpolarity end of the C phase CT, and so on, in
forming the delta. Thus, for WnCTC = 11, the relay uses the following
[CTC(m)] matrix:
IAWnC=IAWn
IBWnC=IBWn
ICWnC=ICWn
CTC 0()[]
1 0 0
0 1 0
0 0 1
•
CTC 1()[]
1
3
-------
1 –1 0
0 1 –1
1 0 1–
•=
IAWnC
IAWn IBWn–()
3
------------------------------------------=
IBWnC
IBWn ICWn–()
3
------------------------------------------=
ICWnC
ICWn IAWn–()
3
------------------------------------------=
CTC 11()[]
1
3
-------
1 0 –1
–1 1 0
0 –1 1
•=