Sel SEL-787 - Figure 4.19 Instantaneous Overcurrent Element Logic

4.36
SEL-787 Relay Instruction Manual Date Code 20150130
Protection and Logic Functions
Basic Protection
Figure 4.19 Instantaneous Overcurrent Element Logic
When the harmonic distortion index exceeds the fixed threshold, which
indicates severe CT saturation, the phase overcurrent elements operate on the
output of the peak detector. When the harmonic distortion index is below the
fixed threshold, the phase overcurrent elements operate on the output of the
cosine filter.
50Pn1P
|IAWn|
IAWn
IBWn
ICWn
IN1
PHROT
IGWn
|IPWn|
|IN1|
|IGWn|
50Pn1AP
Current
Magnitude
Calculations
50Pn1BP
|ICWn|
50Pn1CP
50Pn1TC
50PnxP
50PnxT
50N1yP
50N1yT
Settings
(Maximum Phase Current Magnitude)
(Neutral Current Magnitude)
(Residual Current Magnitude)
50N1yD
0
50PnxD
0
Negative-Sequence
Current Calculation
(Negative-Sequence Current Magnitude)
|3I2Wn|
50GnyP
50GnyT
50QnyP
50QnyT
50QnyD
0
50GnyD
0
|IAWn|
|IBWn|
(Phase A Current Magnitude)
(Phase B Current Magnitude)
(Phase C Current Magnitude)
|ICWn|
50Pn1CT
|IBWn|
50QnyP
50GnyP
50N1yP
50PnxP
|3I2Wn|
50QnyTC
|IGWn|
50GnyTC
|IN1|
50N1yTC
|IPWn|
50PnxTC
Relay
Word
Bits
50Pn1BT
50Pn1AT
50Pn1P
50Pn1P
50Pn1D
0
50Pn1D
0
50Pn1D
0
Torque Control switch position = Closed when corresponding control bit is asserted (e.g., 50P11TC = 1),
Open when it is deasserted.
Relay Word bit ORED50T (not shown) asserts when any of the 50_T bit asserts.
x = 1, 2, 3, or 4
y = 1 or 2
n = 1 or 2 (Winding)