Schweitzer Engineering Laboratories SEL-751 - Table 4.15 Neutral Time-Overcurrent Settings; Figure 4.7 Negative-Sequence Time-Overcurrent Element 51 QT

4.20
SEL-751 Relay Instruction Manual Date Code 20170927
Protection and Logic Functions
Group Settings (SET Command)
The negative-sequence time-overcurrent element 51QT responds to the 3I2
current as shown Figure 4.7.
q From Figure 4.2; w Figure 4.40.
Figure 4.7 Negative-Sequence Time-Overcurrent Element 51QT
False negative-sequence current can transiently appear when a circuit breaker
is closed and balanced load current suddenly appears. To avoid tripping for
this transient condition, do not use a time-dial setting that results in curve
times slower than three cycles.
Table 4.15 Neutral Time-Overcurrent Settings (Sheet 1 of 2)
Setting Prompt Setting Range
Setting Name :=
Fac to ry Defa ult
TOC TRIP LVL OFF, 0.25–24.00 A
a
0.05–4.80 A
b
10.00–960.00 mA
c
51N1P := OFF
TOC CURVE SEL U1, U2, U3, U4, U5,
C1, C2, C3, C4, C5
51N1C := U3
TOC TIME DIAL 0.50–15.00
d
0.01–1.50
e
51N1TD := 1.50
EM RESET DELAY Y, N 51N1RS := N
CONST TIME ADDER 0.00–1.00 sec 51N1CT := 0.00
MIN RESPONSE TIM 0.00–1.00 51N1MR := 0.00
TOC TRQ CONTROL SEL
OGIC 51N1TC := 1
TOC TRIP LVL OFF, 0.25–24.00 A
a
0.05–4.80 A
b
10.00–960.00 mA
c
51N2P := OFF
TOC CURVE SEL U1, U2, U3, U4, U5,
C1, C2, C3, C4, C5
51N2C := U3
TOC TIME DIAL 0.50–15.00
d
0.01–1.50
e
51N2TD := 1.50
EM RESET DELAY Y, N 51N2RS := N
CONST TIME ADDER 0.00–1.00 sec 51N2CT := 0.00
51QP
Setting
51QTC
Torque Control Switch
Torque
Control
Pickup
51QP
Reset
51QR
Curve
Timeout
51QT
Torque
Control Torque Control
State Switch Position
Logical 1 Closed
Logical 0 Open
Setting
51QRS= Reset Timing
Y Electromechanical
N 1 Cycle
Relay
Word
Bits
SEL OGIC
Setting
51QT Residual
Time-Overcurrent Element
Curve Timing and Reset Timing
Settings
51QP Pickup
51QC Curve Tpe
51QTD Time Dial
51QRS Electromechanical
Reset? (Y/N)
51QCT Const. Time Add.
51QMR Min. Response
|3I2|
1
Q1DIR
2