4.41
Date Code 20150130 Instruction Manual SEL-787 Relay
Protection and Logic Functions
Basic Protection
The negative-sequence time-overcurrent element 51QnT responds to the 3I2
current as shown in Figure 4.23.
Figure 4.23 Negative-Sequence Time-Overcurrent Element 51Q1T and
51Q2T
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 below three cycles.
Table 4.13 Winding n Negative-Sequence Time-Overcurrent Settings (n = 1, 2)
Setting Prompt Setting Range
Setting Name :=
Fac tory Default
NSEQ TOC LEVEL OFF, 0.50–16.00 A
a
,
0.10–3.20 A
b
a
For I
NOM
=5 A.
b
For I
NOM
=1 A.
51QnP :=OFF
51QnP := OFF
NSEQ TOC CURVE U1, U2, U3, U4, U5, C1, C2,
C3, C4, C5
51QnC := U3
NSEQ TOC TDIAL 0.50–15.00
c
,
0.05–1.00
d
c
For 51_C := U_.
d
For 51_C := C_.
51QnTD := 3.00
EM RESET DELAY Y, N 51QnRS := N
CONST TIME ADDER 0.00–1.00 sec 51QnCT := 0.00
MIN RESPONSE TIM 0.00–1.00 sec 51QnMR := 0.00
NSEQ TOC TRQCTRL SEL
OGIC 51QnTC := 1
Table 4.14 Neutral Overcurrent Settings (Sheet 1 of 2)
Setting Prompt Setting Range
Setting Name :=
Fac tory Default
NEUT IOC LEVEL OFF, 0.50–96.00 A
a
0.10–19.20 A
b
50N11P := OFF
NEUT IOC DELAY 0.00–5.00 sec 50N11D := 0.50
NEUT IOC TRQCTRL SEL
OGIC 50N11TC := 1
NEUT IOC LEVEL OFF, 0.50–96.00 A
0.10–19.20 A
b
50N12P := OFF
51QnTC
SEL
OGIC
Torque Control
SELOGIC
Setting
(From Figure 4.14)
51QnP
|3I
2
Wn|
Setting
Torque Control Switch
Pickup
Curve
Timeout
Reset
51QnP
51QnR
51QnT
51QnTC Torque Control
State Switch Position
Logical 1 Closed
Logical 0 Open
Setting
51QnRS = Reset Timing
Y Electromechanical
N 1 Cycle
Relay
Word
Bits
51QnT Negative-Sequence
Time-Overcurrent Element
Curve Timing and Reset Timing
51QnP Pickup
51QnC Curve Type
51QnTD Time Dial
51QnRS Electromechanical
Reset? (Y/N)
51QnCT Const. Time Add.
51QnMR Min. Response
Settings
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