4.33
Date Code 20170814
Instruction Manual
SEL-700G Relay
Protection and Logic Functions
Group Settings (SET Command)
Figure 4.16
87N Element Logic Diagram
Set E87N := Y to enable the ground differential elements.
Set the 87N1P element sensitively, considerably lower than 50 percent of the
maximum ground differential current and disregarding the system
contribution (Idiff), to detect the highest number of faults. With this high
sensitivity, there is some risk of element pickup resulting from phase current
transformer saturation during external three-phase faults close to the
generator. To help ensure that this pickup does not cause a misoperation, set
the 87N1D time delay longer than the longest clearing time for a severe,
external fault.
Idiff = Ignd / CTRN
Set the 87N2P element less sensitively to detect severe ground faults high in
the generator windings or on the generator bushings. When the protected
generator is connected to a bus that can source ground fault current, set 87N2P
87N1
87N2P
87N1P
87N2T
87N2
87N1T
IG
I87N
IGY
IN
IGX
87NTC
Relay
Word
Bits
SEL
OGIC
Setting
87N1D
0
sec
87N2D
0
sec
| (IN - IG) |
1
2
S1
–1
Notes:
SEL-700G0/GT+: S1 set to Pos. 1.
SEL-700G1: S1 set as follows:
Pos . 1 - if X_CUR_IN := TERM
Pos. 2 - if X_CUR_IN := NEUT
CTRX
CTRN
CTRY
CTRN
Table 4.4
Ground Differential Settings
Setting Prompt
Setting Range
Setting Name :=
Factory Default
GND DIFF EN
Y, N
E87N := N
LVL1 GND DIFF PU
(0.10 • CTR/CTRN - 15.00) A
a
a
Ranges and/or default settings shown are for relay models with 5 A rated neutral current
input. Divide by 5 for the 1 A rated input. CTR = ratio of phase CTs located at generator
terminals.
87N1P := 2.5 A
LVL1 GND DIFF DLY
0.00-400.00 s
87N1D := 0.10
LVL2 GND DIFF PU
OFF, (0.10 • CTR/CTRN - 15.00) A
a
87N2P := OFF
LVL2 GND DIFF DLY
0.00-400.00 s
87N2D := 0.00
87N TRQCTRL
SEL
OGIC
87NTC := 1
where
Ignd = Maximum generator contribution to ground faults
CTRN = Neutral CT ratio setting
Summary of Contents for SEL-700G Series
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