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8-26
Breaker Monitor and Metering Functions
Date Code 20011205
SEL-311B Instruction Manual
Demand Current Logic Output Application—Raise Pickup for Unbalance Current
During times of high loading, the residual ground overcurrent elements can see relatively high
unbalance current I
G
(I
G
= 3I
0
). To avoid tripping on unbalance current I
G
, use Relay Word bit
GDEM to detect the residual ground (unbalance) demand current I
G(DEM)
and effectively raise the
pickup of the residual ground time-overcurrent element 51GT. This is accomplished with the
following settings from Table 8.3, pertinent residual ground overcurrent element settings, and
SEL
OGIC
control equation torque control setting 51GTC:
EDEM
=
THM
DMTC
=
5
GDEMP
=
1.0
51GP =
1.50
50G2P
=
2.30
51GTC = !GDEM + GDEM * 50G2
Refer to Figure 8.13, Figure 8.14, and Figure 3.19.
Figure 8.14: Raise Pickup of Residual Ground Time-Overcurrent Element for Unbalance
Current
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