Schweitzer Engineering Laboratories SEL-351 - Demand Current Logic Output Application - Raise Pickup for Unbalance Current

8-26 Breaker Monitor, Metering, and Load Profile Functions Date Code 20001006
SEL-351 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
SELOGIC Control Equation torque control setting 51GTC:
EDEM = THM
DMTC = 5
GDEMP = 1.0
51GP = 1.50
50G5P = 2.30
51GTC = !GDEM + GDEM*50G5
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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