GE B30 UR Series

GE Multilin B30 Bus Differential System 5-175
5 SETTINGS 5.7 CONTROL ELEMENTS
5
To ensure element accuracy for high overcurrent conditions, the maximum value of I/(k x I
B
) is limited to 8, even when real-
istically it is exceeding this value.
The reset time of the thermal overload protection element is also time delayed using following formula:
(EQ 5.16)
In the above equation,
• τ
rst
= thermal protection trip time constant.
• T
min
is a minimum reset time setting
Figure 5–78: IEC 255-8 SAMPLE OPERATE AND RESET CURVES
The thermal overload protection element estimates accumulated thermal energy E using the following equations calculated
each power cycle. When current is greater than the pickup level, I
n
> k × I
B
, element starts increasing the thermal energy:
(EQ 5.17)
t
rst
τ
rst
kI
B
()
2
I
2
kI
B
()
2
–
-----------------------------



ln× T
min
+=
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E
n
E
n 1–
tΔ
t
op In()
---------------
+=