GE Multilin g60

5-246 G60 Generator Protection System GE Multilin
5.7 CONTROL ELEMENTS 5 SETTINGS
5
The reset time of the thermal overload protection element is also time delayed using following formula:
(EQ 5.50)
In the above equation,
• τ
rst
= thermal protection trip time constant.
• T
min
is a minimum reset time setting
Figure 5–138: 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 5.51)
When current is less than the dropout level, I
n
> 0.97 × k × I
B
, the element starts decreasing the thermal energy:
t
rst

rst
kI
B

2
I
2
kI
B

2
–
---------------------------- -



ln T
min
+=
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E
n
E
n 1–
t
t
op In
---------------+=