5-298 D30 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
CONTROL ELEMENTS CHAPTER 5: SETTINGS
5
The reset time of the thermal overload protection element is also time delayed using following formula:
Eq. 5-27
where
Ï„
rst
= thermal protection trip time constant
T
min
= a minimum reset time setting
Figure 5-172: 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. 5-28
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