GE F35 Instruction Manual page 340

CONTROL ELEMENTS
The reset time of the thermal overload protection element is also time delayed using following formula:
where
τ = thermal protection trip time constant
rst
T = a minimum reset time setting
min
5
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
thermal energy:
5-214
 
kI
B
  ------------------------ -
t = ln 
rst rst
2


I
–
Figure 5-114: IEC 255-8 sample operate and reset curves
E = E + ------------- -
n n 1
– t
2
 
 + T
min
2


kI
B
> k × I , element starts increasing the
n B
t 
 
op In
F35 MULTIPLE FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 5: SETTINGS
Eq. 5-24
Eq. 5-25