GE L90 Instruction Manual page 537

CHAPTER 5: SETTINGS
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:
When current is less than the dropout level, I
where
∆t is the power cycle duration
n is the power cycle index
t is the trip time calculated at index n as per the IEC255-8 cold curve or hot curve equations
op(In)
t is the reset time calculated at index n as per the reset time equation
rst(In)
L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
Figure 5-201: IEC 255-8 sample operate and reset curves
> 0.97 × k × I , the element starts decreasing the thermal energy:
n B
CONTROL ELEMENTS
> k × I , element starts increasing the
n B
5
Eq. 5-47
Eq. 5-48
5-351