GE L90 Instruction Manual page 412

5.7 CONTROL ELEMENTS
The reset time of the thermal overload protection element is also time delayed using following formula:
In the above equation,
• τ = thermal protection trip time constant.
rst
• T is 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
When current is less than the dropout level, I
5-282


 ---------------------------- -
t ln 
=
rst rst

Figure 5–154: IEC 255-8 SAMPLE OPERATE AND RESET CURVES
E E
=
n n 1
> 0.97 × k × I
n
L90 Line Current Differential System
2
 

kI
B
 T
+
min
2 2

 
I kI
–
B
> k × I , element starts increasing the thermal energy:
n B
t 
-------------- -
+
–
t
 
op In
, the element starts decreasing the thermal energy:
B
5 SETTINGS
(EQ 5.30)
(EQ 5.31)
GE Multilin