GE Multilin UR Series N60 Instruction Manual page 284

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
5-164


 ---------------------------- -
t ln 
=
rst rst

I
Figure 5–73: IEC 255-8 SAMPLE OPERATE AND RESET CURVES
E E
=
n n 1
> 0.97 × k × I
n
N60 Network Stability and Synchrophasor Measurement System
2
 

kI
B
 T
+
min
2 2

 
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 5.15)
(EQ 5.16)
GE Multilin