Iec 255-8 Sample Operate And Reset Curves - GE T60 Instruction Manual

5.7 CONTROL ELEMENTS
To ensure element accuracy for high overcurrent conditions, the maximum value of I/(k x I
istically it is exceeding this value.
The reset time of the thermal overload protection element is also time delayed using following formula:
5
In the above equation,
• τ = thermal protection trip time constant
rst
• T is a minimum reset time setting
min
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
5-308


 ---------------------------- -
t ln 
=
rst rst

Figure 5–157: IEC 255-8 SAMPLE OPERATE AND RESET CURVES
E E
=
n n 1
T60 Transformer Protection 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
5 SETTINGS
) is limited to 8, even when real-
B
(EQ 5.51)
(EQ 5.52)
GE Multilin