GE T60 Instruction Manual page 455

5 SETTINGS
• I = protected element base (nominal) current
B
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:
In the above equation,
• τ = thermal protection trip time constant
rst
• T is a minimum reset time setting
min
Figure 5–156: IEC 255-8 SAMPLE OPERATE AND RESET CURVES
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
GE Multilin
2
 
( kI )
B
τ
×  ---------------------------- - 
t ln
= +
rst rst
2 2
 
( )
I kI
–
B
> k × I
n
T60 Transformer Protection System
5.7 CONTROL ELEMENTS
) is limited to 8, even when real-
B
T
min
, element starts increasing the thermal energy:
B
(EQ 5.52)
5
5-309