GE D30 Instruction Manual page 376

5.7 CONTROL ELEMENTS
• 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
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
5-240

τ
×  ---------------------------- -
t ln
=
rst rst

Figure 5–119: IEC 255-8 SAMPLE OPERATE AND RESET CURVES
D30 Line Distance Protection System
2

( kI )
B

T
+
min
2 2

( )
I kI
–
B
> k × I , element starts increasing the thermal energy:
n B
5 SETTINGS
) is limited to 8, even when real-
B
(EQ 5.24)
GE Multilin