GE B30 UR Series Instruction Manual page 310

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:
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
5-184

τ × ---------------------------- -
t ln 
=
rst rst

I
Figure 5–81: IEC 255-8 SAMPLE OPERATE AND RESET CURVES
E E
=
n n 1
> 0.97 × k × I
n
B30 Bus Differential System
2
( ) 
kI
B
 T
+
min
2 2

( kI )
–
B
> k × I , element starts increasing the thermal energy:
n B
t Δ
-------------- -
+
– t
op In ( )
, the element starts decreasing the thermal energy:
B
5 SETTINGS
) is limited to 8, even when real-
B
(EQ 5.16)
(EQ 5.17)
GE Multilin