GE Digital Energy L30, Instruction Manual, Page: 344 / 644

5-218 L30 Line Current Differential System GE Multilin
5.7 CONTROL ELEMENTS 5 SETTINGS
5
Figure 5–107: 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
n
> k × I
B
, element starts increasing the thermal energy:
(EQ 5.26)
When current is less than the dropout level, I
n
> 0.97 × k × I
B
, the element starts decreasing the thermal energy:
(EQ 5.27)
In the above equations,
• Δ t is the power cycle duration.
• n is the power cycle index.
• t
op ( In )
is the trip time calculated at index n as per the IEC255-8 cold curve or hot curve equations.
• t
rst ( In )
is the reset time calculated at index n as per the reset time equation.
• I
n
is the measured overload RMS current at index n .
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E
n
E
n 1
–
t

t
op In
 
---------------
+ =
E
n
E
n 1
–
t

t
rst In
 
---------------
– =