GE L60 Instruction Manual page 393

5 SETTINGS
Figure 5–137: 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
When current is less than the dropout level, I
In the above equations,
• ∆t is the power cycle duration.
• n is the power cycle index.
• t is the trip time calculated at index n as per the IEC255-8 cold curve or hot curve equations.
op(In)
• t is the reset time calculated at index n as per the reset time equation.
rst(In)
GE Multilin
> k × I
n
t Δ
E E -------------- -
= +
n n 1
t
–
( )
op In
> 0.97 × k × I , the element starts decreasing the thermal energy:
n B
t Δ
-------------- -
E E
= –
n n 1
t
–
( )
rst In
L60 Line Phase Comparison System
5.6 CONTROL ELEMENTS
, element starts increasing the thermal energy:
B
5
(EQ 5.30)
(EQ 5.31)
5-265