GE D30 Instruction Manual page 336

5.7 CONTROL ELEMENTS
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
In the above equations,
• Δt 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)
• I is the measured overload RMS current at index n.
n
5-204
Figure 5–112: IEC 255-8 SAMPLE OPERATE AND RESET CURVES
E E
=
n n 1
> 0.97 × k × I
n
E E
=
n n 1
D30 Line Distance Protection System
> k × I , element starts increasing the thermal energy:
n B
t 
-------------- -
+
–
t
 
op In
, the element starts decreasing the thermal energy:
B
t 
-------------- -
–
– t
 
rst In
5 SETTINGS
(EQ 5.24)
(EQ 5.25)
GE Multilin