GE Digital Energy L30, Instruction Manual, Page: 343 / 644

GE Multilin L30 Line Current Differential System 5-217
5 SETTINGS 5.7 CONTROL ELEMENTS
5
The IEC255-8 cold curve is defined as follows:
(EQ 5.23)
The IEC255-8 hot curve is defined as follows:
(EQ 5.24)
In the above equations,
• t
op
= time to operate.
• τ
op
= thermal protection trip time constant.
• I = measured overload RMS current.
• I
p
= measured load RMS current before overload occurs.
• k = IEC 255-8 k-factor applied to I
B
, defining maximum permissible current above nominal current.
• I
B
= protected element base (nominal) current.
The reset time of the thermal overload protection element is also time delayed using following formula:
(EQ 5.25)
In the above equation,
• τ
rst
= thermal protection trip time constant.
• T
min
is a minimum reset time setting
t
op

op
I
2
I
2
kI
B
 
2
–
--------------------------
 
 
 
ln

=
t
op

op
I
2
I
p
2
–
I
2
kI
B
 
2
–
--------------------------
 
 
 
ln

=
t
rst

rst
kI
B
 
2
I
2
kI
B
 
2
–
-----------------------------
 
 
 
ln

T
min
+ =