GE F60 Instruction Manual page 391

5 SETTINGS
The IEC255-8 cold curve is defined as follows:
The IEC255-8 hot curve is defined as follows:
In the above equations,
• t = time to operate.
op
• = thermal protection trip time constant.
τ
op
• I = measured overload RMS current.
• I = measured load RMS current before overload occurs.
p
• k= IEC 255-8 k-factor applied to I
• I = protected element base (nominal) current.
B
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
GE Multilin
 2
I

 ------------------------- -
t ln 
=
op op
2

 
I kI
–
B
2 2

I I
–
p

 ------------------------- -
t ln 
=
op op
2

 
I kI
–
B
, defining maximum permissible current above nominal current.
B
2
   
kI
B


 ---------------------------- - 
t ln
=
rst rst
2 2
 
 
I kI
–
B
F60 Feeder Protection System
5.7 CONTROL ELEMENTS


2



2

T
+
min
(EQ 5.26)
(EQ 5.27)
(EQ 5.28)
5
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