GE MIFII GEK-106237P Instruction Manual page 181

A.5 THERMAL CURVE
A.5THERMAL CURVE
The time needed for an element to rise its temperature (from an initial temperature θ
A
difference between the initial and the final temperature) is called "Time Constant", and it is represented by the letter τ.
Using an equation, it is the time it takes to reach an intermediate temperature θi where:
θ θ
If θ
is the temperature origin, at a given time, the temperature can be written as:
0
Where:
θ
Temperature increase at a given time
θ
N Rated temperature (temperature reached if I = IN)
In Protected element rated current
I Current flowing through the protected element
T Time
τ
Time constant
A-6
τ τ
θ θ
∞ ∞
θ θ
i i
63% 63%
θ θ
0 0
t t
MIFII Digital Feeder Relay
APPENDIX A
) the 63% of θ (θ is the temperature
0
100% 100%
GEK-106237P