DPR-400 User Manual Rev_01 Firmware V-1.0
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The DPR-400 controller offers constant time and 12 different variable time curves for protection functions.
Current / time curves are usually calculated using the equation below:
Here:
t(I) = Trip time as a function of input current I
I = Instantaneous secondary current value of the phase
Is = Fault threshold for secondary current
T = Time coefficient (TD for IEEE, TMS for IEC)
β = Constant for the given curve
α = Constant for the given curve
L = Constant for IEEE, 0 for IEC
C = Constant additional delay