How does a MiCOM P63x relay calculate Idiff and Irestrain

Issue
The user would like to calculate the Idiff (differential current) and Ires (restrain current) given the injection currents and matching factors

Product Line
Micom P63x transformer differential relay

Environment
Calculating MiCOM settings

Resolution
The formula below is used by the relay to calculate the Idiff and Irestrain:

To simplify the equations, assume that the Zero-sequence current filtering is disabled :



Where Kam,a and Kam,b are the amplitude matching factors calculated by the relay based on Iref/Inom on side a and side b, respectively. Refer to the differential protection section in the manual for more information.

Example:
I,a,sec = 10 A                     I,nom,secondary= 5 Amps             Kam,a= 2.76
I,b,sec = 5 A (180 deg)        Kam,b= 1.32



Iref is calculated based reference power and the nominal voltage on side a and b.

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