For Relay setting of any protected unit like HT Motor, it required FLC, CT Primary and secondary and Relay input current.
In almost cases,FLC and CT Primary current never matched.yes, CT secondary and Rated Relay input current are matched.
That’s are like 1000/5 A 930 A or 2000/5 A 1650 A consider, Rated Relay input current is 5A.
So, Protected unit scaling factor =
1000 5
——-X —– = 1.21
5 930
means, when Relay sense 1 A current,that time protected unit will be running at 1.21 times of FLC.
So, Protected unit scaling factor is a multiplication factor used to bridge the gap between FLC and Rated CT Primary current duringRelay setting calculations.
hence, Per unit scaling factor=
CT Py current * Rated Relay current
————— X ———————–
CT Sy current FLC
Smart Motor Protection Relays are automatically calculating this factor after putting all relevant datas.