Answer :
Final answer:
The plug setting multiplier (PSM) can be calculated using the fault current, relay setting, and the CT ratio. After computing the relay setting current given the 50% setting and 400/5 CT ratio, the PSM is found to be 50 when applying the fault current of 2000 A. The correct option is C
Explanation:
To calculate the plug setting multiplier (PSM), you need to use the actual fault current, the relay setting percentage, and the current transformer (CT) ratio. The plug setting multiplier is defined as the ratio of the fault current in the relay coil to the relay setting current.
The relay setting current is derived from the relay setting percentage and the CT ratio. With a relay setting of 50% and a CT ratio of 400/5, first, we calculate the relay current setting:
- Relay setting current = Relay setting percentage × (CT primary current / CT secondary current)
- Relay setting current = 50% × (400 A / 5 A) = 50% × 80 A = 40 A
Once we have the relay setting current, we can find the PSM:
- PSM = Fault current / Relay setting current
- PSM = 2000 A / 40 A = 50
Therefore, the plug setting multiplier will be 50.
