Answer / ravi patel

Plug setting of a relay is the setting of a relay pick up current.
A relay pick up current is defined as the value of current through relay coil at which relay starts to operate.
Generally, it is specified as percentage of relay pick up current.
A relay plug setting (PS) have a value in the given range i.e. 50 to 200% .
Plug setting of 50% means as soon as current through relay coil increases above half (50%) of relay pick up current, it will start to operate.
Similarly, Plug setting of 200% means as soon as current through relay coil increases above two times (200%) the relay pick up current, it will start to operate.
If CT ratio is 300 / 5 A ,
then Relay pick up current (Ip) = 5 A
Thus,
If PS = 100% ,then Ip = 5 A corresponding secondary current = 300 A.
If PS = 50% ,then Ip = 2.5 A corresponding secondary current = 150 A.
If PS = 200% ,then Ip = 10 A corresponding secondary current = 600 A.

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