Low Forward Power

yes.

as low forward power and reverse power trip settings will be same normally.Then low forward power should ACT, at same time of Reverse power (even after synchronisation).

but at after synchronization only reverse power relay act for reverse power condition, why?

Low forward power as it is named see only forward power whether forward power is below some required flow so that motoring action doesn't happen specially during synchronisation. Thus it will remain vigilant for low forward condition. It will operate even during normal operation the power flow is less than required setting and acts before reverse power takeover.

thank you MR. Das

Normally after synchronization, during running any reverse power condition arises(due to low turbine speed or something..) REVERSE power relay will only trips but not low forward power right.