As reactance relays are affected by power surges more than impedance relays and mho relays, they are not suitable for longer lines. The effect of power surges stay for a longer period in case of long lines and hence, a relay which is least affected by a power surge is preferred for the protection of long lines. The MHO relay is less affected by power surges than the impedance and reactance relay and hence, it is best suited for the protection of long lines against phase faults.

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