Why inductive load is used in zpf method

This method is also called potier method. In the operation of any alternator, the armature resistance drop and armature leakage reactance drop IXL are actually e.m.f. quantities while the armature reaction is basically m.m.f. quantity. In the synchronous impedance all the quantities are treated as e.m.f. quantities as against this in M.M.F. method all are treated as m.m.f. quantities. Hence in both the methods, we are away from reality.
Note : This method is based on the separation of armature leakage reactance and armature reaction effects. The armature leakage reactance XL is called Potier reactance in this method, hence method is also called potier reactance method.