Curves X and Y in the figure denote open circuit and full load zero power factor (ZPF) characteristics of a synchronous generator, Q is a point on the ZPF characteristics at 1 p.u. voltage. The vertical distance PQ in figure gives the voltage drop across.

Determination of Voltage Regulation Using the Potier Method

• The MMF method suffers from a few limitations; that is, it does not take into account the leakage reactance drop.(X_al) and the armature resistance drops.
• While the field excitation corresponding to rated O.C. voltage takes saturation into account, the S.C. test does not as it is conducted with less excitation.
• All these shortcomings are overcome with the potier method where the machine supplies rated current to a purely inductive load at rated voltage (ZPF lag) and thus the magnetic circuit is in saturation while supplying the demagnetizing ampere-turns to overcome armature reaction.
   

Potier Method: It lays down a procedure to account for the moves that correspond to the Armature Reaction voltage drop (I_aX_a), leakage reactance voltage drop (IaXal), and resistive voltage drop (I_aR_a)

Explanation: Curve X shows the O.C.C. with saturation effect and Curve Y shows ZPF characteristics considering purely inducting load with purely demagnetizing armature reaction effect. ZPF characteristics are obtained by subtracting Leakage reactance drop from O.C.C. shown by vertical distance FD or (PQ).