Zero power factor curve

The zero power factor curve (also zero power factor characteristic, ZPF, ZPFC) of a synchronous generator is a plot of the output voltage as a function of the excitation current or field using a zero power factor (purely inductive) load that corresponds to rated voltage at rated current (1 p.u.). The curve is typically plotted alongside the open-circuit characteristic.

A diagram with multiple synchronous machine curves; Zero power factor curve is the middle

Obtained by measuring the terminal voltage when the current has a zero power factor current using a pure inductive load that could be regulated to compensate the reactive power of the generator EMF.^[1]

The curve is obtained by rotating the generator at the rated RPM with the output terminals connected to the unity load, varying the excitation field and recording the output voltage.^[discuss]

Potier Triangle

The ZPFC could be used together with the open-circuit saturation curve in Potier Triangle method.

The zero power characteristic is similar to the open-circuit characteristic but shifted down by ${\displaystyle \alpha }$.^{[clarification needed]}