Explain the Power Chart

The phasor diagram shown in Figure with the x and y axes added, as shown. This diagram may be converted to a 'power chart' by multiplying each phasor in the diagram by V_R / Z, as shown in Figure, where Z is the impedance of the line.  This shifts the diagram by the element impedance angle (ψ) and changes the units to (volts)² / (ohms), i.e. to VA units. The 'x' and 'y' axes are then scaled directly in Watts and VAr's respectively.

For a constant V_R the scale of the diagram remains fixed and the sending end voltage (V_S) and load angle (δ) are readily estimated for various power and VAr flow conditions.