Describe the effects of changing the shaft load 1 Armature C

Describe the effects of changing the shaft load: 1. Armature Current and 2. Power Angle

Solution

•Increasing the strength of the magnets should cause a closer pole alignment and a smaller power angle.

•Assuming a constant shaft load,

–apply a step increase to Ef

–Efsin increases, the rotor accelerates

angle decreases until Efsin has the same value as before (synchronous speed

•IMPORTANT!!!!
–Increasing the excitation from Ef1 to Ef3 caused the angle if the current phasor (and hence the power factor) to go from lagging to leading!
–Normal excitation when power factor = 1
–Excitation greater than normal is known as overexcitation
–Excitation less than normal is known as underexcitation