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Synchronous motor V-curves

The steady-state characteristics of a synchronous motor represented by phasor diagrams are shown as function of the excitation voltage E: for low values of E, the motor is said to be under excited and the current I lags the terminal voltage V where as, for large values of E, the motor becomes over excited with the current now leading the voltage. Note that the locus of the current phasor is a vertical line meaning that I cos(φ) is constant; similarly the locus of E is a horizontal line satisfying the condition that E sin(δ) is constant.The associated V-curves (I versus E) are also shown.

©M.Riaz