Saturday, February 9, 2013

The Equivalent Circuit and a Simplified Phasor Diagram for a Phase of a Synchronous Generator

The Equivalent Circuit and a Simplified Phasor Diagram for a Phase of a Synchronous Generator

The equivalent circuit answering the equation of electric slate of a stator phase of a synchronous generator is shown in Fig 4 a. Now we will construct a phasor diagram for a phase of a synchronous generator. To do this, we choose as reference the main flux linkage vector Ψ̇0 which is directed to the left along the axis of abscissae .

(Fig 4 b). The phasor of Ė0 induced by Ψ̇0 is in quadrature lagging with Ψ̇0 .The phasor of the stator (armature) current is lagging £0 by an angle φ0 determined by the relative magnitudes of the reactances and resi­stances

φ0 = arc tan ( + load)/(rw + rload)      (15.4)

where load and rload are the reactance and resistance of the generator load.

The Equivalent Circuit and a Simplified Phasor Diagram for a Phase of a Synchronous Generator

The phasor of voltage rw is aligned with the current phasor , and the voltage phasor j is in quadrature leading with it. The phasor of the terminal voltage per phase, can be located by sub­tracting the sum of the voltage phasors across the resistance and reactance per phase from E0 :

= Ė0 - j - rw

On joining the tips of the phasors E0 and , we obtain a triangle of voltages across the resistance and inductive reactance per phase , with Zwas hypotenuse.

The phasor rw is shown on an exaggerated scale to make the diagram more instructive.