PHSOR DIAGRAM OF A TWO AXIS SALIENT POLE GENERATOR

Following phasor is phsor diagram of a two-axis salient pole generator.

The following points apply to the drawing of phasor diagrams of generators and motors:-

• The terminal voltage V is the reference phasor and is drawn horizontally.
• The emf E lies along the pole axis of the rotor.
• The current in the stator can be resolved into two components, its direct component along the ‘direct or d-axis’ and its quadrature component along the ‘quadrature or q-axis’.

The emf E leads the voltage V in an anti-clockwise direction when the machine is a generator.

Each reactance and resistance in the machine has a volt drop associated with it due to the stator current flowing through it. Consider a generator. The following currents and voltages can be shown in a phasor diagram for both the steady and the dynamic states.

E the emf produced by the field current If .

V the terminal voltage.

V_d the component of V along the d-axis.

V_q the component of V along the q-axis.

I the stator current.

I_d the component of I along the d-axis.

I_q the component of I along the q-axis.

IR_a the volt drop due to the armature or stator current.

I_dR_a the component of IRa along the d-axis.

I_qR_a the component of IRa along the q-axis.

I_dX_d the volt drop due to the d-axis synchronous reactance.

I_dX^’d the volt drop due to the d-axis transient reactance.

I_dX^’’d the volt drop due to the d-axis sub-transient reactance.

I_qX_q the volt drop due to the q-axis synchronous reactance.

I_qX^’q the volt drop due to the q-axis transient reactance (normally taken as IqXq ).

I_qX^’’q the volt drop due to the q-axis sub-transient reactance.

E^’ the emf behind the transient impedance.

E^’’ the emf behind the sub-transient impedance.

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