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.