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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.
Vd                              the component of V along the d-axis.
Vq                             the component of V along the q-axis.
I                        the stator current.
Id                               the component of I along the d-axis.
Iq                               the component of I along the q-axis.
IRa                            the volt drop due to the armature or stator current.
IdRa                         the component of IRa along the d-axis.
IqRa                        the component of IRa along the q-axis.
IdXd                      the volt drop due to the d-axis synchronous reactance.
IdX’d                       the volt drop due to the d-axis transient reactance.
IdX’’d                     the volt drop due to the d-axis sub-transient reactance.
IqXq                        the volt drop due to the q-axis synchronous reactance.
IqX’q                      the volt drop due to the q-axis transient reactance (normally taken as IqXq ).
IqX’’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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