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.
