Reactance Quadrature axis

A similar situation occurs when the rotor pole axis is at right angles to the axis of the stator coils. Here the magnetic reluctance is at its maximum value due to the widest part of the air gap facing the stator coils. The complete reactance in this position is called the quadrature axis synchronous reactance Xsq . Deducting Xa results in the quadrature axis reactance X. ... 

The situation is different when the rotor poles are at right angles to the stator coils. There is no induction in the fleld circuit and the reluctance is high, being almost the same as for the steady state condition. In this situation the corresponding quadrature axis transient reactance X approximately equals the reactance Xq. Cylindrical rotors of two-pole high speed generators have a nearly uniform rotor diameter and almost constant air gap all around the periphery. Hence the reactance X is almost equal to X. ... 

By the same reasoning as for the transient reactances so the sub-transient reactances are derived, and are called the direct axis sub-transient reactance X and the quadrature axis subtransient reactance X" . 

The suffix d relates to the direct axis values, i.e. those that can be represented along the pole axis of the excitation winding. Occasionally, the quadrature axis reactances are encountered and these are denoted by the suffix q. See Chapter 3 for a further discussion of the "d and q axis parameters. 

The quadrature axis reactances are those that can be represented on an axis at right angles to the pole or direct axis. These reactances do not normally appear in the hand calcnlation of fanlt currents. 

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