Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

direct-axis subtransient short-circuit time constant
a constant that characterizes the initial decay of transients in the d-axis variables of the synchronous machine with the stator windings short-circuited. The interval characterized is that immediately following a disturbance, during which the effects of amortisseur windings are considered. A detailed (derived) closed-form expression for the subtransient short-circuit time constant of a machine with a single d-axis amortisseur winding is obtained by taking the reciprocal of the largest root of the numerator of the d-axis operational impedance. An approximate (standard) value is often used, in which it is assumed the field winding resistance is small and the detailed expression simplified.
direct-axis transient short-circuit time constant
a constant that characterizes the decay of transients in the d-axis variables of the synchronous machine with the stator windings short-circuited. The interval characterized is that following the subtransient interval, but prior to steady-state, in which the effects of the amortisseur windings are small (possibly negligible). A detailed (derived) closed-form expression for the short-circuit transient time constant is obtained by taking the reciprocal of the smallest root of the numerator of the d-axis operational impedance. An approximate (standard) value is often used, in which it is assumed the amortisseur winding resistance is infinite and the detailed expression simplified.
transient short-circuit
time constant pass and stop bands are critical. A longer filter length generally implies that the filter can have a steeper transition band to a similarly shaped shorter length filter.