A Method to Predict Transient Constant for Synchronous Machine

Abstract

It is impossible to determine subtransient (transient) reactance and subtransient (transient) short-circuit time constant of middle and large synchronous machines from the sudden three-phase short-circuit test, because it needs a large capacity of equipment to determination of quantities from the test.
Thus, this paper describes a new method which is wield to measures these constants by a simple test using a small D. C. power supply.
The key points of this method are summarized as follows:
(1) D. C. voltage is applied to the armature winding (two terminals with the third one open) of a stationary synchronous machine through a resistance. When two terminals are closed, the winding is short-circuited and the current in the armature winding decays. The whole process of decaying current is recorded.
(2) The value of transient phenomena of the winding calculated from circuit equations (circuit of armature, field winding and damper winding) is compared with actual data, and the unknown equivalent circuit constants can be identified by the least square method.
(3) Transient phenomena of the sudden three-phase short-circuit are calculated by two-reaction theory using identified constant. As a result these transient constants are calculated.
Transient constant of the synchronous machine by the new method almost agrees with the observed values.