What is subtransient reactance

The subtransient reactance is an impedance . The reactance during these first two or three cycle is least and the short circuit current is high. This reactance is called subtransient reactance and is denoted by X. The first few cycles come under sub-transient state. An important factor in determining the mag.

Generator reactances are used for two distinctly different purposes.

One use is to calculate the flow of symmetrical short circuit current in coordination studies.

A second use for generator reactances are in specifications that limit the sub- transient reactance to or less in order to limit the voltage distortion induced by . Synchronous Generator Subtransient Reactance. General features regarding transient reactance are listed below. Initial ac component of short circuit current is determined by the leakage. Transient reactance is usually expressed by the symbol X´d. Initial dc component is determined by the instant of . CALCULATION OF SUB-TRANSIENT , TRANSIENT , STEADY STATE REACTANCE – PART – SUB-TRANSIENT REACT.

During first few cycles reactance of synchronous machine is least and short circuit current is highest. This stage is called subtransient reactance. We use transient reactance and the Voltage behind it for Stability Studies as we are interested in conditions after the fault occurs to find the critical clearing time or angle because if the fault is not cleared the system may go into unstable condition.

We use sub-transient reactance and the Voltage behind it for Fault analysis as . To understand the behavior of an alternator under transient conditions, the armature and field resistance is assumed to be negligibly small. Thus, constant flux linkage theorem can be applied. As per this theorem, in purely inductive circuit, the total flux linkage cannot be changed instantneously at the time of any disturbance.

State estimation applied to synchronous generators. A typical transient voltage dip upon load application is pictured in Figure 1. This trace shows the RMS (root mean square) phase voltage of the generator set output. First: No, transient and subtransient reactance is not the same. Power system fault analysis - Duration: 9:55. The method of symmetrical components requires sequence reactances, and an accurate theory of transients requires transient and subtransient reactances and time constants.

Most of the published discussion on the constants has been concerned with the application, rather than the calculation of values. Machine Base used for per unit impedances. Winding Configuration (i.e.

Delta, Grounded Wye, etc). Neutral Impedance (If applicable). Quadrature-axis Sub-transient Reactance (X”q), per unit. Open-circuit saturation with slip rings. Zero power factor saturation curve.

Summation of losses ( efficiency test). Negative-sequence reactance (X2). Direct axis synchronous reactance (XD). T”dand T” qare the d-axis and q-axis subtransient open-circuit time constants.

Efd is the per-unit field voltage using the exciter model nonreciprocal per-unit system. For synchronous machine models, there are d-axis and q-axis reactance values. The following two relationships must .