THE THEORETICAL approach so far made in the development of formulas for the direct- and the quadrature-axis subtransient reactances is based on. Subtransient Reactance, usually denoted as X''d, is the reactance used to determine the current during the first cycle after the occurance of the is the difference between subtransient and transient. Leakage armature is the most important share in subtransient reactance and some estimate would be useful. But if you haven't any information put 20% (pu). Author: Gunner Reinger Country: Congo Language: English Genre: Education Published: 10 January 2014 Pages: 701 PDF File Size: 11.14 Mb ePub File Size: 25.83 Mb ISBN: 295-5-67394-918-8 Downloads: 11886 Price: Free Uploader: Gunner Reinger  The subtransient reactance is an impedance value that entirely neglects the resistance component. The quantity depends on the physical characteristics and construction of electric generators. The damper windings stabilize the rotor by inducing an electromagnetic torque that resists undesired subtransient reactance motion.

Though a damper bar benefits the machine by increasing its efficiency and stability, it also introduces subtransient reactance mutual inductance between it and the various other windings. Note on overloads For economic reasons, the thermal motor of a replacement set may be strictly sized for its nominal power.

If there is an active power overload, the diesel motor will stall. The active power balance of the priority loads must take this into account A subtransient reactance set must be able to withstand operating overloads: Saturated Sub-transient reactance of a generator?

In this region it can be expected that the relation between applied test voltages and resulting short-circuit currents is linear, i.

What is transient reactance? - Quora

Unsaturated transient and subtransient reactances can be calculated by the designer quite accurately. The fault current will subtransient reactance in all the three phases of alternator and its waveform will be as shown in figure below. When the alternator is short-circuited, the currents in all the three-phases rise rapidly to a high value of about 10 to 18 times subtransient reactance full load current, during the first quarter cycle.

Subtransient reactance flux crossing the air gap is large during a first couple of cycles. The reactance during these first two or three cycle is least and the short circuit current is high.