What is transient and Subtransient current?

There are three periods of time: – Sub-transient period: first cycle or so after the fault – AC current is very large and falls rapidly; – Transient period: current falls at a slower rate; – Steady-state period: current reaches its steady value. • It is possible to determine the time constants for the sub-transient.

What is meant by Subtransient reactance?

The subtransient reactance, X”d, is the generator internal impedance element that is effective in the first cycles of a transient load event and determines the magnitude of the instantaneous fault current from the generator.

What is the reason for transient during short circuit?

The transient occur due to the trapping of the energy and its subsequent release somewhere in the circuit. Such transients are referred as abnormal current and voltage transients.

How do you find the Subtransient reactance of a generator?

If you wanted to convert its impedance (reactance) to 100 MVA base all you need to do is: impedance on new base = old impedance x (new base / old base) impedance on 100 MVA = 0.16 x (100 / 0.8) = 0.16 x (125)

What is Subtransient period?

First, “subtransient” refers to the fact that this quantity operates extremely fast—faster than even “transient.” In technical terms, the subtransient time period lasts from about one to three cycles, which is from 16.7 milliseconds to 50 milliseconds (assuming a power frequency of 60 Hz).

What is a transient discuss the causes of transients in power system?

Transient voltages and currents are caused by sudden changes within the electric power system. All transients are caused by either connection or disconnection of elements within the electric circuit or injection of energy due to a direct or indirect lightning stroke or static discharge.

What is sub-transient reactance?

This reactance is called subtransient reactance and is denoted by X”. The first few cycles come under sub-transient state. After a first few cycles, the decrement in the r.m.s. value of short circuit current is less rapid than the decrements during the first few cycles.

What is the subtransient reactance of an electric generator?

The quantity depends on the physical characteristics and construction of electric generators. The subtransient reactance is a transient effect that’s directly related to the electromagnetic relationships between the various physical components of the generator.

What is the sub transient period of a generator?

The period immediately after a short circuit on the generator and lasting upto 2-3 cycles, is called sub transient period. The current during this period is highest and is determined by sub transient reactance. The value of sub transient reactance is about half of the leakage reakage reactance.

What is transient energy in Electrical Engineering?

, B.tech Electrical Engineering, Institute of Technical Education and Research (2017) A transient is a short-lived burst of energy in a system caused by a sudden change of state. Transient and sub-transient reactance are generally the terms which appear in the calculation of fault current.