Sep 8, 2013

Power Quality - Oscillatory Transients

An Oscillatory (periodical) transient may be a fulminant, non–power frequency modification within the steady state condition of voltage, current, or together, that has each positive and negative polarity values.

An oscillatory transient comprises a voltage otherwise current whose instantaneous values changes polarity quickly. It’s delineated by predominate frequency, interval, and magnitude. These predominate frequency subclasses outlined in Table below are low, medium and high frequency. The frequency series for these arrangements are selected to overlap with common forms of power network oscillatory transient sensations.

Oscillatory transients by way of a primarry frequency part larger than five hundred rates and a typical interval measured in microseconds (or several cycles of the principal frequency) are thought of high-frequency transients. These transients are typically the results of a native system response to associate degree impulsive transient.
A transient with a primary frequency part between 5-500 KHz with length measured in the tens of microseconds (or many cycles of the principal frequency) is termed a medium-frequency transient. Succeeding condenser energization leads to periodical transient currents within the tens of kilohertz as illustrated in Figure. Cable switching leads to periodical voltage transients in the same frequency vary. Medium-frequency transients can even be the results of a system response to associate degree impulsive transient.

A transient with a primary frequency part less than five rates, and a length from 0.3 to 50 ms, is taken into account a low-frequency transient. This class of phenomena is often encountered on utility sub transmission and distribution systems and is caused by many sorts of events. The foremost frequent is condenser bank energization, which typically leads to associate degree periodical voltage transient with a primary frequency between 300 and 900 Hertz. The height magnitude will approach a 2.0 pu, however is usually 1.3 to 1.5 chemical element with a length of between 0.5 and three cycles counting on the system damping.

Oscillatory transients with principal frequencies less than three hundred Hertz can even be found on the distribution system. These are usually associated with Ferro resonance and electrical device energization. Transients involving series capacitors may additionally fall under this class. They occur once the system responds by ringing with low frequency elements in the electrical device influx current (2 & 3 harmonic) or once uncommon conditions end in Ferro resonance.

It is additionally attainable to reason transients (and different disturbances) per their mode. Basically, a transient in an exceedingly three-phase system with a separate neutral conductor will be either common mode or normal mode, counting on whether or not it seems between line or neutral and ground, or between line and neutral.


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