An impulsive transient may be a sudden, non–power frequency modification within the steady-state condition of voltage, current, or each that's one-way in polarity (primarily either positive or negative).
Impulsive transients are commonly characterized by their rise and decay times that will conjointly be unconcealed by their spectral content. As an example, a 1.2x50µs, a pair of 2000 volt (V) impulsive transient nominally rises from zero to its peak value of 2000V in 1.2µs and then decays to 0.5 its peak price in 50s. The foremost common explanation for impulsive transients is lightning. From the above fig shows a typical current impulsive transient caused by lightning.
Because of the high frequencies concerned, the form of impulsive transients is modified quickly by circuit elements and might have considerably totally different characteristics once viewed from different elements of the power system. They are usually not conducted way from the supply of wherever they enter the power system, though they'll, in some cases, be conducted for quite some distance on utility lines. Impulsive transient’s will excite the natural frequency of power system circuits and turn out periodic transients.