Transients due to nearby lightning or switching events can cause degradation or failure of almost any electrical equipment. Impulsive transients can pass through transformer interwinding capacitance to appear on the low side without being reduced by the transformer turns ratio.

Transients can also cause overvoltage tripping of adjustable-speed drives. Oscillatory transients are generally lower in peak voltage but travel further through a distribution network, and are often present throughout a feeder.

IEEE Std 1159-2019, “Recommended Practice for Monitoring Electric Power Quality”, defines and classifies different categories and subcategories of transients. These categories are described here.