There are various categories of transients, the most common and most troublesome is the high voltage transient spike. These have the potential to damage or destroy equipment, but fortunately if done correctly preventative solutions are relatively inexpensive and easy to apply.
Overvoltage transients are also commonly referred to as “spikes” which is a less technically correct name, but is a more easily understood. Transients can exist for as short a time as a few microseconds but can reach very high values. There are several causes, but the most common cause tends to be lightening strikes on or near an electricity distribution network. Transient over-voltages are typically controlled by good insulation coordination and effective surge suppression at various points in the network.
Additional surge protection can also be installed at the customers main switch-board and on the terminals of various equipment, should the need arise. (Oscillatory transients are not discussed here as an individual topic as they tend not to be particularly harmful, but can be a bit of an issue where utilities switch large capacitors in and out of circuit.)