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'''overvoltage''' (in a system) 

any voltage between one phase conductor and earth or between phase conductors having a peak value exceeding the corresponding peak of the highest voltage for equipment  

definition from the International Electrotechnical Vocabulary (IEV 604-03-09); available on [https://www.electropedia.org/] 

== Various types of overvoltage  ==

An overvoltage is a voltage pulse or wave which is superimposed on the rated voltage of the network (see {{FigRef|J1}}). 

{{FigImage|DB422460_EN|svg|J1|Examples of overvoltage}}

This type of overvoltage is characterized by (see {{FigRef|J2}}): 
*the rise time tf (in μs); 
*the gradient S (in kV/μs).

An overvoltage disturbs equipment and produces electromagnetic radiation. Moreover, the duration of the overvoltage (T) causes an energy peak in the electric circuits which could destroy equipment. 

{{FigImage|DB422461_EN|svg|J2|Main characteristics of an overvoltage}}

Four types of overvoltage can disturb electrical installations and loads: 

*Switching surges: high-frequency overvoltages or burst disturbance (see {{FigRef|J1}}) caused by a change in the steady state in an electrical network (during operation of switchgear).

*Power-frequency overvoltages: overvoltages of the same frequency as the network (50, 60 or 400 Hz) caused by a permanent change of state in the network (following a fault: insulation fault, breakdown of neutral conductor, etc.).

*Overvoltages caused by electrostatic discharge: very short overvoltages (a few nanoseconds) of very high frequency caused by the discharge of accumulated electric charges (for example, a person walking on a carpet with insulating soles is electrically charged with a voltage of several kilovolts).

*Overvoltages of atmospheric origin.