From Electrical Installation Guide
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 Electropedia
Various types of overvoltage
An overvoltage is a voltage pulse or wave which is superimposed on the rated voltage of the network (see Fig. J1).
Fig. J1: xamples of overvoltage
This type of overvoltage is characterized by (see Fig. 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.
Fig. 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 Fig. 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.