physics Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which r ...

, Peek's law defines the electric potential gap necessary for triggering a

corona discharge A corona discharge is an electrical discharge caused by the ionization of a fluid such as air surrounding a conductor (material), conductor carrying a high voltage. It represents a local region where the air (or other fluid) has undergone e ...

between two wires: ::

e_v = m_v g_v r \ln \left ( \right )

''e''_v is the "visual critical corona voltage" or "corona inception voltage" (CIV), the voltage required to initiate a visible corona discharge between the wires. It is named after Frank William Peek (1881–1933). ''m''_v is an irregularity factor to account for the condition of the wires. For smooth, polished wires, ''m''_v = 1. For roughened, dirty or weathered wires, 0.98 to 0.93, and for

cable Cable may refer to: Mechanical * Nautical cable, an assembly of three or more ropes woven against the weave of the ropes, rendering it virtually waterproof * Wire rope, a type of rope that consists of several strands of metal wire laid into a hel ...

s, 0.87 to 0.83, namely the surface irregularities result in diminishing the corona threshold voltage. ''r'' is the

radius In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...

of the wires in cm. ''S'' is the distance between the center of the wires. ''g''_v is the "visual critical" electric field, and is given by: ::

g_v = g_0 \delta \left ( 1 +  \right )

δ is the air density factor with respect to SATP (25°C and 76 cmHg): ::

\delta =

''g''₀ is the "disruptive electric field." ''c'' is an empirical dimensional constant. : The values for the last two parameters are usually considered to be about 30-32 kV/ cm (in air) and 0.301 cm^½ respectively. This latter law can be considered to hold also in different setups, where the corresponding voltage is different due to geometric reasons.

References

* {{cite book , first=F.W. , last=Peek , title=Dielectric Phenomena in High Voltage Engineering , url=https://archive.org/details/dielectricpheno00peekgoog , publisher=McGraw-Hill , year=1929
High Voltage Engineering Fundamentals
E.Kuffel and WS Zaengl, Pergamon Press, p366 Plasma physics