Arc impedance

[HamburgerHelper]

Does anyone have a good reference for the impedance of ionized air? I am trying to show that the arc of a certain length would be impossible due to just the impedance of the ionized air.

 

[ZeroSeq]

Impedance of ionized air is highly dynamic and very difficult to calculate. Impedance of air (non-ionized) and its breakdown voltage are well understood and are dependent on many factors like humidity, air pressure, temperature, etc.

 

[ZeroSeq]

Paschen's Law predicts breakdown voltage based on pressure, gap length, and composition of the gas.

https://en.wikipedia.org/wiki/Paschen's_law

 

[DistCoop]

Pretty rough equation here, but

Zarc = (440*length)/I

where length is arc length in feet. A common accepted value of arc voltage drop is 440V/ft. Eventually get to a point where the voltage cannot sustain the arc.

This info is taken from "Electric Power Generation, Transmission, and Distribution", chapter 23 (Hard to Find Information on Distribution System Characteristics and Protection).

 

[mard57]

If you refer to IEEE 1584, there is an equation that calculates arcing current in air (Ia) using the variables of voltage, gap between conductors and 3 phase bolted fault current (Ibf). It is part of the calculations for incident energy Ie measured in cals/cm squared.

From the arcing current and knowing the system voltage, you can get an approximation for the ionized air impedance.

 

[Mbrooke]

I have a similar concern. What is the IEC standard for this?

 

[mard57]

European Standard EN 50110: Operation of electrical installations

The IEEE 1584 calculations should be the same in the European Standard.

 

[Mbrooke]

There is no direct 6xxxx IEC standard?

 

[mard57]

Not sure. You'll have to do some research yourself.