# Corona discharge insulation

If a wire is insulated from arcing up to 10 kilovolts, is it insulated up to twice that much from corona discharge? Because I’m imaging that for corona discharge to occur, the electricity has to flow outwards by the repulsion of like charge, so it would have to flow through two 10 kv wire insulation layers. So one like charge would be pushed out through one direction while another like charge is pushed through the insulator in the opposite direction, making it as if the barrier was insulated to 20kv.

No,it doesn't work that way. Charge and voltage are two separate things. 10 kV is 10 kV, and whether it results in an arc or corona discharge (also a kind of arc) is irrelevant.

Separation of charges results in an electric field. "Voltage" is one way of describing the potential energy of charges in that field.

Corona discharge and other kinds of arcs occur when the electric field intensity (a function of both voltage and geometry) becomes high enough to strip electrons off of atoms in the air (or other insulator).

If a wire is insulated from arcing up to 10 kilovolts, is it insulated up to twice that much from corona discharge?

No, but if you mean impulse levels, that can trigger corona, "Perhaps yes". It depends how you define the impulse and the material properties like RLC. But even DC can trigger corona as this is only caused by contaminated materials less than ideal between an electric field , E [V/m]( some Voltage per meter or mV/μm of stress)

There are many dielectric test conditions, applied waveforms and definitions for insulation.

a) Dielectric withstanding test , a DC and/or an AC voltage with low frequency and a permitted leakage current at @25'C. This is the steady state rating with some margin, but new & clean, there may be a tolerance for any environmental stress conditions in design verification tests like 2x.

b) *Transient immunity** This increases the threshold and the voltage but shortens the time duration to simulate an impulse like shaped tail-voltage induced by lightning. In Power Engineering terms, this is called the Basic Insulation Level or BIL and parts may have ratings like BIL200 can withstand 200kV impulse yet maybe only 50 kVac.

When dielectrics breakdown due to transient charge flow, it is actually an avalanche effect, like snow on a mountain, where the material is bound together until a force is high enough to start a separation under high electric field forces. Once one part moves and creates a vibration, it triggers others to separate until a big cluster moves easily and zap, the sound effect when the charges detonate at the speed of sound colliding with the conductor it was attracted to.

We call corona this visible or audible effect , but actually it is like a relaxation oscillator or a combustion engine with repetitive zaps of charge build up, partial discharge, avalanche effect with more charges accelerating at the maximum speed of medium, then detonation and then repeating this cycle over again.

Static electricity (and corona discharge) does not respect circuit diagrams; it is possible for the electric field around a wire to grow so that it ionizes air, and even if insulation can stand that field, air cannot. Insulation (unlike grounded metal shielding) does not stop electric fields.

Corona discharge (aka St. Elmo's fire) around a wire represents currents, perhaps very small currents, radiating outward from the wire through the insulation to the air, through only one thickness of insulation. Ionized air can transport the charge to just about any near-grounded item (slowly) to replace the charge on the wire, thus completing a 'circuit'. Once ionized, air is no longer a nonconductor (until it discharges).

Ionized air is very corrosive, and can degrade insulation; before wide use of silicones, auto spark plug wiring needed frequent replacement because of this. So, even GOOD insulation won't necessarily stay intact if corona discharge is initiated.