# Does electrical arc with the same power have same temp?

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1. Mar 22, 2016

### kevin_tee

Does electrical arc with the same power but different voltage and current have same temperature?

When electrical arc is form, it is estimate that the temperature is about 3000K
Does temperature depend on voltage or current alone? Or does it depend on power(P=VA)? I think it is power, because temperature depend on the energy (E=P/t). Thanks.

2. Mar 27, 2016

### Jeff Rosenbury

I doubt it.

What people commonly mean by temperature doesn't really apply in a gas plasma. To measure such a temperature, you first need to define what temperature is. Commonly this would be defined to be similar to other states of matter, so PV=nRT would likely still hold.

Since the pressure (P) would depend on the magnetic confinement, the temperature would vary with the magnetic field and thus the current. This would likely include local variations in the field strength as well as global variables. In other words, the temperature would seem to vary within a single arc as well as between arcs. (In air, somewhat random interactions with wind, humidity, etc. will affect the shape of the path of the arc, and thus its magnetic field.)

Anyway, that's my opinion, though I could be persuaded otherwise if someone has a better model. I may be ignorant of better definitions of temperature for gas plasmas for example.

3. Mar 27, 2016

### Baluncore

Probably yes, it is power that ionises the gas. Voltage and current are set by the external circuit.

The temperature is actually dependent on many things. Once the arc strikes and ionisation occurs, the arc voltage will drop and the current will increase. That is a negative resistance effect that must be dynamically countered with series inductance or resistance to keep the arc operating. Temperature will in part be decided by the method used to limit current while maintaining the current flow.

The temperature of the arc is set by an equilibrium between heat generation as W = V * I and the rate of heat loss by radiation. If heat could not escape as fast as generated, then the arc would get hotter and more conductive.

The properties of the ionised gas and the thermal transmission characteristics of the surrounding gas will in part determine the temperature. There is some temperature stability because rising temperature feeds back to increase ionisation and so increase conductivity, which lowers arc voltage to that needed to maintain ionisation. So the arc temperature is determined by the temperature needed to ionise the gas employed.