Looking into an electric arc furnace with the power on
What you're seeing here is the arc between the tip of an electrode and liquid steel, which is hidden under nearly a foot of synthetic lava (aka slag - the bubbling liquid you see here). This video was recorded entirely by chance, I was videoing other things when I realised that I had a clear view of 'A'-phase. I had to use two crossed polarised filters in order to block out enough light to see things clearly - and yet the arc itself is still blue-white and indistinguishable! Just keep in mind that the liquids seen in the furnace look white-hot to the naked eye.
The furnace is three-phase AC with the other two phases hidden. Phase-to-phase voltage was about 1000V, phase-to-ground voltage was about 400V, which resulted in an arc about 350mm long. The transformer was rated at 72MVA and active power was around 55 megawatts. The arcs carried about 50 kiloamps of current.