Does anyone have suggestions for arc-flash hazard labeling of equipment on the secondary side of a Scott connected transformer? The transformer is a "Varivolt" design and the secondary windings deliver a voltage between 72 and 290V. My understanding is that the IEEE 1584 equations apply to three phase systems. SKM does not model Scott connected transformers. Any ideas?

I thought that a Scott 'T 'connection was used to convert 3-Phase to 2-phase. The IEEE 1584 would not apply to the 2-Phase system.

Do you have a standard T connection instead?

This doesn't sound right. The original Scott transformer converts 2 phase 90 degree power to 3 phase and vice versa. There is a T-to-T connected transformer that is a lower cost low kVA transformer that uses two of them back-to-back. But none of these are variable voltage which is what you are describing. That sounds more like a conventional autotransformer with a continuous tap arrangement that I typically see in motor test stands so you just model it as an autotransformer.

Can you recheck your terminology because Scott T transformer is not what you are describing.

Scott T-Connected transformer, 3 phase primary, 2 phase secondary. The transformer has a rotating winding with sliding contacts that act as a tap changer.

The IEEE 1584 standard does not apply to 2-phase systems.

It doesn't apply to single phase either but testing by Mersen and others has shown that single phase arcs aren't that much different from three phase arcs in terms of energy. So applying a 3 phase model would produce a higher result but not that much higher.

Greenwich John,

... just curious, is your Scott T secondary powering direct immersion electrodes for glass furnace? ... use of such a varivolt Scott T secondary is the only method I am familiar with ...

Yes, that is the application.