PTW32 isn't allowing me to calculate arc flash for single phase equipment. I noticed that the calculations assume a three phase fault, but I figure that I should worry about single phase transformers too, right? Or am I just doing something wrong? Sorry if this is a dumb question.

You need to purchase the single phase module from SKM.

I am using PTW32 too, can anyone explain why I have to use comprehensive SC for Arc fault calculation? What's the big difference if I want to use A_Fault? Thanks!

I just emailed SKM support and they said that the existing standards don't address single phase systems. I haven't read that anywhere, but is this correct?

Noah,

If you haven't already, I would suggest emailing support@skm.com. I don't know enough about SKM yet to be helpful.

Right now the IEEE 1584 models are all three phase. The 1584 standard lists this in Section 5.1 but it is not obvious unless you go looking for it. The reasoning for the three phase model is that although the majority of short circuits (bolted and arcing) on grounded systems might originate as a line-ground event, a line-ground arc flash can quickly escalate into a three phase event almost instantaneously due to the conducting nature of the plasma (a.k.a. fire ball).

For now, three phase models are all that exist within 1584.

A few companies like Kinectrics (Ontario-Hydro) have developed their own single phase models for overhead transmission and distribution lines but for equipment at lower voltages we only have three phase models.

Noah,

I do not know if someone has answered your question or not but I believe the difference is in the fault current magnitude. The fault current magnitude obtained using comprehensive method (which is strictly theoretical) is the same as the ANSI fault during the first half of cycle with small variation in X/R ratio. After that the ANSI multipliers for sources and motor contributions kick in...which eventually reduces the magnitude.

The arc-flash result should remain the same since PTW uses initial symmetrical RMS current (at 1/2 cycle) for its calculations.

Aleen
Burns & McDonnell