Arc Flash

[SilverArc]

Hi,
This is my first time here and I heard about it from some people I met at an Arc flash analysis tranining session yestarday arranged by a SWGR manf. The speaker was an expereinced guy but I guess he could not get me that feel for my questions that I was hoping. I cruised through this website and I guess there are lot of experts here. I would appreciate, if some of you could spare a moment and throw some answers here.

Q#1, How can we find out a conventional single line to ground fault or a conventional three phase fault will turn in to a single line to ground arcing fault or three phase arcing fault.

Suppose I throw a screwdriver on a bus and it hits all at the same time, so should I consider it as a conventional three phase bolted fault.

If the same screwdriver is thrown in such a way that it touches in a non-uniform way.

What kind of fault will develop into a arc fault and why an arc fault is less than a normal conventional fault.

I am not sure, if these questions just crop up in me or some of you come across these things.

Thanks for your time in anticipation.

 

[RonShap]

Most faults begin as a high impedance fault (arc fault), where the air is part of the faulted circuit.
The NFPA 70E and IEEE 1584 address three phase arc faults.
Your scenarios are feasible, although for analysis, you need to calculate bolted fault currents for AIC selection and arc flash fault currents for use in coordination and PPE selection.

 

[dpc]

Faults are unpredictable, so arc-flash protection is based on worst-case assumptions.

Arcs appear basically as resistance so an arcing fault current will always be lower than for a bolted fault, which by definition has zero impedance at the fault.

Arcing faults are typically initiated by something (or someone) creating a temporary short circuit that is replaced by an arc due to the ionization of the air.

To create arcing faults for testing, a small (#16) piece of wire is connected across all three phases. After the wire melts or is vaporized, you are left with an arcing fault.

 

[SilverArc]

Thanks everybody.

Please advise any company for CAD software for Electrical Power and control schematics. I am aware of Autocad's Electrical module and ECTI.

Please advise, if there is any other company involved in this work.
Thanks

 

[wbd]

You might want to check the Engineering Computer Programs forum on this website for that additional question or do a search as that has been discussed before.

 

[Zogzog]

Why is this guy doing training on arc flash analysis if he couldnt answer those questions? Granted, I would expect most people to answer those, but if they are training on the topic, they should.

BTW, you came to the right place to get your answers, there are some great minds here.