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 Post subject: New to arc flash analysisPosted: Tue Jan 19, 2010 3:27 pm

Joined: Tue Jan 19, 2010 2:50 pm
Posts: 3
Hello,
Im currently completing a 12 week professional work placement as part of my uni degree (just finished 3rd year Electrical)

One of the tasks assigned to me is research about how to complete an arc flash analysis of one of the plants.

Well ive read a bunch of articles and the IEEE standard; ive collected all the single line diagrams of the plant.

Ive done a short circuit analysis with the help of another engineer.

Now Im looking at calculating the incident energies. Using the IEEE Std1584-2002 calculations Ive created an excel spreadsheet to take the variables and spit out a result (see attachment)

Just a few questions I have about the results and what they mean

Question 1
Say you’re trying to find the incident energy on a MCC, so you find the fault level of the bus, put it into the calculator and find incident energy. How do you factor in the enclosure? Say the operator is turning a switch on the front of the panel from off to on, what energy will he be exposed to if there is an incident? As they are in the flash protection boundary?

Question 2
In one of our Switch rooms, there are the circuit breakers for some of our motors (in the range of 16MW), these large oil filled breakers must be manually racked in and out. I was wonting to know if the oil would influence the results in anyway?

I might not understand correctly what it means to work on equipment/when to wear the PPE required for that incident energy.

I was also trying to get the demo of EasyPower working but ill have to go through the tutorials a bit more

Cheers
Simon.

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 Post subject: Posted: Wed Jan 20, 2010 5:52 am
 Sparks Level

Joined: Mon Nov 23, 2009 6:37 am
Posts: 51
Location: Tampa, FL
SimonD wrote:
Hello,
Im currently completing a 12 week professional work placement as part of my uni degree (just finished 3rd year Electrical)

One of the tasks assigned to me is research about how to complete an arc flash analysis of one of the plants.

Well ive read a bunch of articles and the IEEE standard; ive collected all the single line diagrams of the plant.

Ive done a short circuit analysis with the help of another engineer.

Now Im looking at calculating the incident energies. Using the IEEE Std1584-2002 calculations Ive created an excel spreadsheet to take the variables and spit out a result (see attachment)

Just a few questions I have about the results and what they mean

Question 1
Say you’re trying to find the incident energy on a MCC, so you find the fault level of the bus, put it into the calculator and find incident energy. How do you factor in the enclosure? Say the operator is turning a switch on the front of the panel from off to on, what energy will he be exposed to if there is an incident? As they are in the flash protection boundary?

Question 2
In one of our Switch rooms, there are the circuit breakers for some of our motors (in the range of 16MW), these large oil filled breakers must be manually racked in and out. I was wonting to know if the oil would influence the results in anyway?

I might not understand correctly what it means to work on equipment/when to wear the PPE required for that incident energy.

I was also trying to get the demo of EasyPower working but ill have to go through the tutorials a bit more

Cheers
Simon.

The calculations that you did indicate a selection for an arc that occurs in a box or for an arc that occurs in open air, the box being switchgear, bucket, etc. The box will focus the incident energy towards the worker, while a arc that occurs in open air will radiate this energy 360 degrees.
The oil in the circuit breaker is the arc extinguishing medium, and has an effect on the AIC rating. It also acts as a heat sink when an arc is formed during normal or fault operations.
When working on a piece of electrical equipment, it can be in one of two states: electrically safe (isolated and tested for the absence of potential and if needbe grounded) or energized. The labels indicate the incident energy and/or the HRC for work on energized equipment or when verifying the absence of potential to place it in an electrically safe condition. The PPE on the label is the minimum level of protection that is required for work on an energized piece of equipment. This information is provided for the qualified worker.
When you get thorugh the tutorial for easypower you may understand what goes into doing the arc flash hazard analysis. It involves more then just entering numbers that you get off of nameplates. You must make some carefully considered engineering judgement when determining the operating parameters that apply to your particular situation.
Work with your engineer to determine how you should proceed.

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 Post subject: Posted: Wed Jan 20, 2010 1:16 pm
 Sparks Level

Joined: Tue Feb 24, 2009 7:05 am
Posts: 252
SimonD wrote:
Question 1
Say you’re trying to find the incident energy on a MCC, so you find the fault level of the bus, put it into the calculator and find incident energy. How do you factor in the enclosure? Say the operator is turning a switch on the front of the panel from off to on, what energy will he be exposed to if there is an incident? As they are in the flash protection boundary?

You factor the enclosure as an arc-in-a-box, which increases the incident energy. There's no lowering of the incident energy for an enclosed arc based on IEEE 1584. For arc-rated enclosures, use what the vendor says (if doors are closed and latched, and the released energy is in the range the enclosure can withstand).

SimonD wrote:
Question 2
In one of our Switch rooms, there are the circuit breakers for some of our motors (in the range of 16MW), these large oil filled breakers must be manually racked in and out. I was wonting to know if the oil would influence the results in anyway?

There's no increase in incident energy in IEEE 1584 for oil-filled circuit breakers.
That doesn't mean there's no hazard. So you could maybe look at remote racking solutions to better protect your people.

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 Post subject: Posted: Wed Jan 20, 2010 1:38 pm

Joined: Tue Jan 19, 2010 2:50 pm
Posts: 3
Hello, thank you for getting back to me.

Ill be working through the easypower stuff today, i didn't get a chance yesterday. ill be back on later incase i run into any more problems.

Cheers
Simon.

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 Post subject: Posted: Wed Jan 20, 2010 2:22 pm
 Arc Level

Joined: Thu Jan 10, 2008 8:49 pm
Posts: 510
Location: New England
"...Say the operator is turning a switch on the front of the panel from off to on, what energy will he be exposed to if there is an incident?"

If you mean something like an on/off or start/stop button, then the operator should be doing so with doors closed. If the device being operated is NOT switching high energy, then there is no live work or PPE required. If it is high energy, then the door offers not protections.

Read my response to a similar question:

If you own Easy Power call them and tell them you want this manual:

They wrote it so you should have no difficulties getting it.

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 Post subject: Posted: Tue Feb 02, 2010 8:52 am

Joined: Wed Dec 16, 2009 11:05 am
Posts: 1
SimonD wrote:
Hello,
Im currently completing a 12 week professional work placement as part of my uni degree (just finished 3rd year Electrical)

One of the tasks assigned to me is research about how to complete an arc flash analysis of one of the plants.

Well ive read a bunch of articles and the IEEE standard; ive collected all the single line diagrams of the plant.

Ive done a short circuit analysis with the help of another engineer.

Now Im looking at calculating the incident energies. Using the IEEE Std1584-2002 calculations Ive created an excel spreadsheet to take the variables and spit out a result (see attachment)

Just a few questions I have about the results and what they mean

Question 1
Say you’re trying to find the incident energy on a MCC, so you find the fault level of the bus, put it into the calculator and find incident energy. How do you factor in the enclosure? Say the operator is turning a switch on the front of the panel from off to on, what energy will he be exposed to if there is an incident? As they are in the flash protection boundary?

Question 2
In one of our Switch rooms, there are the circuit breakers for some of our motors (in the range of 16MW), these large oil filled breakers must be manually racked in and out. I was wonting to know if the oil would influence the results in anyway?

I might not understand correctly what it means to work on equipment/when to wear the PPE required for that incident energy.

I was also trying to get the demo of EasyPower working but ill have to go through the tutorials a bit more

Cheers
Simon.

Simon
You need to work very carefully and within the safety rules of your company - get a copy from your safety rep. This is really not an arc flash issue, its much more onerous situation.

Your 15kV max, 11kV nominal system has a SC level of close to 750MVA at the top end, Your 132kV primary system has an approx 5000MVA SC level. Both are utility level values and hence the Work to Rule Safety advice.

An oil CB is an obsolete and potentially hazardous device in a metalclad or metal enclosed enclosure. OCBs while generally reliable are probably 30 - 40 years old, may not be properly maintained, are reaching their end of life and when they fail it can be explosively, with resultant fire and most likely will destroy associated switchgear and surrounding equipment (hopefully no staff will be within 30 - 40 m) Compounding the safety issue is the (most likely) open door racking in/out process.

The MV OCB should be replaced by safer Vacuum or SF6 breakers. Your metalclad switchgear should be either replaced by, or retrofitted with arc resistance features meeting ANSI C37 20 7, Type B (min) arc resistance requirements including through the door racking. Arc products to be vented safely outside the building Arc resistance means you can work relatively safely in front of the multi point latched dead front door, with an internal arc @ 28kA in the cell. It does not offer the same degree of protection if a CB explodes within the cell and certaintlt not an exploding OCB.

Hope this gets you thinking a little more big picture.

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