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 Post subject: IEEE 1584 -2018 - Gaps Between Conductor
PostPosted: Tue Nov 26, 2019 6:43 am 

Joined: Tue Nov 26, 2019 6:36 am
Posts: 5
Hello,

I have a question regarding the the Gap between the conductor.
As you know, in a switchboard the main bus will have a bigger distance between electrodes if compared with the electrodes that connected to the protection unit.
Is this Gap related to the electrode configuration, VCB, VCBB, etc?
Or is this Gap related to the main bus of the swithboard?

Thanks,
Fluffy Bunny Feet


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 Post subject: Re: IEEE 1584 -2018 - Gaps Between Conductor
PostPosted: Tue Nov 26, 2019 8:29 am 
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Joined: Mon Jan 18, 2010 11:35 am
Posts: 523
Location: Wisconsin
The gap would be related to the point where the arcing is.

In a switchboard there could be an extremely large number of possible arcing points, each with their own gap and electrode configuration.

I don't know of anyone that puts lots of effort into fine tuning their calculations. I believe most people simply use the default gaps and 2 or 3 electrode configurations, in an effort to determine a worst case condition.


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 Post subject: Re: IEEE 1584 -2018 - Gaps Between Conductor
PostPosted: Tue Nov 26, 2019 10:03 am 

Joined: Tue Nov 26, 2019 6:36 am
Posts: 5
Hey,
thanks for the feedback.

Should not be related with the protection unit? Since the incident energy depends on T ( tripping time), the gap between the electrodes should not be the Gap in Iarc calculation?

I don't understand why we should relate with the busbar between the cubicles if there is no protection to clear the fault...

What is your opinion?


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 Post subject: Re: IEEE 1584 -2018 - Gaps Between Conductor
PostPosted: Tue Nov 26, 2019 1:44 pm 
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Location: Scottsdale, Arizona
Many years ago, I asked if people use the standard gaps from IEEE 1584, it was almost unanimous that people do.

Some of the reasons:

Is someone really going to measure the equipment
There are multiple gaps for any give piece of equipment

This ties into the 2018 Edition. Back in the first year or 2 of the 2002 Edition, people were second guessing everything as there was only minimal guidance. Similar to what we have today with the 2018 Edition. But, just like 2002, it is slowly getting sorted out.


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 Post subject: Re: IEEE 1584 -2018 - Gaps Between Conductor
PostPosted: Tue Nov 26, 2019 2:48 pm 

Joined: Tue Nov 26, 2019 6:36 am
Posts: 5
Hi Jim,

can you please help me in this question?
I can have all the measurements, gaps, distances in a specific switchboard, no problem.

I just want to understand this GAP issue, Is my understanding correct, can you please give me some guidance?

Thanks


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 Post subject: Re: IEEE 1584 -2018 - Gaps Between Conductor
PostPosted: Wed Nov 27, 2019 1:22 pm 
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JBD wrote:
The gap would be related to the point where the arcing is.

In a switchboard there could be an extremely large number of possible arcing points, each with their own gap and electrode configuration.

I don't know of anyone that puts lots of effort into fine tuning their calculations. I believe most people simply use the default gaps and 2 or 3 electrode configurations, in an effort to determine a worst case condition.


JBD Sums it up quite well. I attached a photo from a test set up in the lab. The gap (from the lab) is the distance between the conductors (copper rods in this case).

As JBD stated, there can be many different gaps for a single piece of equipment so most use the IEEE 1584 (software) defaults based on equipment type/class.

If you want to change the gap in the calculations you can do that as long as it is within the range of applicability of IEEE 1584.


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 Post subject: Re: IEEE 1584 -2018 - Gaps Between Conductor
PostPosted: Thu Nov 28, 2019 1:46 am 

Joined: Tue Nov 26, 2019 6:36 am
Posts: 5
Hello Jim,

thanks for the reply.

Please check the attached picture.
In this situation i have a busbar along all SWB with a GAp of 111 mm between buses and also have electrodes with gap of 50mm in the connection to the protection unit, in this case the incomer from the source.

All the cubicles can be open in all the switchboard with live bus.

In this situation what should be the Gap to be used, 111 mm or 50 mm? With this question i am considering that a arc can exist anywhere in the SWB, in the main bus or in the electrodes that go to theprotection unit.


Thanks,


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 Post subject: Re: IEEE 1584 -2018 - Gaps Between Conductor
PostPosted: Fri Nov 29, 2019 8:03 am 
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A prudent engineering practice would be to consider the worst case. i.e. review different gaps and select the one that provides the worst case answer.

Since the bus gap affects the arcing short circuit current, it will also require close evaluation of the protective device's time-current characteristic.

Hope this helps.


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 Post subject: Re: IEEE 1584 -2018 - Gaps Between Conductor
PostPosted: Sun Dec 01, 2019 11:30 pm 

Joined: Tue Nov 26, 2019 6:36 am
Posts: 5
Hello Jim,

Thank you for feedback.

yes, i am also considering the protective device tripping time.
This project follows IEC construction and starting to see some big differences between IEC and the North American standard for the switchboard construction. I am measuring very small working distances and big electrodes gaps (for several reasons here)
What standard does the North American industry follows for the Switchboard construction?

Once again, thanks for you support.

Fluffy Bunny Feet


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 Post subject: Re: IEEE 1584 -2018 - Gaps Between Conductor
PostPosted: Mon Dec 02, 2019 8:55 am 

Joined: Tue Oct 29, 2019 6:23 am
Posts: 19
Gap, to me is a HUGE issue. In my "opinion" the common practice of defaulting to the gaps in the tables within 1584 documents is not a good practice! Those suggestions are often incorrect.

However, in the new 1584-2018 there is a very important aspect of AF calculations that is clear... if in doubt, use a bigger gap! So when you look at an enclosure or volume, and you see multiple gaps, use the one you know will host the arc... and if you know which one that is beyond a shadow of a doubt let the rest of us know! My guess is that the arc could be in multiple locations in most equipment and due to various factors it may be hard to predict. Most equipment geometries are more complex than the box & electrode configurations used in the collaboration's test protocols.

So, my advice it to use the largest gap in the space that "could" host the arc. That will give you the lowest arcing current and the most energy per unit time. I.e. it is conservative for both! If you guess to long but set the protection appropriately for it you may have over-calculated Ei by a calorie or two. If you guess to low for the arc gap, you may get a lower arcing current in the real event, then have your protection may not operate as fast as expected and your calculated Ei could be under-calculated by tens of calories!

Any value you use may be incorrect... the key is to bias it so the resultant error is more acceptable... For gap bias to a larger gap, for Ibf bias to a range of both low and high, for a box... if it is way too large, you may want to calculate Iarc as open and set protection accordingly, then recalculate as enclosed to get Ei. Generally do not use 24" unless you "know" that is the working distance, rarely is. Etc. a lot of human inputs into this calculation and it is not exact to the 3rd decimal palce, bound to be errors... they just need to be acceptable errors!


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