LV Transformer arc flash labeling

[alehman]

Using SKM Powertools for arc flash studies and labeling, I've been wondering if there is a better way to handle LV transformers where there are multiple buses in a single enclosure. I usually print separate labels for each bus, which was the suggestion of SKM's technical support. It bothers me to have multiple labels because it is somewhat open to interpretation by potential workers which bus is being worked on. I would feel more comfortable with a single "worst case" label for such equipment. SKM can print labels with line-side and bus data for main-breaker equipment, but I haven't found a way to do this for transformers. Just wondering how others have handled this.

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[wbd]

If I understand it right you have a main bus breaker and then feeder breakers off of the bus that the main is protecting. Depending on the internal configuration (ie what is the probability of an arc flash starting in the bus work and engulfing the main breaker thereby rendering it useless.
I will label the main breaker with the AFH there and then a label for the other part of the swgr/swbd which is on the line side of the breaker. There would be two labels then.

 

[alehman]

wbd,
Thanks for the response. Actually this is a low-voltage dry-type transformer with the primary and secondary terminals in the same enclosure. Primary and secondary overcurrent protective devices are located remotely.


Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[DistCoop]

In a case like this, I would do a worst case scenario. I don't know if SKM has this ability automated. I determine the energy on the primary and secondary. You can open the properties tab on a bus and uncheck three boxes... something like "determine arc flash energy" or "display ac flash energy."

 

[dpc]

I would label it for the greater of the two incident energies.

 

[alehman]

In SKM you can create a table for "custom" labels to be included in the project, but it still calculates the incident energy and arc flash boundary based on manually input voltage, fault current, and arc duration.

The labels include bus voltage to warn of shock hazard and required glove class. I would want this to show the high-side voltage. I suppose I could use the custom table by entering the high side voltage and manipulating the fault current and arc duration to obtain the incident energy value it calculates for the worst case (low-side) terminals.

Considering the number of transformers on some of my projects, that is more manual manipulation than I was hoping to have to do. This gets especially messy when we have multiple system scenarios to evaluate. But the only alternative I see is to create completely custom labels for each transformer.

In the past I've just printed two labels, but I don't like that approach. I was hoping someone else had come up with a solution for what seems like a very common situation.

Thanks,

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[wbd]

So, it sounds like you are trying to label the transformer terminal compartment. From what I have seen this is not a normal practice, as NFPA 70E only requires that electrical equipment likely to require examination, adjustment, servicing or maintenance while energized be labeled. Examples are switchboards, panelboards and MCCs. Seems like a dry type transformer does not fall into this category. Is there something special about this installation?

 

[alehman]

Yes, the client is asking for the transformers to be labeled.

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[wbd]

I would label it for the greatest incident energy which would be the secondary side as the clearing device would be the primary side protection. That would give you worst case arc flash and then use the primary voltage for worst case shock hazard. That would give you worst case for both arc flash and shock hazards.

 

[PHovnanian]

alehman

I'd find the worst case for each terminal compartment. The object of arc flash labeling is to warn workers of the worst possible case they are likely to encounter when working in the area. If there are multiple busses in one compartment, even though the work might be confined to one of them, there's a possibility that an arc could involve any other in the area.

Like working on the primary terminals and dropping the wrench across the secondaries.

 

[alehman]

Thanks guys. I agree with the consensus about using the worst case.

My original question was how to make the SKM software create these worst case labels somewhat automatically. I have systems with a lot of these transformers and would prefer not to do the calculations manually for every one.

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[recs]

I only affix one worst case label to a transformer.

I model the transformer with a bus at the primary and a bus at the secondary (i.e. TR-1-P and TR-1-S).

I then run the arc flash and these two locations will be together and easy to compare which is the worst case.

When I print the labels I only print the case with the worst AFIE.

 

[LionelHutz]

I don't see why you'd have to manually calculate anything. Worst case, you have to pick the high side voltage and low side arc data from the results and manually create a label from that. I don't use SKM so I have no idea if you can manually change any of this data in that software.

 

[alehman]

SKM doesn't allow you to manually edit the contents of the labels. They are printed based only on values calculated by the software. I was just hoping to find an SKM user who might have found a work-around. It allows you to build a table for "custom labels", but it still calculates the incident energy and HRC and boundary based on arcing time and fault current that you have to enter manually.

The best method I've found so far is:
1. Run the calculations normally, with buses assigned at the primary and secondary terminals.
2. Create a custom label table.
3. Manually create a table entry for the transformer.
4. Enter the high-side voltage.
5. Enter bolted fault current for the terminals with the worst-case incident energy from the original calculations.
6. Enter a total arcing time and then adjust it up or down as needed in order for the incident energy it calculates to match the worst-case from the original calculations (this is an iterative process).
7. Repeat 3-6 for each transformer.


Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[LionelHutz]

That sounds like a pain. Etap isn't much different because I don't see how to manually change the voltage hazard but it does give the arc current and clearing time when you look at a bus and it will produce a table of the data. Can you get a table of the data from SKM? Maybe you could create a label form in Word. Modify the table to put the proper data in for the tranformers and then do a "mail merge" type of thing to print the labels.