Substation Structural Design 3

[WARose]

My arm has been twisted into doing a electrical substation for a client. Never done one. Have done a few transformer bases.....but that's been a while. After reviewing what I can (including old threads here), I have a few philosophical questions. I will put the question itself in bold....so to separate the wheat from the chaff. I would appreciate responses from experienced substation structural design engineers.....although some of this may have to be answered by a electrical guy/gal.

1. I am (highly) confused as to what codes are to be used for this. ASCE has a MOP: ASCE 113. And it has some good info. But it's load factors are different than current IBC codes. IEEE has the code for seismic design: 693-2018. IBC doesn't reference either of those documents in the version I use. So what code(s) do I use for this? Is it a matter of: I'd take a run at it with ASCE/IBC.....and if those other codes give something more conservative.....then run with them?

2. Is it common to have a lot of equipment up on pedestals....but everything just one one mat.....or individual footings?

3. What kind of vibration issues can I expect with this? I remember transformers have some unbalanced forces (especially because of the associated pumps and so on). Anything else? Ballpark, what kind of frequencies & unbalanced forces are we talking here?

4. At least with some of this equipment, I've seen containment for possible leaks. Is common practice to contain the whole area?

5. What kind of fire protection is needed for some of this stuff? This subject is one of the few times this kind of equipment is specifically mentioned in the IBC. Apparently some transformers need fire walls near other stuff....what else?

I may have a few more questions as I think of them......thanks in advance.

 

[dauwerda]

NFPA 850 is specifically for generation plants and DC converter stations - it is not applied to typical substations in my experience. Check out IEEE 979, "Guide for substation fire protection".

I have never seen any requirements or designs for blast explosion.

Yes, transformers are the main items to be worried about as they contain large amounts of oil. Older breakers were also oil filled but if this is a new installation I would not expect to see an oil breaker.

Metal Clad switchgear is also susceptible to large arc flash explosive type failures.

 

[WARose]

Thanks again dauwerda.

 

[miningman]

For mining purposes, The most usefull Canadian document is the federal document " Use of electricity in Canadian mines". It probably isnt directly identified but when we design underground sub stations we always try to ensure that in the event of an explosion , anyone in the sub station has immediate and direct access to the door / access to the outside area.

 

[dauwerda]

Glad I can help.
One other document you may find useful is IEEE 980, "Guide for Containment and Control of Oil Spills in Substations."

 

[DayRooster]

Be careful because some substations due fall within NFPA 850. Need to talk to the utility or electrical to understand the design criteria. Also we always found a way around blast requirements. We even went as far as to call the walls “fire walls” and not “blast walls” so there was no confusion. Even though our walls would still be like 18” thick for some of the bigger transformers.

As for blast design that is a real thing depending upon the design requirements. The person that brought it up mentioned petrochemical plants. It would likely be a requirement there since you can have consecutive blasts if you don’t protect against the first one.

I recommend asking for all the specific fire protection requirements that you need to follow then reading them line by line. That’s what we would do.

Also on a related note, check out this video of transformer fires:

https://youtu.be/D8EQPx-ptKk

You will notice how the fire goes for a while before it blows. Also they only get bigger as it counts down.

Also, I should note that there are special transformer oil blends out there that don’t require as much fire protection. Also if it’s air cooled then that’s not a problem either.

 

[WARose]

@dauwerda and/or DayRooster.....question for you: what kind of budgets are you use to seeing for Structural for substations? I know that's very general (since no 2 are exactly alike), so maybe you could break it out in hours per piece of equipment or something. In any case, it's nothing that cannot wait until Monday.....thanks again for your assistance.

 

[oldrunner]

I suggest that you contact Burns and McDonnell to assist you in this endeavor. It will save a lot of time for all. A new ASCE 113 manual will be published possibly next year. It has been expanded tremendously and addresses many of the questions that you have asked. IEEE 693-18 has much material - especially some excellent recommendations on foundations. If you are in a seismic area, you should be using this. Use ASCE 7 thermal movement requirements for the transformer foundation anchorage. A TVA manual on steel thermal movements is also available. There are two additional loads for transformers that are sometimes not considered - steel in the sun (solar) and operational temperature compared to the original ambient temperature. ASCE 96 is also a good reference. Talks about some transformers anchorage that has been welded to embeds in the slab being compromised by concrete "shrinkage". Think solar heating and a mismatch of the steel and concrete COTEs. Because one doesn't know the COTE of the concrete, best to design like any horizontal tank - one end anchored and the other end guided. I have submitted a new description of large power transformers to be included in ASCE 7-22 where the description of transformers is revised from "rugged" to "fragile" after a number of years because of insulation degradation in the coil windings. No one talks about the end of life of a transformer, but consider that it is very difficult to determine when a transformer should be removed from service. If the customers business model is "run to failure", then the transformer would just stop one day or catch fire and blow up. Note that transformers are not machines but a special animal.

 

[WARose]

I suggest that you contact Burns and McDonnell to assist you in this endeavor.

That's out of the question (i.e. contacting a 3rd party, and I wouldn't contact them for anything even if I did). But I appreciate your input.

 

[dik]

From Project Notes

A-FRAME DESIGN

A-FRAME SUPPLIER IS RESPONSIBLE TO DESIGN AND TO PROVIDE A STRUCTURE THAT IS SUFFICIENT TO ACCOMMODATE THE EQUIPMENT SHOWN IN THE CONSTRUCTION DOCUMENTS AND IN THE MATERIAL DATA LISTS

A-FRAME SUPPLIER TO PROVIDE SEALED DESIGN CALCULATIONS ON REQUEST

A-FRAME TO BE PROVIDED BY SLACAN INDUSTRIES INC. OR AN APPD ALT. DRAWINGS SHALL BEAR THE SEAL AND C OF A FOR THE PROVINCE IN WHICH THE PROJECT IS LOCATED

EQUIPMENT SHALL BE DESIGNED TO PROVIDE CONTINUOUS LONG TERM SERVICE

PROVIDE LIFTING LUGS, ETC. TO SAFELY INSTALL A-FRAME. PROVIDE CADWELD CONNECTORS, GROUNDING LUGS OR PADS AS REQUIRED TO MAINTAIN ELECTRICAL CONTINUITY WITH GROUNDING GRID

A-FRAME TO BE DESIGNED IN ACCORD WITH CSA S16 FOR ALL LOADINGS PRESCRIBED BY THE MBC. THIS INCLUDES DEAD AND LIVE LOADING, WIND LOADING, ICE LOADING AND SEISMIC LOADING AS REQ'D

A-FRAME TO BE DESIGNED FOR ICE LOADING STIPULATED IN THE CONSTRUCTION DOCUMENTS. LOADING TO BE CONSIDERED AS LIVE LOADING

A-FRAME TO BE DESIGNED FOR ALL ELECTRICAL EQUIPMENT STIPULATED IN THE CONSTRUCTION DOCUMENTS OR ON MATERIAL DATA SHEETS. LOADING TO BE CONSIDERED AS LIVE LOADING

WHERE ELECTRICAL EQUIPMENT WEIGHTS ARE SHOWN, CONTRACTOR SHALL VERIFY ALL LOADS PRIOR TO FABRICATION

A-FRAME SUPPLIER SHALL VERIFY LOCATIONS OF ALL EQUIPMENT AND FASTENERS. IF REQ'D EQUIPMENT IS NOT SHOWN IN THE CONSTRUCTION DOCUMENTS, SUPPLIER SHALL ADVISE CONTRACT ADMINISTRATOR

PROVIDE FASTENERS THAT WILL NOT PROMOTE GALVANIC CORROSION

Slacan provided A-Frame structures for half a dozen projects I worked on. I'll see if I can dig it up, but I also have a spreadsheet for A-Frame design somewhere; I don't think I left it behind. I do all my programming on my own time, and not billable, to retain ownership (not necessarily true, but close).

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dauwerda]

For what its worth, the large utility I used to work at did not anchor transformers to foundations at all - all of their service territory was also in low seismic areas.

I'm afraid I'm not much help on the budget. I have used 8 hours each for the simple stuff (single and 3-phase bus supports, CCVT supports, etc.) and anywhere from 16-40 hours for the more complicated multi-bay box structures.

 

[dik]

I don't recall what the outcome was, but I had spec'd the large transformers on the one project to be anchored in accordance with the product data sheet; I don't think they were anchored. Non seismic and massive; they weren't going anywhere.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[ukengineer58]

if you have a substation with switchgear etc in it you may have strict deflection criteria. To much deflection the switchgear faults off. Thats a issue we had to deal with on a suspended floor substation once.

 

[DayRooster]

WARose - Budget can verify quite a bit but it’s generally pretty tight. Most substation structural engineers often do the civil site too. That adds a bit to the hours. Also if you do some steel structures or buildings then it can add to it too. Often there is more time in steel structure stand design than the footings. Otherwise as mentioned previously each equipment footing doesn’t have too many hours associated with it. The biggest would ever the transformer that can vary quite a bit based on size and design requirements. If it helps you visually, most equipment foundations can fit on one plan sheet with 1-2 Detail sheets to cover all. As an example, if I recall correctly I would see 8-24 hours for each general equipment footing and 32-80 for the transformers. Large dead end structures might get a bit more attention too (16-32). I am sure there are people that will say they have bid substation for less and others that will say they have bid for more. Again it all depends upon size and standard requirements.

Also, last I checked Burns and Mc is not the only outfit in town. As mentioned in non-seismic areas transformers are generally not anchored. Because they are so heavy that the friction force is through the quite a bit. In seismic areas you generally consult with the transformer vendor. There are designs that allow for thermal movement and also design for seismic. Most often the equipment vendor has to account for this in their sole plate while you just place the anchor diameter called out and size embedment. Burns and Mc is not the only company with the secret sauce. As for the other thermal affects - just account for them. Most programs nowadays can add a thermal load to your load cases…

Edit: we would also hold our drilled pier settlement and top lateral deflection values pretty tight. If I recall we would run L-pile and hold to at least 1/4 inch at the top (in most cases). And vertical settlement was 1” or less. I’m trying to remember but I think specific items like the switches required even tighter settlement criteria. Can’t recall exactly but yes deflection is critical to keeping everything operational.

 

[WARose]

Thanks again DayRooster!

 

[Agent666]

Been many years (20) since I was involved in some substation design work.

One thing that I don't think has been mentioned in skimming through others replies is that disconnectors (I think they were called this, like I said 20 years ago, so exact details are hazy) had some moving arms/bits that swing into place very quickly to turn on/off/switch the electricity. They had some reasonable lateral loads associated with this action that needed to be considered in the structural design of the cantilevered posts they were attached to. These loads came from the electrical people based on the equipment specified. I recall they did some calculations to come up with the loads.

So, make sure you nail down any additional operational loads with the power engineers working on the project.

Another tip is if you need to bolt down the transformer, we used to cast in the bolts for all connection points attached to a welded steel frame incorporating all the bolts. This frame was set in place below the pad footing in a separate pour so that the alignment of the bolts was perfect. Suppliers of transformers do not take kindly to you chopping up the baseplates till it fits! The cage for the footing was then setup around the bolts.

https://engineervsheep.com

 

[DayRooster]

Yes Agent is correct that you need loads from the vendor and/or electrical engineers. If you don’t get these specific loads are are concerned then you can always consult IEEE. A long time ago I read the relevant standards to make sure I was fully up to speed with what to ask for.

Btw, disconnect switches are cool…

https://youtu.be/GMbN9nb3qyk

 

[dik]

I used to develop a 'Load Matrix' outlining the equipment, weights and locations.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik