What is the purpose of anchoring a transformer that weighs 15,000lbs? 2

[bdn2004]

I look at the work we are performing and just wonder why do we have to anchor such a big heavy piece of equipment?
Do utilities anchor transformers to their concrete pads?

 

[davidbeach]

Earthquakes are very good at moving heavy objects.

 

[dpc]

Do utilities anchor transformers to their concrete pads

Not always done in times of old, but it is generally a requirement today due to seismic concerns, as David pointed out.

 

[bdn2004]

Actually the point of my question is that we've anchored many transformers down on a concrete pads. Our Client, has found in the manufacture's literature that the transformers should be anchored a specific way.

We had a reason we did what we did, as the concrete pad wasn't wide enough to do it as it was shown. So you guys are saying an earthquake force comes along, enough force on its own could move a 15,000 dead weight...and those anchor bolts are going to hold that down?

I'd like to know how they determine the size, strength and where those bolts gotta be placed in order really know that.

It all comes down to money, such a trivial thing will end up costing $1000s to fix. It always does.

 

[zeusfaber]

This reminds me a bit of the contractor who thought that, because my Main Battle Tank weighed just shy of 65 Tonnes, there was no point in lashing it onto the low loader. The subsequent picture made page 7 of the Sun.

A.

 

[Skogsgurra]

I had a problem understanding what you needed a Main Battle Tank for. Then I saw the (Military) after your nick. Never thought of that before.

OK that bolts could help ride through a mild earthquake. But the tougher ones?

OP: What are the typical magnitudes of your earthquakes? Ours are 1. mostly absent and 2. infrequent and 3. below 2 on the Richter scale. We had one around 30 years ago. Then I thought it was the neighbour's wife that hit the barn door (outhouse, 50 m away) with the tractor again.

If you are in a similarly geologically quiet zone, you may get away with the installation as-is.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[dpc]

Yes, that is what we are saying. The design engineer will specify a particular seismic zone and that determines the horizontal and vertical forces that the transformer must withstand. The civil engineer designs a pad with sufficient mass and reinforcing and the transformer designer determines an anchoring system that will withstand the specified forces. If you install it per the manufacturer's specs and it fails, then shame on him. If you do it your way and it fails, guess who is to blame? Seismic forces can destroy structures that are orders of magnitude more massive than a transformer. It seems trivial until the earthquake happens.

http://www.iitk.ac.in/nicee/wcee/article/13_1605.pdf

http://www.asce.org/uploadedFiles/I...ner_2011_Power_Transmission_Systems_TLCEE.pdf

 

[racookpe1978]

After the earthquake, the power company is going to want to use that transformer immediately ... NOT wait 6 months for a replacement to arrive..

 

[bdn2004]

I read an article on line that said the strongest earthquake ever in this area was 3.4 the Richter scale. I lived through a 5.4 a few years ago and can honestly say that I didn't have to move even my 10 lb coat rack back into place or my 200 lb couch.
Again we did anchor these transformers firmly to the concrete, but we went through some other tabs on the base that we were told are there to attach the transformer to shipping pallets. we will end up changing it I'm sure and eat all the costs. 15000 lbs in a footprint of about 3' x 7' oh and about 21 huge underground primary and secondary feeders are attached to this thing...I'm still having a hard time believing this.

 

[prc]

Definitely it is better to anchor the base of transformer to foundation esp in earthquake prone areas. It is not a good practice to leave alone as the tank base can slide even under slight tremors.

The standards for Seismic design of Transformers are covered in the following:

IEEE Standard 693-2005 Recommended Guide for design of substation
IEEE Standard C57.114-1990 Seismic Guide for Transformers &Reactors (withdrawn in 1996)
IEC TS 61463 -2000- Bushing seismic Qualifications
IEEE Standard 1527 –2006 Recommended Practice for the design of flexible bus work in seismically active areas.

The above standards do cover about anchoring:
Quote
4.2 Foundations. The transformer and all interconnected equipment should be placed on a monolithic foundation so as to reduce differential movement due to the design earthquake. Provision should be made to accommodate expected differential motions between equipment mounted on separate foundations but which are interconnected. Provision should also be made for interconnected equipment mounted on the same foundation but having differing frequency content. Lastly, consideration should be given to the interaction of underground conduits and the foundations. Foundations should withstand all forces resulting from the design earthquake in the vertical and horizontal directions simultaneously. A comprehensive soil survey is recommended to determine if any unusual conditions exist at the site that would warrant special design considerations for the foundations.
4.3 Anchoring. It is recommended that transformers be anchored by welding the base to structural steel members embedded in or firmly anchored to a concrete foundation. Size, location, and type of welds should be shown on the manufacturer’s drawings. All welds must conform to applicable AWS specifications. AISC weld allowables should be used. However, the one-third increase in weld allowable stress due to earthquake loads should not be permitted. If bolts are to be used, size, strength, location, and materials should be shown on the manufacturer’s drawings. The size and strength of the anchor bolts should be determined by bolt material allowable stresses. However, the one-third increase in bolt allowable stresses due to earthquake loads should not be permitted. It is recommended that mild ductile steel, such as A36 or A307, be used, and that design philosophy such as stated in the article, “Design of Threaded Anchor Bolts” by John G. Shipp and Edward R. Harringer, Engineering Journal, AISC, in the second quarter of 1983, be followed. The length of embedment and the type of bonding to that portion of the anchor system within the foundation should be determined by the user and should be greater than the strength of the bolts attaching the equipment to the foundation. Consideration should be given by the user to any unequal distribution of dynamic earthquake loadings on the anchor bolts. All anchor systems must withstand the forces resulting from the design earthquake. (from 1990 IEEE standard)
UNQUOTE

As you can see there are two practices –weld the base of transformer to the anchored plate on foundation (popular in US) or use M24 or M36 Foundation bolts on either (longer) sides of transformer. Bolts are taken from the roller frames mounted on rails on foundation.(one or two bolts from each frame). This is found popular in Japan (where they experience maximum number of minor tremors)and also followed in India.

Another point to remember is higher the load, less g it can tolerate!

 

[crshears]

Once saw an oil-filled 115 kV circuit breaker rip itself clean off its concrete pad, shearing all its'hold-down' bolts in the process, due to the mechanical forces generated during a relatively close-in slow-clearing electrical fault. Miracle the tank wasn't ruptured...

Reason enough?

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[bdn2004]

Crshears,
Is there anything in any standard that requires anchoring a transformer for the express purpose of keeping it intact during a fault? It's much more likely than a 8.0 earthquake yet I don't recall ever seeing anything like that.

As I pointed out, an earthquake would be an extreme rarity. I used to work for a chemical company that has and still does have on every drawing "Minimum Essential design is the requirement" and is the company policy. And another thing they had in their specs I always remember..."do not design for catastrophic failure". Doing either costs money. And money is not an unlimited resource. The money you spend unnecessarily could have been perhaps used for something much more beneficial. This won't be that big a deal but just thinking this way is what bothers me.

 

[davidbeach]

OK, your chemical company can go out of business following an earth quake that does too much damage, or ride on business interruption insurance until they can get their feet back on the ground. Do you want your local power company to take the same approach?

 

[racookpe1978]

You, an electric engineer working with power transformers, are trying to "argue the Code" (for structural earthquake standards in your particular area) because "the transformer is very heavy" ....

Don't do it.

In this case, the solution is simple, not actually very expensive in the big scheme of "providing power after an earthquake", and straightforward.
Look up the Code,
Understand the relevant parts of the Code,
and, finally, Follow the Code.

 

[bdn2004]

This is maybe the most successful chemical company in world history. They didn't say do bad engineering.. They said do what is required no more no less. That approach is exactly why they are successful.
A power company or a chemical company would probably be criminally negligent if they didn't design to seismic standards in San Francisco. I'm not arguing that.
This is a no risk seismic zone. But a generic detail is ruling the day and trumping a reasonable installation and changing it will just add cost to the project. The problem is this mentality doesn't just show itself once like here...it's all over the place. And America wonders why it can't compete.

 

[racookpe1978]

A few years ago, a quake south of Memphis rattled houses as far north as Chicago.

A quake in Charleston broke chimneys across the Atlantic seaboard.

We were woken up by an earthquake across the border in Alabama from a quake that was felt over in South Carolina.

A nuke power plant in Virginia was shutdown by a quake there.

There is an active fault down the St Lawrence River bed with regular earthquakes.

Where do you think is a non-seismic zone in the US?

 

[bdn2004]

I concede I don't have all of the seismic data memorized for the USA.
Where these transformers are anchored in 4 places are within 6" of where the mfg says to anchor, through the same gauge steel at the 4 corners.
The pads were not designed or installed by us and the underground conduits were not installed perfectly. The pad left maybe 5" on each side in the long direction - not much. In order to get the transformer to fit over the duct banks it had to encroach on this 5" leaving even less room and no room to anchor as per the mfg detail. And that's how things are in construction.
So what would you do? I guess we could have them remove the xfmrs, bust out all the duct bank, send it back to engineering and have them redesign the pads and bust all them out too. we must get it exactly per a generic detail to plan for an earthquake that hasn't ever happened because those anchors will save the day.
Or perhaps we could stand back a say what do these anchors really do? And will it really make any difference if they were moved slightly? Call me crazy.

 

[rterickson]

Have you considered asking your structural engineer to:

1) Evaluate the manufacturer's design;
2) Evaluate your as-installed design; and
3) If the former is superior to the latter, engineer the difference?

 

[LionelHutz]

I'm confused. You seem concerned with the financial burden you (your company) will shoulder by fixing the installation yet you are posting that you were not responsible for the engineering or installation of the transformer base. So, why would you have any financial responsibility to fix it? Take a technical response back to the owner explaining how the pad is bad and won't accept the proper anchoring and make the person who improperly installed the pad responsible for the expense of fixing it.

 

[davidbeach]

Yeah, that, what Lionel said.