Seismic Rating of Electrical Equipment

[dpc]

I'm curious about how others working in high seismic risk areas are specifying electrical equipment for typical utility or industrial use.

Do you require equipment to merely survive the seismic forces or to actually stay in service?

What type of response do you get from equipment suppliers?

Thanks,

dpc

 

[buzzp]

For a former employer we used to test our stuff to some IEC standards for shock and vibration. This was the IEC 60068 series. IEC 60068-2-6 was for vibration and IEC 60068-2-27? was for shock. It seems these would be relevant tests for your particular application. These tests are common for testing products for sale in the European Union (not required though?). Hope this helps some. Buzzp

 

[dpc]

Thanks buzzp.

I know that Cutler-Hammer has done quite a bit of testing on a shaker table for a lot of their equipment. But for many types of high voltage substation equipment, we find that no manufacturer (in U.S.) has done any actual testing, probably due to the cost. They routinely take exception to any seismic requirements.

dpc

 

[willybuot]

Siemens has an excellent testing facility in Berlin that can simulate severe earthquake. We have visited their testing facility but they will only test the high voltage circuit breakers upon request by the equipment vendor since the equipment under test will no longer be used. Usually, the equipment seismic rating is 0.4G.

 

[buzzp]

That makes sense to me dpc. I imagine shaking something around that weighs several thousand pounds would be interesting and time consuming.
A rating of 0.4 G's is not much. Is this a sustained force over some period of time or is it a short duration?

 

[behdad]

IEEE 693 deals with Seismic requirements

 

[BJC]

Response from equipment vendors has been excellant. IF you specify the seismic zone that your in they can certify that their equipment will meet that criteria. That is IF YOU INSTALL IT PER THEIR INSTRUCTIONS. Be sure to get their drawings and instructions for installation and follow them. You may have to document the installation to satisfy the local building inspector.

I have had more trouble with conduit and tray installation than with equipment. Conduit and tray are typically installed without design drawings and it is harder to certify the installation will meet the seismic installation criteria. Be
B-Line, Unistrut and other strut manufactures have installation details that cover many situations. Some of the more complex installations ( like a rack of 10 plus conduits or two or three cable trays ) are not covered in the "cookbook" details. In some cases we have used a structural engineer to design or review design of "as built" hangers.
You may have to go into more detail for the installation of hangers such as numbering them and making detailed drawings of them( so you can document design and installation). Building codes require that some fasteners require witnessing to assure that they were torqued correctly. In short it may require you do business in ways you havn't done before.
If your in a seimic zone that requires an installation to meet a prescribed criteria it's better, cheaper and faster to plan on it from the start rather that later. I've seen it done both ways.

 

[dpc]

Thanks for the comments. Our experience has not been quite as positive. For many types of equipment (voltage regulators, reclosers), all manufacturers took exception to seismic requirements. In some cases they provided some details on the mounting, but this is only part of the equation. Another concern is the ability of the equipment itself to withstand these forces.

ANSI C37.81 was developed for nuclear applications and is quite severe.

The UBC requirements were intended to be applied to structures and not equipment, so there are sometimes conflicts.

My understanding is that UBC Zone 4 specifies an acceleration of 0.75g. The California BC Zone 4 requirement is 1.75g. Cutler-Hammer claims to have tested their gear to 2.0g. I believe ANSI C37.81 is higher than this.

As far as I know, not many manufacturers are doing any testing. It would be difficult for a large device such as a substation transformer. But switches and regulators could be tested if there was sufficient demand.

 

[cuky2000]

There are several high voltage power equipment and components manufactured by USA and foreign companies that had been seismically tested, qualified and approved to be used in high seismic risk zones such as BPA, LAWPD in the West coast.

There is practical limitation on the shake-table size, weight, displacement, velocity and acceleration of the to test large and heavy power equipment such as power transformers, reactors, capacitor banks, complex structures, etc. In those cases, combination of static, dynamic and time history shake-table test could be acceptable to seismic qualify power equipment in accordance with IEEE Std 693-1997.

Equipment mounted in high structure could experience heavier vibration than those tested at ground elevation. Anchoring method, foundation, soil type, equipment mounting, structure type, cable, loading combination, should be considered to qualify the seismic performance of the assembly.

Caution is advice went compare foreign equipment tested based only in the acceleration parameter such as 0.5g. There are in the US qualification and performance levels (high, moderate and low) base on vibration spectrum consideration that should be taken in account to be in compliance with the latest seismic requirement of IEEE and supplementary building codes.

 

[stevenal]

According to IEEE C57.114-1990,(now withdrawn) zone 4 = 0.5g. Did this change? We have specified and installed transformers to this standard. We have also specified the "definite purpose" (0.5g) breakers per NEMA SG4-1990, but they have dropped that category in the 2000 standard, simply referencing IEEE 693. In any case, we specify a minimum of zone 3, 0.4g on transformers, breakers, circuit switchers, switches, battery racks and relay racks. In most cases manufacturers do not have a zone 3 rated product, and deliver zone 4 instead. Haven't had a good test yet, luckily. I haven't really figured out how this all translates to the low, moderate, and high categories of IEEE 693.