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Associate

Join Date: Oct 2010
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Fault Levels

10/24/2017 11:30 PM

I am working in power station where the switchyard was built in 1977. Due to expanding network the new fault level calculated over the next few years is 63 kA(old 30 kA). We have started replacement of equipment like breakers,disconnect,lightning arrestors etc. The question is do we need to replace the concrete foundations for these equipment. The old one in my opinion(since Air blast circuit breakers were installed) will with stand the new equipment(SF6 breakers being much lighter). Does fault levels have direct affect on foundations.

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Guru

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#1

Re: Fault Levels

10/25/2017 11:10 AM

I would at least have a structural engineer sign off on it....the concrete may have degraded, it may need to be tested...

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Guru

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#2

Re: Fault Levels

10/25/2017 4:01 PM

The concrete is there to support the weight of the equipment.

My opinion is that it is

You might look for a civil engineering forum and ask them for some free advice on this.

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Guru
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#3

Re: Fault Levels

10/25/2017 4:49 PM

Fault withstand capability of switchgear is not dependent upon the strength of the anchoring system. SEISMIC withstand ratings are.

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Guru

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#10
In reply to #3

Re: Fault Levels

10/26/2017 1:54 PM

The mechanical forces caused by an electrical fault (especially at 63kA level) will put significant stress on the electrical equipment, its supporting structures, and its foundations. Part of the switchgear or equipment's fault withstand capability depends on how it is supported and secured. If you've ever seen a slow-motion recording of the movement of a 3-phase bus during a fault, you know what that's like - it can looks like galloping waves whipping the bus around, or Superman bending steel bars. I agree with some of the other responders that the OP needs to have a qualified civil/structural engineer look at the condition of the existing foundations as well as their design to see if they are adequate for the forces that could be exerted on them in a fault.

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Guru
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#4

Re: Fault Levels

10/25/2017 6:28 PM

You or someone should determine if the concrete is there just to support dead weight (in which case you are probably okay) versus participating in any bus bar bracing that is there to withstand magnetic forces generated by large faults.

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Associate

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#5

Re: Fault Levels

10/25/2017 11:22 PM

Ok thank you all. As fas as bus bar arrangement is concerned we have 220kV and 500kV bus bar interconnected through auto transformers.Breakers are in breaker and a half scheme. We are replacing the 220kV breakers,CT's,Disconnecctors and bus bar but the foundations have been checked and will be reused. For500kV lightning arrestors and CCVT are also being replaced.The problem is only the 500kV civil foundations..My opinion is it need not be replaced

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#6
In reply to #5

Re: Fault Levels

10/26/2017 12:27 AM

What grounds do you have for that conclusion?

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Associate

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#7

Re: Fault Levels

10/26/2017 12:42 AM

there is this old switchyard which we are upgrading.the foundation there is a square having 0.9 meter one side.we have built a new switchyard to add new generating units.the foundation there is 1 meter square.Physical condition of old foundation also good.No cracks. But will ask expert opinion of civil consultants.basically what I needed to know link between fault levels and foundation.ITS MORE IMPORTANT TO LOOK AT CONDITION OF FOUNDATION what I understand

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Guru

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#8
In reply to #7

Re: Fault Levels

10/26/2017 9:48 AM

One definition of the ampere is "that current in both conductors that produces a force of 2 X 10-7 Newtons per metre length with one meter spacing between straight parallel "infinite" length conductors in vacuum".

If you feed in numbers for 630002 amp & 4 metre spacing height you get 20 kg/metre, say 200 kg with 10m spacing between equipments retaining the conductors.

Will this worry you? Are breakers single pole separate units? You have 4 times the force you had with old equipment @ 30 kA. Also, you have reduced weight & reduced footprint distance between bolts with new plant but probably same height (between conductors & earth return), so more force required to resist rotation.

I reckon that you will find most equipment weighs more than 200 kg, so just gravity may keep it in place.

The forces will fluctuate at 100 Hz, so structural resonance is a hazard. However, the HV equipment designers will already have calculated and tested the forces with short circuit tests and tests to ensure an internal fault is contained - so have you asked them for their foundation requirements, particularly if any tension forces in bolts, so you can pass them to civil engineers?

As has been written by other posts, the most important factor is probably the condition of the concrete for new bolt holes and other risks, like earthquakes.

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Power-User

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#9

Re: Fault Levels

10/26/2017 12:10 PM

Electrical equipment foundations in switchyard are designed to withstand dynamic forces due to earth quakes as well as those experienced by the equipment during electrical faults.

Equipment vendors generally give us typical foundation details.

However, since the existing foundations are old, it is necessary to approach a civil engineering specialist for assessment.

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