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Irregular Bending of 500KV Tubular Bus

09/05/2019 6:44 AM

I am working in a power station recently commissioned.It has a 500KV switchyard which is an extension of the existing one.Now attached pictures show quality of installation.We are pressing on the contractor that the irregular bending of the bus bar is not onle aesthetically bad but also the bending will cause the thickness of the tube to be less at the bends effecting its current carrying capacity.Can any one has more points to add to Three pictures attached.New shows new switchyard while old shows existing or old one

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#1

Re: Irregular Bending of 500Kv tubular bus

09/05/2019 6:56 AM

It appears to me that the bend is an offset to compensate for different heights of the insulators between new and old.

Either the insulators are different heights,or the foundations were poured at the wrong level.

My best guess is the latter,considering the various offsets:

Known design outdoor switchgear 500 kV (Valleys A.P., Changin GF Outdoor switchgear with hard tires. M.: Energoatomizdat, 1988, p.68-74), the arrangement of which provides a rigid busbars only the lower tier (inside cells). For the upper tier, providing communication between cells, used flexible busbars. Rigid busbars of the lower tier is made tubes from aluminum alloy T diameter up to 150 mm with wall thickness of 10 mm Busbars are designed for dynamic effects in the short-circuit current (short-circuit current) up to 63 kA (effective value of a periodic component), static load from the speed of the wind for III climatic region and ice for the fourth district. The maximum deflection of the pipe bus is not more than 1/80 of the span.
https://russianpatents.com/patent/231/2310260.html
© RussianPatents.com - patent search, 2012-2019

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#2
In reply to #1

Re: Irregular Bending of 500Kv tubular bus

09/05/2019 6:58 AM

Yes but what are the technical flaws.Contractor says it is working

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#10
In reply to #2

Re: Irregular Bending of 500Kv tubular bus

09/05/2019 10:07 AM

In a non-blame culture, what is important is who does what to put things right.

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#15
In reply to #2

Re: Irregular Bending of 500Kv tubular bus

09/05/2019 11:06 PM

If it’s working do you have access to a thermal camera to check for elevated temperature at the bends , or a laser , non contact type of thermometer to enable temp measurement from a safe distance while also comparing resistance losses ?

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#18
In reply to #15

Re: Irregular Bending of 500Kv tubular bus

09/06/2019 8:03 AM

The aluminum conductors conduct heat very well,and it is unlikely to show a hot spot.

At 500kv,the mechanical stresses can be extremely high in the event of a short circuit condition.The tubing should be designed to survive these stresses as well as carry the rated current.

Corona effect is also a concern if the bends are too sharp.

I would hope that the bends are custom designed and manufactured to meet all engineering specifications,and were provided to the installing contractor already bent.

If this was on site Ad-Hoc bending,beware!

A contractor qualified to work on this type structure will not take chances by installing anything out of spec because of the immense liability,and his insurance bonding company may not pay for damages due to improper installation.

As stated by others,refer to the original design specs to verify the origins of the bends.

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#3
In reply to #1

Re: Irregular Bending of 500Kv tubular bus

09/05/2019 7:03 AM

and secondly the offset is not between old and new.Its bewteen new disconnector and new Ct or new disconnector and new breaker

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#8
In reply to #3

Re: Irregular Bending of 500Kv tubular bus

09/05/2019 7:31 AM

It it still goes back to a difference in heights of the two connections,for whatever reason.

Careful measurement of the equipment and foundations will reveal the source of the mismatch.

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#4

Re: Irregular Bending of 500Kv tubular bus

09/05/2019 7:04 AM

What does the maker of the tubular bus bar have to say?

...as for irregular bending? No good.

It should be uniform.

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#5

Re: Irregular Bending of 500Kv tubular bus

09/05/2019 7:07 AM
  • If the conductor is sized such that the introduction of a modest bend would affect the current-carrying capacity, then there is no safety margin and it is therefore undersized.
  • If it is working satisfactorily and has been stressed-tested to the limits of the virtual design envelope during commissioning then the bend is of no consequence other than aesthetics. This is an electrical switchyard and not a public work of art.
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#6
In reply to #5

Re: Irregular Bending of 500Kv tubular bus

09/05/2019 7:25 AM

Aesthetics will matter.Why then we have to align all equipment.They can be installed haphazardly

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#9
In reply to #6

Re: Irregular Bending of 500Kv tubular bus

09/05/2019 7:38 AM

It sounds like these things weren't considered at conceptual design.

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#7

Re: Irregular Bending of 500Kv tubular bus

09/05/2019 7:29 AM

The timing of the bending operation will also affect the strength of the bus.

It is recommended that bending be performed as soon as possible after the extruding process.

If it is not possible,the bus bars should be refrigerated to reduce the rate of age hardening.

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#11

Re: Irregular Bending of 500KV Tubular Bus

09/05/2019 11:33 AM

To my mind your concern over ampacity is likely over blown; the cross-sectional area of conductive material is not going to change significantly in a small offset like that.

But the more concerning thing thing to me is the mechanical issues at 500kV in a switchyard. Aluminum (if that’s what it is) must be annealed in order to achieve useable tensile strength as bus bar. Tensile strength is diminished when material is bent.

Does it “work” to carry current? Yes. Will it “work” to hold up under fault conditions now that the tensile strength is compromised? Unless the design was specifically tested WITH those offsets in it, you will not know until there is a fault on the system and then if it fails, it’s a big disaster. Can the installing contractor prove to you that the withstand capacity is equal to or greater than the available fault current in that switchyard? Probably not, but that’s the approach I would take with them. Force them to prove that it meets requirements and performance expectations rather than aesthetics or whether the current carrying capacity has changed.

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#14
In reply to #11

Re: Irregular Bending of 500KV Tubular Bus

09/05/2019 6:32 PM

A lot depends on the type of aluminum used.The 6000-T4 series aluminum will age harden over time.If bending is required,it should be done as quickly as possible after forming,or refrigerated to delay age hardening.

Here is a link with details:

https://mcwadeproductions.co.za/technical-info/https://mcwadeproductions.co.za/technical-info/

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#12

Re: Irregular Bending of 500KV Tubular Bus

09/05/2019 4:25 PM

While I am not an expert on the subject we actually design and build these for substations and I have a little bit of knowledge and access to our in-house design team here, so you may be in luck for some answers.

Before I go to them my understanding from the photos you have posted is that the existing substation already has busbar with sharp angle bends (the last photo in your original post) and your concern is not the fact that the busbar is angled like this but that the phases are not uniformly angled on the new busbars because the insulators are at different heights (second photo in your original post). Correct?

Normally (from my understanding) busbars are as straight as possible for a number of reasons and if the surface the busbar supports are built on cannot be flat then the height of the insulator support posts is adjusted to compensate at the design stage.

Any custom busbar shapes are agreed to at the design stage and carefully manufactured by the busbar supplier and supplied for installation on site without further modification necessary to get them to fit.

From the looks of it the designers knew there were going to be issues with flatness of the surface and designed in special custom-shaped busbars to accommodate the issue. You would have to look back and see what was originally agreed to in the design, because I would be very surprised if this change was not known about, agreed to before the busbars were manufactured.

If this is the case you are left with going back to the people that signed this design off and discussing with them.

If however and <cringe> the installer just bent the busbars on site to fit then you would need to go back to however authorised this and the original designers of the site and discuss with them if they think the new shape and quality of workmanship is acceptable. And if on site modification of the busbars by a contractor was even allowed or agreed to.

If this were my site and a contractor did this without authorisation they would be responsible for the cost of replacing the busbars they modified without approval.

So in short, find who actually approved the changes and discuss with them. Oh, and let us know what you find.

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#13

Re: Irregular Bending of 500KV Tubular Bus

09/05/2019 5:36 PM

In order to avoid cracking of the burs bars, a bending radius of 1 d (bar thickness) must not be undercut. The max. bending angle of bus bars will be 90°. If the bus bar is to be bent beyond this angle, bending will have to be done in two sections.

IEEE "Guide for Design of Substation Rigid Bus Structures"

Another source said that bent bus bars must be straightened before installation.

You will need to analyze your procurement and installation specifications.

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#16

Re: Irregular Bending of 500KV Tubular Bus

09/06/2019 12:56 AM

Thank you all for the replies.With all this I will be in a better position to tackle the issue

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#17

Re: Irregular Bending of 500KV Tubular Bus

09/06/2019 7:09 AM

Bending neatly to get levels right is one thing, but this seems to be 'ugly' bending to get the length right....and does it matter?

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#19

Re: Irregular Bending of 500KV Tubular Bus

09/06/2019 9:50 AM

I trained as a heavy current electrical engineer in the busbar department of one of the world's largest cable makers. As well as designing busbar systems I also have some experience of designing and specifying insulators.

When installing systems exposed to the weather, bending bus bars so that the bar approaches and leaves insulator posts horizontally is normal practice. In very cold weather it prevents rain water running down a inclined bar and compromising the lower insulator post with a build up of ice.

Providing all the bends are in the vertical plane it will have no effect on the forces generated during a short circuit.

The amount of work and age hardening is insignificant and comments on this topic constitute a red herring that should be ignored.

Post insulators are designed principally to withstand short circuit forces in the horizontal plane. Post insulators also fare better in compression than tension. Short circuits generate repulsion forces between the phases. So the phases are always aligned horizontally to match the maximum withstand characteristic of the insulators. That is why when vertical bends are introduced all three phases should mirror each other to keep the forces horizontal along the whole length of the bar. In your case, in the event of a short circuit, the misshaped lower outer bar would exert an upward vector on the center insulator post. If the was any point of failure I would expect it to be on the center insulator of the post adjacent to the misshaped bar.

I would recommend that any part of the installation where bars in each of the three phases do not have identical geometry (within the bounds of working tolerances) the bars should be replaced.

The main objective of industrial design is about function. If designing for function also makes it aesthetic that is a bonus.

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