Lifespan of medium voltage copper bus bars

[buddy91082]

On average, how long can cooper bus bars last that are installed in a NEMA 15kV switchgear that is installed in a typical electrical room environment? I have gear that is installed from the 1960s. It looks in good condition but management is thinking of a full blown replacement of the gear. I am thinking we may de able to salvage the bus and enclosure and replace the breakers and relays. We would do testing of the bus to ensure it's still in good, physical condition. We would like to get another 25-30 years life out of it.

Thanks
c

 

[oldfieldguy]

The bus bars are generally NOT the problem. A careful inspection of insulators and supports for tracking and breakdown will verify condition.

With older switchgear, the problems generally arise with the interfaces with circuit breakers and other disconnecting means.

Many manufacturers have schemes by which to retrofit more modern and user-friendly circuit breakers and controls. This work is not uncommon. I have seen line-ups of gear installed in the 1940's with oil circuit breakers retrofitted in the 1980's to the latest iteration of vacuum breakers. It was a very nice and friendly installation.

Keep in mind that along with the electrical integrity, older gear also may have issues with safety, particularly in relation to arc-flash exposures.

old field guy

 

[ScottyUK]

Check the fault rating against the current HV network configuration. Many countries have reinforced their power grids over time, and what was once withing the rating of the gear often no longer is. Fault levels generally seem to go up!


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If we learn from our mistakes I'm getting a great education!

 

[gattie]

Your main busbar chamber may be of a vintage that is bitumen
compound filled.
Check that there is no evidence of leakage of bitumen from any of
chamber joints.
If there are leaks & consequent voids, you will have future corona
problems,& ultimate flashovers.

 

[Zogzog]

The bus is rarely an issue, as mentioned, the breakers themselves are usually the issue. You have several options.

Refirbishment of your existing breakers, depending on what you have the manufacturer has recommended times/cycles that they recommend this is done. Nuclear plants for example refirbish thier breakers every 10 years. If done properly they can be brought back to a good as new condition.

Roll in replacements for your existing breakers. THere are usually several options for this which allows you to upgrade to modern VCB technology at a fraction of the cost of replacement. The advantage to this is a very short downtime. The way we usually do these is to deliver all of the replacement VCB's and then take trade in for your old stuff after you swap them out.
Here are some similar projects

http://photos.gcbsinventory.com/references/

Replacement of switchgear. Expensive, very long down time. But, you can upgrade to arc rated switchgear.

 

[ScottyUK]

Disadvantage of vacuum gear is that the current chopping which occurs, especially at low current, and the high voltages which this induces. OCBs generally don't suffer from this problem. Motors in particular can suffer if measures aren't taken to control the induced voltage.


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If we learn from our mistakes I'm getting a great education!

 

[gattie]

Insist on operational speed traces for each replacement VCB.
As ScottyUK advises, vacuum breakers have been known to cause high voltage spikes.
MV Motors should be protected with surge arrestors - particularly
where windings are Mush type.