Life Assesment

[Arevaengineer]

Hi Guys
Could anybody list standard tests for Life assesment of 11kV Air Insulated switchgear which is about 10 yrs old considering no maintenance has been carried out so far.What kind of test equipment would be required to carry out those tests.Would it be necessary to do mechanical endurance of switchgear and chemical analysis of the copper work?
thanks in advance

 

[ScottyUK]

10 years with no maintenance!

For life assessment top of my list would be partial discharge testing of the board. I can't imagine copper degradation being a serious problem unless you have a truly awful environment but if there is a signifcant H₂S presence then any silver plated components will probably be showing signs of distress. Silver turns jet black in the presence of H₂S. If you have PD problems then the breakdown products of polymer insulators form acids when they meet condensation. Rust on ferrous components and verdigris on copper are warning signs.

I don't see much benefit from endurance testing the breakers as the mechanical life is heavily dependent on correct lubrication and maintenance which frankly doesn't seem to be a strong suit of the equipment owner. That needs addressing - the last thing you need is a seized breaker mechanism. How many operations have these breakers accrued?


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

 

[trosepe]

Partial discharge test results are most useful for comparing results on the same equipment over a period of time.

The useful life of the switchgear depends mostly on maintenance, environment, loading and number of faults it may have cleared. Just the basic cleaning,lubricating and exersise on a regular basis can greatly improve the life cycle. The stored energy of the circuit breaker operating mechanism can do alot of damage if the circuit breaker is cycled with dry lubrication. I would do that first and do it properly; the proper lubricant in the proper places.

The springs on the stab finger clusters are items that fail early in life when not properly maintained (assuming this is draw-out equipment).

scottyUK asked about the number of cycles on the circuit breaker counter. That is important. Many cycles over ten years without maintenance would not be good for the life of the circuit breakers. Few cycles (<50)would be a good sign for extended life providing the owner gets serious about the maintenance and testing of this equipment.

Look up NETA maintenance testing specification for medium voltage switchgear. This will give you all the inspections, mechanical and electrical test specifications.

Well maintained switchgear in a resonable environment can have a life cycle of 40 plus years.

 

[ScottyUK]

"Partial discharge test results are most useful for comparing results on the same equipment over a period of time."

Agreed, especially if the PD level is low, but at any time it gives a useful indication of any existing faults before they become failures. Resin components within a switchboard such as breaker spouts and insulator posts are especially susceptible to PD if the board has had no maintenance and there are other contributing factors such as dirt, moisture, PD byproducts.


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

 

[rbulsara]

Follow NETA-MTS guidelines. You need to do necessary PM before doing any tests.

10 years without maintenance is suicidal. Although I have seen a data center with practically deferred maintenance for 20 years. The horror story that unfolded is too long and unbelievable and even hilarious, if you are not the owner!.



Rafiq Bulsara

http://www.srengineersct.com

 

[oldfieldguy]

I'd add thermography to the mix. We're fitting our new installations with viewports to allow us to do a thermographic survey without having to expose live equipment.

old field guy

 

[Zogzog]

To put this in perspective EPRI requires brealeks to be completely refurbished every 10 years. Not doing any maintenance is pretty bad, at least the NETA MTS tests. But with no OM's you may want to consider having them all rebuilt.

As far as the rest of the gear besides the breakers a PD test is the most info you get for your money. Easy test, no shutdown, finds many problems.

 

[trosepe]

ScottyUK,
No question PD is a valuable test for determining viability of insulation systems. I was trying a bit of sarcasm in that if the PD tests had been performed regularly, there would have been an excellent base for life assessment. I have a difficult time understanding 10 years without maintenance. A lawyer would have a field day with that if someone was to get hurt operating that equipment.

 

[ScottyUK]

Agreed on all points!


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

 

[Arevaengineer]

thanks to everyone for the valuable information.