High voltage maintenance

[jinglis]

I am trying to layout a preventive maintenance program for our 15 or so sites with customer owned high voltage equipment and cables. There is very little history of maintenance on these systems. Mostly we waited until problems arose and dealt with them. Some sites have gone 15 years with nothing done. We have started looking at these sites and doing shutdowns for maintenance. We have found some problems such as weather beaten stress cones, weak lightning arrestors, cracked overhead insulators and fuses, and load break elbows that would not release due to dry/lack of grease. These problems have been corrected and most sites are near 100% with a few more corrections to be made. Our contractor would like to see annual shutdowns ( good for him / expensive for us ) for cleaning, inspection, oil testing of transformers and testing of the equipment. This would allow us to forecast the lifespan of cables and predict major expenditures. Most of our sites are recreation and leisure buildings where an outage would be inconvenient but not the end of the world. I have done some calculations on the 10 year costs of these maintenance outages and see numbers from $175,000 to $215,000 based on frequency. I don't believe a utility does any preventive maintenance based on the amount of equipment they own. What are your experiences with this type of maintenance? How often should it be done? What is reasonable?

 

[iwire]

The company I work for has a division that does testing.

In many cases the customers insurance company is basically forcing these inspections to be done.

 

[jinglis]

What frequency do they require testing? I am struggling with the concept of spending 4 times the money for testing than the repair would have been worth.

 

[mikehughes8]

If your required to conduct maintenance obviously this will require testing. You mentioned oil testing. You need to indentify which oil tests you want to conduct. There are two basic types as you may already know; those that identify immediate serviceability of a transformer and those that assess the degree of aging. For immediate serviceability I would do dielectric strength testing to detect moisture content in transformers. Power factor testing can also be used for this same purpose. For general aging,you can use the interfacial tension, color, and acidity test. These should change very little from year-to-year. significant changes may indicate overheating of insulation system. Gas-in-oil-analysis is another test can reveal developing problem. EX: acetylene is only present if arcing has or is occurring.
If you decide to use a megger for insulation testing on oil filled transformers you results can vary +/- 50% each time. This is due to the nature of the insulating oil and the subtances that tend to polarize under application of DC stresses. In other words, its tough to get consistant data with a DC megger in liquid filled transformers. Verify all results if you go this route.
I would test yearly but its not a bad idea to do gas-in-oil-analysis more frequently.

 

[wcollinge2000]

if you are only looking at the cost of the repair to cost of maintaining the equipment then I would add what this is running is it for manufacturing or utility . where I work if a transformer goes down and it takes a week for us to get back up that well exceeds the 200,000 dollars in lost income for the company. we test and inspect once a year seems to be sufficiant. but fix any problems that are found . you have to look at all the costs. and I don't know but if your a utility and some one is loosing lots of money because of an outage and find out it is because of lack of maintanance due to somthing like that in this day and age they may call a lawyer to try to recoup the lost income due to the lack of maintanance scheduals.I bet the company would that I work for, I am almost sure of it.

 

[jcormack]

The frequency and type of testing should be related to the need for reliable service, the requirements of the owner for power, etc. Voltage levels should also factor in. We have a program that tests transformer oil with a fequency based on size, critical need, and voltage. A 138 or 69 kv transformer will be checked every 2 years, 25 kv every 3, 13 kv 3-4 yrs. Oil-filled circuit breakers are tested based on time (at least every 2 years) or number of trips. Circuit breakers are also untanked & contacts checked on a revolving basis. Oil can be filter pressed on-site, moisture can be vaccum-removed. Cables and surge arrestors should be checked on a regular basis, 50/51 relays should be tested/calibrated ......15 years is a long time to assume something is still as installed. Hi-Pot testing by its nature can be destructive, so that should be used judisiously. There are a lot of service companies that can bring out a truck to do basic oil-tests (BIL, opacity) TTR and powerfactor test on transformers, etc. We do a lot in-house, but bring in specialists to check CBs, relays, and large transformers.

 

[FNCnca]

We pretty well mirror the things that Jcormack does. One very important addition is IR scanning. We scan all high voltage gear and motor gear annually. And if time permits, we point the scanner at everything we can.

The few thousand dollars spent on this testing is nothing compared to the multiple thousands per hour lost on unscheduled downtime due to equipment failure.

 

[zog]

The NFPA 70B lists the frequency of maintenance tests and what tests should be performed. Another reference is the NETA MTS, whaich can be downloaded at www.netaworld.org

 

[Bill Swain]

This can/will be a much bigger issue sooner than later from what I read. The powers to be are going to make the rate you charge for electricity based on the reliability of your system. This could also give means for restitution for loss of service. I know some have had to deal with this, but unless there is negligence( lack of maitanence - I don't believe falls into the negligent catagory yet) you would be OK, unless there is evidence that you have recurring issues, but that would fall under remediation?????


"The frequency and type of testing should be related to the need for reliable service, the requirements of the owner for power, etc."

This part is already a negotiated part with some of our customers( ie. back up circuit, auto switch gear etc.)

Many place won't have big issues, but a lot of it will depend on the site conditions, which include cleanliness or lack thereof, type of loads, etc. , the answer will also debate the "need for reliability", cost of reliability, and how much down time is OK.

 

[brian john]

In our area four things drive equipment testing, some utilities requires it, the insurance companies, some local jurisdictions and customer's concern for safe reliable power.

Basically it is every 2 to 3 years (depending on who is pushing the issue). Many of our customers break it down (depends on their distribtion) with some portion completed every year.

 

[Reynolds White]

Deleted duplicate post from another thread. To see the post, click here.

-George