Reclaiming Oil

Reclaimed Oil?

  In the past I have had many engineers ask me just how good is reclaimed oil? My answer is that it depends. When using reclaimed oil several things have to be taken into account.

1.     It goes without saying that the oil must be PCB free. Only a small amount can contaminate anything that it gets mixed with. On this issue we must look to the future and assume that sometime any PCB’s will be totally banned and we will have to dispose of them. In that case there’s no need to create any additional problems by adding it to non-contaminated oil.

2.     Where did the oil come from? Assuming that it is PCB free if it came from an OCB and has not had all of the carbon filtered out it may do more harm than good.

3.     What is the before level of moisture in PPM. After?

4.     How was the oil reclaimed? Was it just pumped through a filter press? Was it vacuum dried? Did it pass through a bed of active alumina or fullers earth? Know what the process is before you use it.

5.     What is the history of the unit that it was in? Did it explode? Was it very old? Why was this oil available to reclaim?

6.     How long since it has been processed and how was it stored?

These are just a few of the things that you should be thinking about before using or reclaiming oil. Properly reclaimed oil should perform as well or better than new oil if it has had the correct chemicals added such as oxygen inhibitors to slow down the oxidation process. DBPC is what has generally been used over the years. It has to be injected into heated oil as it will not dissolve into the oil at normal temperatures. Oil that is 20, 30, 40 years or older is actually a higher quality base product than the oil processed today.

A quick check of the internet can turn up several oil reprocessors that will come out to your site to perform the work. Since they usually come from quite a ways it takes quite a bit of oil to make it worth your while. You can always buy your own machine but unless you perform this function daily it’s best to leave it to the experts. If you do own your own machine you will find it harder not to cross contaminate your oils, another reason to leave it to those experts.

I have already mentioned PCB contamination in this article in addition to that danger you should also be aware of moisture contamination. Most processors won’t tell you that the adsorbent media that they use (fullers earth) can transfer moisture into the oil. In the reclamation process the oil first goes through a heating cycle, then it passes into a vacuum chamber that degasses and boils off any moisture that may be dissolved in the oil. The final stage for the oil is to be passed through an adsorbent bed of fullers earth to remove acids and sludges that have built up over time. If the moisture content of the fullers earth is greater than that of the oil…guess what! You’ve got it! The moisture level balances out and the oil can be returned with more dissolved water than it had to start with. This is not a good situation if you are having a tank of oil reclaimed. It’s downright disastrous if you are having the oil in a transformer reclaimed. When reintroduced into the equipment the moisture will immediately go into the paper insulation as it is much more hygroscopic than the oil.

BONUS QUESTION!!!!!
A question for those of you who are familiar with reclaiming transformer oil.

Name one of the ways to stop oil from foaming too heavily in the vacuum chamber.

A correct answer will net you 10 points!

I will continue information on reclaimed oil in my next post. I will also be dealing with energized oil processing.

If you have any questions or comments, please let me know.

If you haven’t yet purchased your copy of my gas analysis program now is a good time. Just fill in the data below. All of the comments that I have received have been positive so that’s a good endorsement from you the users.

Don't forget to leave any comments or suggestions that you may have. To contact me directly just email me at transformerbob@gmail.com. I want you to know that I do appreciate my loyal readers and I will continue to produce content that you are piques your interest.

Today’s Quote: “The towels were so thick there, I could hardly close my suitcase” – Yogi Berra

Best Regards,

Bob

Product News! Product News! Product News! Product News! Product News! Product News!

I just finished the customer version of my GC analysis program.  When I was working I always used my own program to verify the lab’s gas analysis test results.  Now I have a copy that you can use too.  This program is:

·         Simple to Operate

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From the comments that I’ve gotten, this program is well worth it. Just click on the button below for your copy. As soon as I get the word your CD will be on the way!  All shipping within the states is included in the cost of the program!

Thank You!

Bob

Quantities

1 copy $159.00 USD 10 copies $155.00 USD 25 copies $145.00 USD 50+ copies $125.00 USD

Sampling Procedures for Oil Screening Tests Continued…

Before you read my blog………

Since I have retired from the transformer business I thought it might be a good idea to make some of the tools that I developed for myself available to operations people out in the field.  One of my most useful tools was my dissolved gas analysis program.

 It was used to analyze the test results generated from the gas chromatography test on transformer oil. All of the testing labs will give you a conclusion with the numbers generated from the test but I never had complete faith in their analysis. They never tell you how they reached their conclusion or what method they used. I used all of the major methods and then made decisions based on data from all of the major methods of analysis in use today.  What I found most of the time was that inevitably one ore more methods might point to a potential problem while the others ignored it, or said that it was insignificant.  

I have rewritten the program to make it easy for you to use and simple to understand. I am making it available to you on CD for Windows compatible computers. With this program you will be reassured that the data you are getting has been thoroughly scrutinized and the judgments that you make concerning the data are sound.  Isn’t it always more comfortable to have a second opinion?

Normally tests are performed yearly and with this in your toolbox you can instantly verify any potential problems or normal running equipment.

All you have to do to get your copy is click on the button below.  I will send it to you immediately.  If you want to order additional copies for people on your staff or at satellite locations quantity discounts do apply. 

For not much more than the cost of a test you can have peace of mind. Isn’t that something that can make your job just a tad easier?

Thanks,

Bob

Quantities

1 copy $159.00 USD 10 copies $155.00 USD 25 copies $145.00 USD 50+ copies $125.00 USD

Attention:

And Now to the current post of my blog…..

Sampling Procedures for Oil Screening Tests Continued…

We are pretty close to being able to draw the oil sample here but I just want to mention a word about PCB contamination. The tech who is doing your sampling should be bringing in clean, PCB free accessories to obtain the oil sample. First of all you should know which transformers have levels of PCB’s and the quantity in parts per million. The tech SHOULD be using new tubing and a siphoning device. They don’t cost very much and will assure that you do not contaminate your equipment further with PCB’s from someone else’s site. I feel that it’s best to set this up when the tech calls you for scheduling. Tell him or her that you expect them to be packing new tubing, siphoning devices and if not new, alt least washed out fittings and nipples to screw into the valves. They can be washed out with an appropriate solvent and your substation escort should check them to verify the fact. Make a route map for the escort and leave all of the transformers that do not have valves and require siphoning for last. Then make a route for them that starts with the lowest level of PCB contamination and ends with the highest. For the larger units that require fittings and nipples, make sure that the tech flushes everything adequately.
Most transformers come equipped with standard brass gate valves at the bottom for filtering and draining. That is where the sample should be drawn from. If a tech uses a small sampling port on the side odf a large valve he is just being lazy. To get an accurate sample the main valve should be used. Breaking this down into steps first the technician has to remove the plug in the valve. Normally oil has seeped through and there will be a small amount that runs out from the valve body that should be discarded in a waste oil container. Then the technician will probably screw in a reducer with a ¼ inch nipple attached. The tech must then flush the valve THOROUGHLY. This means at least three times the volume of oil that would fill the valve cavity along with any piping that is attached. This way he is assured that the sample comes out of the tank itself and not the connections between the tank and the valve. Another reason for this is to flush any condensation that could have been deposited in the valve cavity due to temperature changes. It only goes without saying the contained used needs to be clean. After the valve is thoroughly flushed the sample container should be half filled with oil from the valve, shaken and then emptied…twice to assure a clean sample. After that the container needs to be filled, capped tightly, identified, and stored for testing within a few days.  Sample containers should be clear or at least translucent. The technician needs to hold the sample up and take a good look at it before putting it away and moving to the next unit. Samples should be allowed to “rest” and settle for at least a few minutes before being stored. Any sediment, free water, or debris observed in the sample dictate that another sample must be taken following all of the above procedures for flushing out the valve. It should be marked as a second sample and stored with the first. This will help to eliminate any questionable data that might be observed with just a single sample. At the end of the day when the samples are allowed to cool they should be checked again for any sediment or free water. If anything is observed and there is no second sample there is always time to go get a second one.
A good tech will clean up and leave the substation spotless, double check that the valve handles are tight, tighten any loose packing nuts and generally leave things looking better than when she or he arrived. You as the owner should take charge of all of the waste oil and waste product. This can prevent any problems that could arise later if someone ends up dumping the waste in the wrong area due to ignorance or negligence. You are legally responsible for the waste. It is more convenient for the technician if you take it as well. Make sure that you get everything. The tubing used and the siphoning device as well. These are inexpensive and the tech should have spares.
If the oil is being shipped to a central lab, check the packaging to make sure that no incidents can occur. You may also want to eyeball the labeling to make sure that it has been properly sealed and marked assuring that none of the samples are mixed up.
Test results should come out to you within two weeks. If it takes any longer than that either the lab is backed up and the samples sat around longer than they should have or the lab is disorganized. Check thae data printed on the sheets and compare it with your escort’s notes carefully. If any problems, other than high acidity/low IFT, are noted check to see whether or not the tech drew another sample.  If he/she didn’t, make sure that you ask for a freebie retest for verification. (note: also if the acid/IFT numbers are not  close to the previous test result ask for a freebie retest).
I think I have covered almost all of the standard procedures in sampling for oil screen tests. If you have a question regarding any unusual cases (or if you just have a question) please email me at transformerbob@gmail.com.
Please send some feedback and let me know what you would like to be covered in the next post.
Oh Yeah! Don’t forget to order your Dissolved Gas Analysis evaluation CD. I guarantee you it’s well worth it. Just send an email to transformerbob@gmail.com.  It’s your decision but remember it’s a  small investment for a large tool in your toolboxes. I have already received some very positive comments on it. Just use the shopping cart button at the top of the blog. And Thank you!
Regards,

Bob
Quote of the day:
“An investment in knowledge pays the best interest”
He also said:

“A countryman between two lawyers is like a fish between two cats. “Benjamin Franklin

 

Sampling Procedures for Oil Screening Tests

Before you read my blog………

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Thank you,
Bob

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1 copy $159.00 USD 10 copies $155.00 USD 25 copies $145.00 USD 50+ copies $125.00 USD

Attention:

And Now to the current post of my blog…..

Sampling Procedures for Oil Screening Tests

In this post I will discuss sampling procedures for the oil screening test. First I want to mention that samples should ONLY be taken by experienced qualified personnel who are fully aware of the dangers involved in being around high voltage equipment. This is by no means an instructional manual on how to sample transformer oil. It is meant only to educate and so that you the reader can know whether or not the tech that you brought in to perform the sampling has done an adequate job. I cannot be responsible for any yahoo that reads this and thinks he or she can do it themselves. Again, please leave the sampling up to the experts. They know what they’re doing and how to do it without injury. Even then I have seen several accidents occur when the tech lost his focus.
There are other liquids used in transformers but here we are only discussing those filled with mineral oil. Mineral oil being lighter than water, therefore the sample should be taken at the lowest point available on the transformer.
When first approaching the equipment the technician takes note of several things such as the weather, the location of possible sampling points, the overall conditions in the substation, the proximity of current carrying components, cleanliness, lighting, leaks etc. These conditions should be recorded and kept with the sample because they will figure in to the evaluation of the sample when testing is performed.
Weather- Is it rainy or sunny? If the tech isn’t willing to cash it in because of rain then use another company, chances are good the results will be fudged. For emergency purposes sampling can be performed in the rain but an uncontaminated sample is a lot less likely. Even if the substation is indoors rainy weather should be noted in case the sample containers got wet. Sampling in the rain for an outdoor substation is not recommended for other reasons as well. One never knows when a lightning strike may occur and if it does that’s not the time to be hanging out in a substation.  It really doesn’t take an Einstein to know that the best time to take a sample of oil is during dry sunny weather.
Note the ambient temperature. Is it hot or cold?  Cold weather can cause the oil to contract creating a vacuum in the tank. A good tech always takes note of the ambient temperature, then checks the temperature gauge on the equipment along with the red line on the gauge for the maximum temperature. Then the tech will carefully touch the tank with the back of his/her hand to confirm what the gauge says. In about 5% of the cases they don’t work. If there is no gauge present the back of the hand will have to do. The tech uses the back of his/her hand for a couple of reasons, 1. The skin on that part of your hand is more delicate and senses temperature better than the tough skin on the palm, 2. If there happens to be something like a grounding problem and the outside of the equipment is energized your muscles will contract. In that position your hand will not grasp anything that it could lock on to. The tech should be trained to use the right hand for this. Using the left could cause current to pass through the heart causing fibrillation and stopping the heart.
If the transformer is cool to the touch and the weather is cool as well it’s wise to check to see if the transformer is under a vacuum. Most of them have gauges that you can check. Don’t always believe what it says. Tap the gauge. Look at the tank, if it looks like it’s sucked in a bit then there could be a significant vacuum on it. There is usually a nipple under the vacuum gauge. First check to see if it’s dry because there could be water in it or debris that can be sucked in. While holding your finger over the nipple release the valve under the gauge to check for vacuum. If a vacuum does exist, get a tank of dry nitrogen along with a regulator and a clean clear plastic tube. Be careful how much that you add to the top airspace. Remember that if it’s very cold out the pressure will increase when it warms up. That could blow out some gaskets and cause leaks. Use your best judgment but in any case if it’s cold out never increase the pressure to any more than two lbs. preferably less.  If you should try to drain a sample with a vacuum on the top airspace the unit could suck air in from the bottom valve causing air to bubble up through the tank Causing  arcs and sparks (one of the functions of the oil is to contain the voltage). Worst case scenario could be an explosion. Also after a rain I have seen water collect in a valve if it has not been plugged. That water can get sucked in along with an air bubble and be immediately distributed through the system. Don’t think that this can’t happen because it has happened to me. I got as far away from that piece of equipment as possible until the water settled in the bottom of the tank. As an additional note don’t forget to check for sudden pressure change shutoff relays. These relays will kill the power at a sudden pressure change and can cause real problems if the transformer is powering equipment that runs on a continuous processing line (been there too!).
When the tech checks the redline on the temperature gauge, records it and resets it, he or she should also take note of leaks. Did the temperature rise so much that it pushed oil out through the gasketed portions? Does it look like the gaskets are still leaking? Check the oil level. First check the gauge then feel up the side of the tank for a temperature difference at about where the oil level should be. If it’s hot, is it below the top level of the cooling fins? Why? Where did the oil go?
Look for safety issues like limbs or plants growing across the power lines. Is there garbage in the substation? Most of these are fenced in, is there a lock or some method to restrict access to the substation?  Are the cooling fins free or is there something restricting the airflow? How about the condition with respect to corrosion? Is the paint all faded, is the unit rusty? What kind of paint is on it? If it’s a metallic paint such as a silver or aluminum color you can bet the transformer runs about ten degrees hotter than if it were painted with just white enamel.
Check the valve. What type is it? How does it look? Is the packing leaking? Is it a brass valve? The reason for this is that in older days many manufacturers used a “cider press “ valve. Just like the ones used on your gas line at home. They were meant for minimal use. The proper method of opening that type of valve is to loosen the nut underneath, then gently tap upwards on it loosening the tapered portion. Then it can be easily turned about ¼ turn with a crescent wrench from the top. A lazy or less than knowledgeable tech will just try and turn it from the top. Most of the time it will work but all it takes is once for the taper to shear off and your stuck with a gushing stream of oil that you’re not prepared to stop. It’s always good to be prepared with a “C” clamp that can be fitted around the top and bottom of this type of valve for a temporary field repair should a break occur.
If the unit does not have a valve on the bottom look for access at other locations. Most transformers have gauges that can be removed or plates near the top. In this case the technician needs a siphoning device attached to a tube that can reach the bottom of the tank. This is one the second worst scenario that you can encounter because it puts you in proximity of the wires. A very close friend of mine found a small plug that he could remove near the top of the transformer so he could feed a small tube in to siphon a sample. Problem was that the incoming lines were carrying over 7200 volts. As he cranked his crescent wrench down on the plug, his head dropped along with the rest of his body. He came too close to the wires and the power arced across the gap and blew off the bottom of his ear. Luckily he survived to tell the tale. Another reason that it’s worth every dime to have an experienced technician draw the sample. Finally if the unit does not have a valve or any other access if the bushings are not located on the top of the unit an experienced tech can remove the top and siphon out the sample. Believe me this is much easier said than done.
All of that said we are just about ready to draw an oil sample from the transformer, but as I’m looking at my watch I have run out of time and will have to leave that for the next posting. Looking at the previous two pages makes me wonder how many of you thought that it was this easy just to get to the point of drawing the sample?
As always if you have any questions, comments, input, or output please email me at transformerbob@gmail.com.  
The quote of the day is:
“I bet after seeing us, George Washington would sue us for calling him "father." Will Rogers

Oh Yeah! Don’t forget to contact me to get your Dissolved Gas Analysis evaluation program. I guarantee you it’s well worth it.   It’s a small investment in your toolboxes.
Thank you,

Bob

A Word About Transformer Oil Color

A Word About Color

I need to add a few words about color here. Color is pretty much just an observation. It becomes more relevant when you compare it from previous years. Oil that has been heated during a reclamation process will usually show up at about a 2.0. The color will be just a bit off from the disk on the colorimeter because it’s been “roasted”. The acid and ift numbers will show up fine on these. If over a few years it starts to drop rapidly then you know that the oil reclamation process did not do a good job of cleaning out the sludge. Probably a result of too little exposure to the filtering media and hot oil. It could also be due to an incomplete draining during an oil change out. Again future tests will reveal the process.
I have seen some oils in that were new and they were at a 4.0 to 4.5 on the colorimeter. I remember the first time I ran across these and was mystified as to why the oil test results were showing up as good. It was explained to me that that was an oil produced for Westinghouse corporation and it was used in a lot of units. You can identify it first by the test results and second by the bluish cast that it has when held up in sunlight. Anytime you get an oil with a 4.0 or better color you still had better sniff it to assure no arcing or overheating.

For those of you that are visiting my blog I want to thank you and make an offer that you can’t refuse. I am currently working on a program that I can post on the blog site that you can use to evaluate your own oil screen test results oil screen consists of Acid, IFT, Color, Dielectric, Specific Gravity, Visual, and Sniff tests). If you send me your results at my e-mail address I will look at them for you for free and send you back a short evaluation sheet. Just send them to: transformerbob@gmail.com. Allow a little time for me to evaluate because I don’t open up my email every day.
Thanks and Best Regards,

Transformer Bob

“Good breeding consists in concealing how much we think of ourselves and how little we think of the other person.”

MARK TWAIN, Mark Twain's Notebook

Transformer Oil Acidity and Interfacial Tension

Transformer Oil Acidity and Interfacial Tension

Continuing on we have to look at the acidity level and interfacial tension of the oil. These readings should always be compared together. As oil oxidizes over time it begins to create acids within the solution. This process can be greatly accelerated by heat. In normal conditions it takes many years for the acid levels to reach a point where servicing is needed. Most transformer oil has an inhibitor added to slow down the oxidation process thereby extending the life of the equipment. Chemically what happens is that the oil molecules have spaces reserved in them that oxygen atoms will fit into perfectly. The inhibitor molecules fill up those spaces (although not as perfectly as an oxygen atom) until they are forced out at a later date by oxygen atoms. When this happens the acids formed begin to attack the tensile strength of the cellulose materials (wood and paper) in the transformer making them brittle and subject to cracking due to constant vibration. As a byproduct the formation of acids produces a tarry like substance in the oil that we call sludge. The best way to visualize sludge is to think of it as asphalt. It will deposit on the horizontal surfaces of the transformer and harden causing a furthering of the brittleness. So sludge in a transformer is a direct result of the acid formation in oil.
Acidity levels are measured on KOH per gm. KOH is potassium hydroxide and is used to neutralize the acid. The test technician will put enough drops of KOH into a measured mixture of oil and isopropyl alcohol to turn the sample pink and hold. Then he/she calculating the amount of KOH used in a set formula to render a neutralization number. This is a pretty straightforward test. There is some variability in that the technicians’ judgment is employed in determining the correct shade of pink but it’s so simple that most technicians can come up with reliable results easily and there aren’t many things that can throw off the test result. An extremely dark color can also make testing difficult.
The interfacial tension test is a test that must be done by an experienced technician to get valid results. It takes quite a bit of experience to generate reproducible IFT tests. If it’s not something that the tech does on a regular basis you would want them to run it at least three times. Interfacial tension is reported in units of force or dynes per centimeter. The technician must be knowledgeable, have steady hands, use clean equipment and have a clean sample. To better understand how delicate the test is the IFT of clean distilled water should be somewhere around 75 to 80 dynes per centimeter. That is the force that it takes to penetrate the surface of the water. That’s why some insects can “float” on top of the water without getting wet. They aren’t heavy enough to penetrate the surface.
In performing the test a sample of uncontaminated distilled water is poured into a beaker sitting on a platform mounted on the IFT instrument. The water needs to cover a platinum ring suspended on the apparatus that protruded into the beaker. The technician must then carefully pour some of the oil into the beaker slowly so that it sits upon the water. Normally about ½ to ¾ inch of water and about ¼ inch of oil. The platform is then loosened and the ring is carefully placed at the top of the water level just at the interface of the water and oil. The ring is then released from a locking device and it should float motionless in the mixture. The platform under beaker is then slowly lowered using a screw knob by the technician’s left hand. At the same time the technician exerts upward force on the ring by turning another screw knob in his right hand. Care must be taken to assure even pulling in each direction. What will happen is that the ring will get dragged down and resist breaking the surface of the water into the oil. When the ring does break the surface it will jump into the oil. At that point the technician stops and makes note of the reading on the dial of the instrument. This test requires coordination and a very delicate hand. If the readings don’t make sense then it should be repeated for accuracy. There is a plethora of reasons why an IFT test can go wrong.  The ring and beaker must be clean and free of any residue of soap. Soap will break down the interfacial tension of the water to prove this carefully place a needle on a sample of distilled water on a clean beaker. It sits on top of the water and will not sink if carefully placed. Add a drop of soapy water and it will immediately sink to the bottom. The soap has broken down the interfacial tension of the water. The ring must be cleaned and all residue removed before the test. Normally a dip in alcohol will clean it adequately.
Most of the time comparing the two will confirm a correctly performed test.  
If the neutralization number is between 0.00 and 0.10 the IFT should be between 30.0 and 45.0
If the NN is between 0.05 and 0.10 the IFT should be between 27.1 and 29.9
If the NN is between 0.11 and 0.15 the IFT should be between 24.0 and 27.0
If the NN is between 0.16 and 0.40 the IFT should be between 18.0 and 23.9
If the NN is between 0.41 and 0.65 the IFT should be between 14.0 and 17.9
If the NN is between 0.66 and 1.50 the IFT should be between 9.0 and 13.9
If the NN is greater than 1.51 its safe to say you have a problem.

What do you do if they are not in the above ranges? Same as above, we go back to the history of the transformer. If the NN is low and the IFT is low was the oil changed in the transformer? Look at the color was there a lightening from the last test?  If the color hasn’t changed was the oil filtered in some way? Possibly a “cold” oil reclamation process? Did you repeat the tests? How do they compare from the previous data if any?
What if the NN number is too high for the IFT? Check for a marked color change. Has the unit been overheating? If it is overheating is the oil at the proper level or is it low? If it’s low why? Is there a leak?
Make sure the sampling apparatus is clean, uncontaminated and that the technician knows what he is doing when he draws the sample. (Sampling will be discussed in a future post)
Finally confirm that you have the right sample. It’s easy to mix them up.

Specific Gravity is not really a test. It’s merely recording the number and comparing it to past observances. The specific gravity device used to measure most oil samples is not a precise instrument and the number that you get from it is a ballpark. The specific Gravity of water is 1.0. I have seen uncontaminated transformer oil anywhere between 0.865 to 0.890. If the oil is grossly contaminated with PCB (well over 1.0, usually about 1.5) it will be above the 0.890 mark. In many cases you will be able to detect PCB contamination just by sniffing a sample. A few manufacturers dipped the windings in PCB for testing (the test facility was indoors) back in earlier days. Those transformers have high specific gravities accompanied by a strong PCB smell.
Visual test is an observation looking for particulate matter like filter media residue or degrading cellulose material. If the sample has any free water it can be seen at the bottom of the sample. As mentioned in the other tests above if you see something in a sample that is not supposed to be there you have to begin an investigation of 1. What is it? 2. How did it get there. Again most times a second sample should be taken. If it looks like cellulose further more extensive testing should be done. In the case of water if the second sample shows it Karl Fischer tests should be performed to determine how much is in the oil and windings. GE made a great nomograph precisely for that purpose. You can find it in many places on the internet.
The sniff test is just that. The technician has to sniff the sample and determine if there is any unusual odor present. A good nose can detect arcing, overheating, PCB’s or other problems. As with the above tests always put things together and compare all of the other tests when you get an unusual result. It will help lead you to potential problems. Sometimes it will force you to perform other more expensive tests but if you saved the equipment it’s mostly worth it.

I’m working on a spreadsheet that can analyze oil test results for you  to post on my website Transformer Oil for Dummys.  Remember if you have questions email them to me at transformerbob@gmail.com. 

Regards,

Bob

“You can always count on Americans to do the right thing—after they’ve tried everything else.” – Winston Churchill

Field Testing of Oil Filled Transformers Part 1

Field Testing of Oil Filled Transformers

Field tests performed on transformer oil consist of:

Dielectric Test

Specific Gravity*

Color*

Visual*

Acidity

Sniff test*

Interfacial Tension

*Note Specific Gravity, visual, sniff, and color are not really tests, only observations for later comparison.

Dielectric  testing is performed with a hypot. A sample of oil is poured into a cup that has two electrodes set at 1/10 of an inch apart.  A controlled gradually rising current (from 0 to 50Kv) is applied to the electrodes until an arc jumps across the gap. The meter then stops and the breakdown voltage is recorded. The unit is reset for another test.  The technician performs three such tests on a sample then averages the three to come up with a reading.  For most observers any average that comes out to 27Kv or better is sufficient. Any readings lower than that can indicate a problem in the insulating value of the oil. 

When an unacceptable dielectric test occurs the testing technician first has to look at several factors. First, what does a visual observation of the sample reveal? Is there dirt carbon or other contamination suspended in the sample? Look at the bottom of the sample is there any free water present?  Was the sample collected in a clean uncontaminated container? Was the drain valve properly flushed? Was care taken to make sure that the sample was not contaminated by the technician’s hands? Is the hypot working properly? Is the electrode gap set correctly? Was there any contamination left in the cup from a previous sample?  A lot of things can make a dielectric test go south so it’s always best to confirm the readings with another properly drawn sample.

If the second sample renders an unacceptable reading as well then go back to the previous paragraph and recheck all of the items listed.  If the visual shows particles either at the bottom or in suspension then you must try to identify what the particles are.  Carbon in a sample will settle over time and create a black covering over the bottom of the sample container.  When the oil stirs carbon will wisp up looking like smoke in the liquid.  By the way, in case you haven’t guessed your sample should be taken in a dry uncontaminated container that you can see through such as a clear plastic or glass bottle.  If the sample has particles in it try to identify what it is. Anytime you have oil with particles in it I would say it’s not good.  It can be deteriorated paper or wood from the inside of the transformer or it could be media material from a filtration or reclamation process. Most of the time paper or wood from the inside of the unit will not cause a breakdown in the dielectric properties of the oil. They are good insulators, that’s why they are used inside the transformer. Experts may disagree somewhat and speculate that the deterioration of the cellulose material in the oil created a byproduct of moisture in the oil so further testing could be required.

Free water in transformer oil is the easiest to spot. Oil and water don’t readily mix and if you look closely free water will show up as tiny beads in the bottom of the sample container.

Now it’s time for a little research.  First look at the unit. Is it a sealed tank or is it open to the air? If it’s sealed does it have a positive pressure on it or a vacuum? If it has a positive pressure find out if they put a nitrogen blanket on it or something else? If something else then what? If the tank has a vacuum or the pressure/vacuum gauge reads zero check to see if there’s any water sitting on the horizontal surfaces of the tank.  If yes has there been significant temperature fluctuation lately? Could the unit have heated up in the daytime and when it cooled down at night sucked in some water sitting on it? Open or closed has there been any precipitation lately? Has the unit been serviced in some way? What was it serviced for? How was it serviced? What equipment did they use? Was the oil filtered? Was it changed out? Sometimes filter paper can absorb enough moisture from the air to add it to the oil. Thorough research can, in most cases, uncover the reasons for an unacceptable test without having to perform further tests. However keep in mind that further testing needs to be done to confirm what you may have narrowed down as the source of the problem.  A Karl Fischer Test looking for parts per million of moisture should be done. If the Karl Fischer test shows the moisture to be within limits then there could be something in the oil like fibers from the filtering media or some other difficult to spot contamination in the oil. As I said above, a little research can usually dig out a problem like this.

A color comparison may give some clues as well. Transformer oil darkens very gradually over many years.  If the oil is one digit or ½ digit different from the last observation it could just be the opinion of the tester.  It may have been slightly lighter or darker than what the colorimeter slide was showing and was recorded according to the judgement of the testing technician.  If you can go back further and find earlier test results a tracking of the progression would be helpful.  If the oil is significantly lighter (by more than 1 digit) it probably indicates that the oil has been changed out. Significantly darker could indicate an overheating problem,  the oil may have been reclaimed with an oil reclamation unit, could have had some darker oil added to it, or there could be something going seriously wrong in the transformer.  First give the oil a sniff. What does it smell like? Could there be any foreign contaminants in it? Something soluble that would mix with the oil? Does it have a burnt smell? Check the temperature gauge and feel the tank with your hand to confirm it. Most temperature gauges have a recording needle that gets pushed to the maximum temperature reached that doesn’t recede when the current temperature recedes. What does that maximum figure read? Is it unusually high?  If so try to find out why. Was there an unusually high load placed on the unit for a period of time? Was the air restricted in some way so as to not be able to flow over the cooling fins? Feel the tank and the cooling fins to make sure that the oil is circulating through both.  Along with all of the observations a color change mandates a dissolved gas analysis to rule out several potential problems. 

I’ll continue on my next post and discuss acidity. Remember if you have questions email them to me at transformerbob@gmail.com. 

Looking forward to writing again soon.

PS Check out the website I’m setting up at Transformer Oil for Dummys.

Thanks,

Bob

The holy passion of friendship is so sweet and steady and loyal and enduring in nature that it will last through a whole lifetime, if not asked to lend money.

MARK TWAIN,

Oil Filled Transformers 101        First Post July 2011

This blog is to introduce you to the maintenance testing and care of oil filled transformers. I have spent 15 years in the industry in my younger days and now I think it’s time to start disseminating some of the insider knowledge about the testing servicing and repair of oil filled transformers.

We could see the market beginning to shrink years ago. When the first president Bush made the declaration that we were going to a service economy it pretty much sounded the death knell for the growth aspects of the industry. I knew that in the future everyone would be fighting over a much smaller pie.  Most of the huge industrial plants are gone due to inefficiency, high labor costs, higher costs of doing business due to regulation and other reasons.

What we are left with is a few small manufacturers and utilities who own their own transformers.  With fewer manufacturers, testing and maintenance is becoming more and more important to those few. In the decade of the eighties it was customary for owners to just run it until it blows rather than invest in testing and maintenance.  Only those that absolutely could not afford a shutdown were interested in testing and PM. Utilities usually had spares on hand to replace the smaller KVA units and only performed testing on the larger more expensive units (some of which take months/years to replace).

Testing and maintenance companies had come up with the theory that a transformer theoretically could last over 400 years if properly maintained. That worked out great for business but when the customers learned how much they could save by purchasing newer much more efficient equipment they lost a lot of wind in their sails.  The industry quickly recognized that this turn of events could be beneficial because the newer equipment was built with virtually no safety margin. It not only ran hotter causing it to deteriorate faster and it could not stand up to the abuse and fluctuations that the older transformers could handle with ease.  

Basically you only have a few materials in a transformer:

Oil

Wood

Iron

Steel

Copper

Paper

Ceramic

Some cloth or plastic/rubber type insulation

And some cork or other gasketing material

The iron, steel, copper, and ceramic will easily last 400 years if protected from corrosion. It’s the organic stuff, the oil, paper, wood, gasketing that deteriorates, and the whole process is fueled by oxygen and heat and aggravated by vibration.  We will get into all of the details of this process later.

Some of the companies take oil samples for testing without power shutdown. If shutdown is not possible then you should be testing this equipment on a regular basis.  This is something else that we will be discussing in detail at a later date. That being said ALWAYS leave energized sampling to the experts, the people who do it everyday. There are so many hazards that could trip you up and a mistake can be fatal.

As I told you above this is an introduction to Oil filled Transformer Testing  Maintenance and Repair. I would appreciate any feedback from you on any of the writings here as well as any questions that you may have. Subjects for future logs will be:

Field tests

Lab Tests

Dissolved Gas Analysis

Moisture

Re-gasketing

Filtering

Oil Reclamation (Energized or Shutdown)

Leak Repair

Painting

Bushing and insulator repair/Replacement

Vacuum Processing

Heat

Interpretation of test results

And anything else that I may be able to help you with.  As far as direction, I will take this blog anywhere YOU want to go by your questions (within my areas of expertise). Please don’t hesitate to email me at TransformerBob@gmail.com.

Best Regards,

Transformer Bob

"Classic." A book which people praise and don't read.

MARK TWAIN, Following the Equator