Transformer Oil Testing

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Pratik Trivedi Participant Join Date: Jul 2013 Posts: 2	Transformer Oil Testing 07/16/2013 6:45 AM
	Can anybody tell me that why we keep 2.5 mm gap between two electrodes while transformer oil testing?
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#13 "Re: Transformer Oil Testing" by Shyam on 07/17/2013 12:14 AM (score 2)

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#9 "Re: Transformer Oil Testing" by Shyam on 07/16/2013 10:43 PM (score 1)
#15 "Re: Transformer Oil Testing" by dhgrant on 07/17/2013 10:02 AM (score 1)

Tornado Guru Join Date: May 2009 Location: Richland, WA, USA Posts: 21017 Good Answers: 795	#1 Re: Transformer Oil Testing 07/16/2013 6:47 AM
	So they don't short out to each other, for one guess. __________________ In vino veritas; in cervisia carmen; in aqua E. coli.
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PWSlack Guru Join Date: Jan 2007 Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on. Posts: 32175 Good Answers: 839	#2 Re: Transformer Oil Testing 07/16/2013 6:51 AM
	The person that authorised the test protocol for use certainly can. Has the question been asked? __________________ "Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
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lyn Guru Join Date: Oct 2008 Posts: 42355 Good Answers: 1693	#3 Re: Transformer Oil Testing 07/16/2013 9:20 AM
	Try a little search. Transformer oil testing - Wikipedia, the free encyclopedia dielectric strength tester for isolating oils ot-60 And finally; IEC 156 Standard Transformer Oil Insulation Testing Equipment ...
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Candlez Commentator Join Date: Apr 2011 Posts: 57	#4 Re: Transformer Oil Testing 07/16/2013 9:29 AM
	It is based on: The minimun insulating oil acceptable break down voltage value Also Safety consideration to avoid application of very high and dangerous voltage to break down the transformer oil, yet doesn't break down at a lower value than acceptable value say 50Kv of a healty oil
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PWSlack Guru Join Date: Jan 2007 Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on. Posts: 32175 Good Answers: 839	#5 In reply to #4 Re: Transformer Oil Testing 07/16/2013 11:35 AM
	...the detail of which, and the test-specific values for which, may be found in the test procedure that the original poster has concealed from the forum... __________________ "Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
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lyn Guru Join Date: Oct 2008 Posts: 42355 Good Answers: 1693	#6 In reply to #5 Re: Transformer Oil Testing 07/16/2013 11:41 AM
	In defense of the OP, I'll wager that he has no idea what test he is supposed to be conducting. Nor the ability to carry out such tests, should they become known.
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PWSlack Guru Join Date: Jan 2007 Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on. Posts: 32175 Good Answers: 839	#7 In reply to #6 Re: Transformer Oil Testing 07/16/2013 11:48 AM
	£5GBP, then? __________________ "Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
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lyn Guru Join Date: Oct 2008 Posts: 42355 Good Answers: 1693	#8 In reply to #7 Re: Transformer Oil Testing 07/16/2013 11:56 AM
	You're betting on the OP?????
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pnaban Guru Join Date: Jun 2010 Location: srilanka Posts: 2725 Good Answers: 5	#10 In reply to #4 Re: Transformer Oil Testing 07/16/2013 11:17 PM
	What should be the breakdown voltage for various rated voltages of transformers for a test gap of 2.5mm?. __________________ pnaban
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electricalexpert65 Guru Join Date: Oct 2009 Posts: 2061 Good Answers: 169	#18 In reply to #10 Re: Transformer Oil Testing 07/18/2013 10:57 AM
	As per the Indian Standard IS 6792, the following should be the minimum breakdown values for insulating oils used on various rated voltages (across a test sphere gap of 2.5mm): 30kV (for use in equipment up to a rated voltage of 72.5kV) 40kV (for use in equipment for a rated voltage above 72.5kV to 170kV 50kV (for use in equipment for a rated voltage above 170kV)
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Shyam Guru Join Date: Aug 2006 Location: AM-51, Deen Dayal Nagar, Gwalior, Madhya Pradesh, MP 474001, India Posts: 3418 Good Answers: 32	#19 In reply to #18 Re: Transformer Oil Testing 07/18/2013 12:02 PM
	why 2.5mm was the original question? Why different ratings for testing? After all you can test the oil till it reaches breakdown voltage. Other simple method is to use a variable gap to see at which gap you get the breakdown for a fixed voltage. Why to fix a gap at all? 10kV at 1mm is as good as 100kV at 1cm. Just use a precision screw gap adjustment. __________________ Prof. (Dr.) Shyam, Managing Director for Sensors Technology Private Limited. Gwalior, MP474001, India.
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made ardian Participant Join Date: Feb 2018 Posts: 1	#21 In reply to #19 Re: Transformer Oil Testing 02/21/2018 8:51 AM
	Sir , can you explain with the formula how come to 2,5 mm ??
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Shyam Guru Join Date: Aug 2006 Location: AM-51, Deen Dayal Nagar, Gwalior, Madhya Pradesh, MP 474001, India Posts: 3418 Good Answers: 32	#9 Re: Transformer Oil Testing 07/16/2013 10:43 PM
	Electric field E = V/cm which is used for testing. You can change cm to mm to reduce the applied voltage by a factor of 10. In your case it will be 10/2.5 or factor of 4. Lower you go in distance, greater is the error in setting the gap but you do get an advantage of working at lower voltage. If you normally need 50kV/cm test voltage then you will need only 12.5kV for 2.5mm gap. Do you know the required electric field strength or breakdown voltage for the oil you are testing? __________________ Prof. (Dr.) Shyam, Managing Director for Sensors Technology Private Limited. Gwalior, MP474001, India.
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Pratik Trivedi Participant Join Date: Jul 2013 Posts: 2	#11 In reply to #9 Re: Transformer Oil Testing 07/16/2013 11:17 PM
	30 kv BDV is required to be maintained for this transformer.
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pnaban Guru Join Date: Jun 2010 Location: srilanka Posts: 2725 Good Answers: 5	#12 In reply to #11 Re: Transformer Oil Testing 07/16/2013 11:44 PM
	In 1960s I came to know it should be 10kV/mm but if rated voltage of transformer increases(say,1000kV in China) should it be the same?. Is there any regulation/code/standard which clearly states it?. __________________ pnaban
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Shyam Guru Join Date: Aug 2006 Location: AM-51, Deen Dayal Nagar, Gwalior, Madhya Pradesh, MP 474001, India Posts: 3418 Good Answers: 32	#13 In reply to #11 Re: Transformer Oil Testing 07/17/2013 12:14 AM
	15kV at 5mm discharge gap or even 30kV at 10mm discharge gap will be ideal for testing with current limited or current trip HV Supply of about 100uA or even less current. I often use 15kV HV Supply with maximum trip current of 500uA and normally trip at 100uA. As you are testing dielectric strength so you may have to go slightly extra for the margin. For 2.5mm gap actually you need 7.5kV or for 2mm gap you need 6kV. You can even use a spark plug for your bike to have fixed gap by measuring it accurately to 2mm spacing and try 6kV 500uA HV supply for testing. For larger gaps of 5mm, also you can try to pull the spark pin of the spark plug and use 15kV supply for testing. This will give much better results. I use those 6kV shown on the bottom side along with timers shown on the top. You can use any stable low noise low power HV DC Supply for this purpose. I have gate control BNC on the right right of the HV Supply which is used for enable disable the HV Supply. Trip current is internally preset. Some time you have just corona current and not continuous discharge so you can look at those waveform across a 1K ohms load resistor. 500uA * 1K will give 500mV across resistor if discharge is seen. make sure you connect load resistor towards ground terminal. I use five supplies at a time for quick testing but just one will do for you. If you need further help then write to me. __________________ Prof. (Dr.) Shyam, Managing Director for Sensors Technology Private Limited. Gwalior, MP474001, India.
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PeterT Guru Join Date: May 2010 Location: Liverpool, NY Posts: 961 Good Answers: 131	#16 In reply to #13 Re: Transformer Oil Testing 07/17/2013 1:34 PM
	Your test methods and parameters may have been acceptable in the past, but do not meet current ASTM or IEC transformer oil testing standards or methods. Other posters have given more accurate info. Based on the values you have quoted, the OP could end up with oil test results that you may have rated as "acceptable" but which wouldn't pass industry standard tests. I wouldn't recommend that he follow this approach! __________________ To get the right answers, first you need to ask the right questions.
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Shyam Guru Join Date: Aug 2006 Location: AM-51, Deen Dayal Nagar, Gwalior, Madhya Pradesh, MP 474001, India Posts: 3418 Good Answers: 32	#17 In reply to #16 Re: Transformer Oil Testing 07/17/2013 8:39 PM
	PeterT: Yes, the standards are tested as per the standards for the electrical equipment by the manufacturers and also by the repairer if it is refurbished. There is general requirement which you can call as other. Transformer oil quality of the running transformer to be tested if this needs immediate replacement or not. We have distribution lines of 33kV and 11kV and railways uses intermediate 25kV 50Hz single phase. Oil in all transformers degrade in time and economics sets the limit of the lowest tolerance level of the breakdown potential. It is well known that the oil will have micro corona discharges much higher in numbers with time and charge loss will increase and oil heating can be seen as increased temperature. Other than dielectric changes, there may be debris and gases and water and also polymer changing chemically over time. As far as our research is concern, we find the parameters of the current situation and long term usage defined in the application for the transformer oil in general. Transformer oil for us does not mean that it is only for transformers. It is a dielectric chemical material for very general electrical applications as insulator and perhaps as heat exchanging fluid. I think every engineer understands, that the standards are meant to be followed so that part is very obvious. Here, the person perhaps is learning to understand basics and Physics of basics is only electrical field E = V / D where is spark gap for applied voltage V. In my one research I needed to apply 50kV/mm voltage to 1mm thin LiF crystal to form Electrical Field 500kV/cm and obviously I need to fill the space by the transformer oil but above 100kV/mm the air bubbles of micro size caused corona discharges generating high energy UV from Nitrogen and Oxygen deeper electrons of above 10eV and this information was finally got stored in the LiF crystals as F-center defects. It was easy for me to read back these newly formed defects in numbers later on by thermally heating the crystal after removing the oil. Crystals gave intense light glow called Thermoluminescence. This became an indirect way of knowing or detecting micro corona discharges even if they were random as they could deposit information in the crystals of LiF. Scientific requirements take us to limits in testing and sometime we just do what is needed for the application. Transformer oil is also filled in many high voltage multiplier circuit we use and these circuits are meant to be used in table top instruments for several years and demand for testing these differs. Applied Killovolts UK also uses transformer oil in their HV Supplies (mini pulse transformers and voltage multipliers). Not all people are public distribution power transformer engineers. You are right in your own sense and I think that is the way electrical engineers must work as per book. I am a Physicist. __________________ Prof. (Dr.) Shyam, Managing Director for Sensors Technology Private Limited. Gwalior, MP474001, India.
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dhgrant

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#15
In reply to #11

Re: Transformer Oil Testing

07/17/2013 10:02 AM

Re: Transformer Oil Testing

There is a lot to the testing of transformer oil. There are many tests, although D1816 is one of the most important. I have written many very important tests for this critical fluid. Several of these tests have been accepted by international Standards Writing Organisations. If you can find IEEE, ASTM or IEC tests in a library, you need to read as many as you can find. If you can find them on line, read them and try to understand why they are needed. You may need to pay fees or join a technical group to read them online.

The right oil must be chosen first. There are basic specs for a new transformer oil, although some reclaimed, reprocessed oil will also meet those specs. When your oil arrives for your new transformer, you have to perform tests on it, and review the actual test data for the shipment before it left on its trip toward you. If the oil has not been contaminated on its trip, you will have to treat it to remove traces of air and water and any particles it picked up during its travel and tank transfers. After your transformer is vaccuum filled and is happily commissioned, you will have to make sure that its oil does not become contaminated in service. This is most likely when water leaks into it. The oil will also naturally degrade as oxygen combines with its hydrocarbon molecules. The same antioxidant, DBPC, that keeps your corn flakes and margarine from going rancid will also keep your transformer from becoming an acidic, tarry mess inside. You should specify an "inhibited" oil when you buy oil, and check every couple of years for the amount of DBPC left in the oil. The test I developed for DBPC assay by HPLC will detect it down to 100 or 150 ppm, which is so low that you really need to add some more. You cannot add pure crystals. Dissolve the DBPC in hot oil, cool it and add to the transformer to build it back to about 3000 ppm.

You should keep the water content of the oil below 20 ppm. You should perform the D1816 test on the oil every time you remove a liter of its oil for a full round of tests. We perform our tests at a 2mm gap between 'mushroom' shaped brass electrodes. Testers which use the flat disc electrodes will not protect you from bits of fiber floating in your oil. If you are using an older D877 type flat disc tester, you should upgrade. If your result is less than 30KV, your oil is not good. Water, and particles may now be floating around in it. You can only reduce the water content of oil by treating it to heat and vaccuum. You should look for a gasket leak or other problem if the water concentration in your oil is increasing.

Air naturally dissovles in oil while it is in service. With particles and dissovled water in the oil, this air will contribute to low BDV. You cannot keep the air or N2 blanketing gas from dissolving in the oil. Air wil naturally saturate the oil, at about 10 volume %. The best you can do is keep out water and particles. Fine particulate can also be formed by movement of internal components, as they 'micro-grind' against each other, due looseness and electro-mechanical forces. There should be no loose internal components in properly built transformer. This should be a warranty issue, if you can prove it to be a problem.

If your test results are low, you need to look at your test procedure. Resample. Compare the same oil tested for BDV by the same method at a different (accredited) oil lab. If the results are similar, your oil is bad. You will need to schedule an oil reclamation. This usually means draining the oil, cleaning it up, and vac reinstalling it. There are companies that specialize in cleaning oil without remvoing it, but too often this does not work. When the oil has been reclaimed properly and re-inhibited to 3000ppm DBPC, it should last a long time.

If freshly processed, the oil should be over 65KV with a 2mm gap. If you do no other test, the D1816 test will detect the most dangerous of problems. If having your transformer blow up, catch fire, or become a sludgy mess are OK with whoever owns it, and you get that in writing from them, then testing its oil thoroughly may not be 'your problem'. For the rest of us, having an oil test program set up by a competent professional is a cost-effective way to assure that your transform's life will be longer than yours or mine.

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Shyam Guru Join Date: Aug 2006 Location: AM-51, Deen Dayal Nagar, Gwalior, Madhya Pradesh, MP 474001, India Posts: 3418 Good Answers: 32	#20 In reply to #11 Re: Transformer Oil Testing 07/18/2013 12:30 PM
	30kV at 2.5mm or 120kV/cm? Then try 15kV at 1.25mm which is more safer to work. Working above 10kV normally poses lots of problems. As a rule of thumb we use 5mm / kV air gap in the instruments and at 30kV it will be 150mm or about 6 inches. if you use a coaxial cable then separate the insulation and top conductor 6 inches ahead of the hot wire center core. Keep the instrument properly grounded as any corona discharge in any direction going to do massive destruction so develop Faraday cage around everything to be protected. I use specially designed long insulated high voltage connectors and keep lots of free space around the hot conductor and preferably put multiple layers of rubber heat shrinking tubes to seal the conductor from air. If you do not seal the conductor and pass the 30kV then even at 6 inches above the conductor your hand can sense the current from free ions driving winds towards your hand and it feels cool even in hot summer. If you touch the 30kV DC of tester then you sure you won't be able to touch again. Remain very careful as ON/OFF switches can deceive you if you don't have discharge resistance and don't wait for capacitors holding deadly charge to discharge to a safe limit. Learn more about safety of working with HV, protection gears, and have some experienced person near you who knows the rules of HV operations. We never work single on HV hardware. Tell someone to turn off the power is something goes wrong. They person need to be alert and must stay near the mains switch. I bought a new spark plug for my bike to see the gap once more in the new one from Mico Bosch. It is of the first from left type with single ground pin folded over the hot pin. It looks like that it is only 1mm or perhaps slightly more than that but not 2mm for sure. In dry air 40kV/cm will easily fire thru so this must work on 4K-5kV range. I am going to see at what voltage in air it sparks here. Right now humidity is nearly 80%RH so breakdown voltage must be down. __________________ Prof. (Dr.) Shyam, Managing Director for Sensors Technology Private Limited. Gwalior, MP474001, India.
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kenergy Participant Join Date: Mar 2010 Location: NIGERIA Posts: 4	#14 Re: Transformer Oil Testing 07/17/2013 3:18 AM
	It is one of the standard in measuring the breakdown voltage of transformer oil.One can still use 2.0mm
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