TALKING TRANSFORMER TESTING
by Brenna ShumbamhiniJune 9, 2022
Condition monitoring is the frequent amassing, measuring, recording, and analysis of the relevant data relating to an asset’s operation. If we interpret the info correctly, it may give us great insight into the asset’s condition.
Frequent monitoring of the asset may end up in much less maintenance required or extra prolonged periods without any upkeep required.
It is essential to establish the key parameters which are wanted to provide us a whole picture of the actual status of the transformer and the motion we want to take to ensure the continued reliability of the asset to achieve the utmost lifetime.
What is the information telling us?
Has the situation of the unit changed since the final upkeep period?
Is it secure to function the unit?
Are there signs of deterioration?
Is it secure to load the unit above the nameplate score for a selected period?
Are we required to implement action to make sure the continued reliability of the unit?
How long can we use the unit earlier than we want to consider replacement?
Are the recognized problems of a recurring nature?
Effective situation monitoring outline
It is vitally necessary to determine clear goals as a part of your strategy. What do you want to obtain by implementing this situation monitoring plan? Is it in-service failure prevention? Or perhaps life extension? Maintenance deferral? By stipulating the result and what you need to accomplish, it will be much easier to determine the required parameters.
Health indexing of belongings is turning into a outstanding tool in getting a clearer image of the situation of your transformer. Test parameters carry a numerical value-adding to the whole value of the Health Index Value of the transformer. These parameter weight values had been calculated based mostly on the worldwide requirements for mineral oils, indicating the critical values stipulated within the varied standards.
The scope of oil analysis, interpretation of the data, and significant values
At the start of this section, it’s important to state that we deal with different dimension transformers in the industry. Transformers are divided into courses according to the kV rankings of the tools. It is up to the reliability or asset manager to use the guidelines for larger gear, thereby implementing shorter increment oil analysis and electrical exams.
The maintenance engineer or manager needs to determine what type of testing would profit him in figuring out downside areas inside his fleet. Some of the analysis has been recognized as to routine type checks. Still, there may be an extensive vary of checks that can assist in identifying particular downside criteria inside the system, which could not be clear via the standard day-to-day evaluation usually performed.
Please see the score courses in TABLE 1
TABLE 1 FIG
TABLE 2 explains which oil analyses are beneficial and the way usually or under which circumstances.
TABLE 2 FIG
The taking of the oil pattern is among the most vital and critical influencers in the evaluation consequence. If a pattern is not taken to the prescribed process, then there’s a vital chance that the analysis carried out, and the outcomes acquired, are of no use.
Care ought to be taken to ensure quality management procedures are applied in each step of the sampling course of as set out by international requirements. A good high quality sample taken by applying the proper procedure is important. A pattern may be contaminated by numerous factors, all of which might influence the result of the ends in a adverse method.
All steps concerned in pattern taking should adhere to quality control procedures, together with the container that is used, the sampling equipment, the taking of the pattern, the marking of the pattern, the closing of the sample, the storage and handling of the pattern, after which the supply of the sample to the laboratory.
If the pattern identification and pattern knowledge are handwritten, the human factor can result in incorrect interpretation of the data. The label ought to be stuck onto the container to ensure no mix-ups in sample identification. Ensure that the label is accomplished in neat, easy-to-read handwriting. The label ought to be waterproof, and the pen used to write down on the label ought to be oil- and waterproof. Otherwise, some knowledge might be misplaced, making it extremely difficult for the laboratory personnel to complete the report or allocate the pattern to a specific transformer.
Now, let’s discuss the kinds of checks to determine the transformer’s situation, the crucial values, and the beneficial actions in each case:
a) Colour and look
This is a routine inspection utilized to each oil sample.
When an oil sample arrives at the laboratory, one of many “tests” is a visual inspection of the oil pattern in a transparent vessel to discover out the color, turbidity, and possible particle identification.
Dark oils would possibly point out chemical degradation or contamination of the oil.
When there might be lots of turbidity, it’d point out a high water content material within the oil.
If the drain valve was not wiped clean by the sampler, the filth particles within the drain valve may be integrated into the sample. If particles are identified as carbon, it’d point out a attainable electrical fault within the unit. The DGA evaluation of the oil will confirm if that is so.
Clear oils with out contamination will indicate a great situation, and no action is really helpful.
When oils are dark or turbid, additional evaluation will verify any problems. The oil analysis outcomes will also decide the diploma and type of motion.
b) Breakdown Voltage
Breakdown Voltage (kV)O, A, D>6050 to 60<50
B, E>5040 to 50<40
C>4030 to 40<30
F<30 kV for OLTC in star level application<40 kV for OLTC in delta or line-end application
This is a routine inspection.
Breakdown voltage will point out the water content or the presence of international particles, or both in the oil being analysed.
As เกจวัดแรงดันดิจิตอล in transformers acts as an insulation medium to keep away from flashover within the unit, the breakdown voltage have to be excessive.
If the values are Good, it is strongly recommended to proceed with the present sample interval action plan.
If the values are Fair, more frequent sampling is recommended in collaboration with other parameter results just like the water content material, DDF (dielectric dissipation factor), and acidity.
If values are Poor – it is recommended to recondition the oil through oil reconditioning processes. If alternative tests indicate severe aging, the oil may be replaced with new or reclaimed oil. Another choice would be to perform on-site oil reclamation using a reclamation plant.
Reclamation of oil has the benefit that the colour of the oil is restored, and the polar parts are faraway from the oil. This course of removes acid and water in addition to some other compounds. Another advantage is that the oil can be re-used, and in most conditions, this may be accomplished without switching off the unit, which contributes to cost-saving. If unsure – as a substitute change off the unit throughout this therapy course of.
If the values are Poor, it is advisable to take action as soon as possible and never delay the upkeep process. Excess water within the transformer system decreases the projected transformer lifetime significantly; extraordinarily excessive water content can cause flashover in the unit, leading to loss of the asset.
c) Water content (mg/kg at transformer operating temperature)
Water Content(mg/kg at Transformer Operating Temperature)O, A<1515 to 20>20
B, D<2020 to 30>30
C, E<3030 to 40>40
FAction necessity >40
GNot a routine test
This is a routine test for all lessons of electrical equipment, except class G
The results of this test ought to always be considered along side the breakdown energy. If it is found that the water content material is high and the breakdown power is low, additional motion needs to be taken. It is really helpful that a second sample from the identical unit is examined to verify the results.
In the case of switching gear, the place there is no paper current, the breakdown voltage is the determining issue.
It must be famous that the limits indicated by IEC 60422 Edition 4 apply to transformers with operating temperatures between forty and 70 °C. If it is discovered that the unit’s working temperature is exterior this temperature range, it’s best to discuss with Annex A of the standard.
When the value obtained by way of analyses is GOOD, the normal sampling interval could be maintained, requiring no additional motion.
When the value returns a FAIR outcome, more frequent sampling is beneficial. It can be helpful to consider different parameters like the breakdown voltage, particle content material and DDF/resistivity, and acidity to resolve on the action to be implemented.
A POOR result would require quick action from the asset supervisor. This would possibly embody taking another sample to confirm the outcomes from the primary evaluation. If it is confirmed that the water content is high, the oil can be filtered; this process ought to remove a large portion of the moisture from the oil if applied appropriately. Follow-up samples have to be taken to make certain that the moisture content is still within the required limits. The reason is that probably the most significant portion of the water is caught up in the paper system within the transformer. This moisture will move from the paper into the oil beneath conditions that favour this motion. It could be discovered later that the oil in the water has elevated again with none apparent purpose, however the source can be the paper in the transformer.
A visual inspection can be really helpful to determine if any water would possibly transfer into the transformer or electrical gear via leaks. This problem might be extra extreme if the transformer or electrical equipment is outdoors and not in a coated space.
d) Acidity (mgKOH/g oil) Neutralization Number
Acidity mgKOH/g oilO, A, D<0.a hundred.10 to zero.15>0.15
B, E<0.100.10 to 0.25>0.20
C<0.a hundred.15 to 0.30>0.30
F, G Not a routine test
This is a routine take a look at for all courses besides F and G
The acids in oils are formed because of chemical reactions between the oil, water, and paper. Higher temperatures or load will increase will help within the formation of the acids. Because acids are polar compounds, it’s going to adversely affect the insulation properties of the oil and will improve paper degradation. If left untreated in transformers, this can result in sludge formation, usually around the lower components of the transformer core. The sludge will eventually type a semi-solid substance that’s extremely difficult to remove.
If the result is GOOD, the common sampling interval can proceed.
In case of a FAIR result, the sampling interval should be decreased to suit the state of affairs. Future evaluation ought to include a visible inspection of the oil for sediment and sludge.
If the result’s POOR according to the prescribed values in IEC 60422 Edition four.zero, the asset supervisor could determine to reclaim the oil or substitute it with new or reclaimed oil, whichever choice would possibly go properly with their requirements the most effective.
e) Dielectric Dissipation factor at 40Hz to 60Hz at 90° C
Dielectric Dissipation factorAt 40Hz to 60Hz at 90°CO, A<0.100.10 to 0.20>0.20
B, C<0.100.10 to zero.50>0.50
D<0.010.01 to zero.03>0.03
E<0.one hundred.01 to 0.30>0.03
F, GNot a routine take a look at
This is a routine check for all lessons of electrical tools, besides F and G
The dielectric dissipation factor or tan delta of this check provides information concerning the extent of the dielectric losses in transformer oil. This check measures the inefficiency of insulating materials.
When oil ages, we have the formation of polar compounds, resulting in section displacement and dielectric losses. Other impurities which may influence the dissipation issue include water, dissolved insulating resin, and paper.
When the result is FAIR, more frequent sampling and checking extra parameters is really helpful.
When the result’s POOR, reclamation or an oil change is recommended. The construction of the oil is damaged, in effect that the chemical bonds between the molecules have broken down, and even with filtration, the beneficial dielectric values can’t be achieved.
f) Resistivity (GΩm) at 20 °C or 90 °C
Resistivity(GΩm)At 20° CO, A>20020 to 200<20
B, C>604 to 60<4
D>800250 to 800<250
E>607 to 60<7
This is NOT a routine take a look at
DC resistivity of the oil is one of the key parameters to assess the transformer insulation situation; that is based mostly on the fact that DC resistance is sensitive to oil degradation.
When the result is FAIR, extra frequent sampling and checking additional parameters is recommended.
When the result’s POOR, reclamation or an oil change is recommended.
g) Inhibitor content material percent
Inhibitor Content %AllRestricted to Inhibited oils,Consult oil supplier40% to 60% Of unique value<40% of authentic value
This test is restricted to oils with this additive.
It would be advisable to contact the oil supplier to confirm the small print relating to additives.
The two most typical oxidation inhibitors for transformer oils are 2,6-di-tertiary-butyl para-cresol (DBPC) and 2,6-di-tertiary butyl-phenol (DBP). The function of the inhibitor is to forestall oxygen from reacting with the oil. This considerably slows the growing older process in the oil and the strong insulation.
If the result’s FAIR, it’s advised to top up the inhibitor level to the prescribed level per supplier directions. It is suggested to use a area skilled trained within the process to carry out this task.
If the result obtained is POOR, the recommendation for this state of affairs would suggest that the tip person continues to use the oil “uninhibited,” but this may lead to more speedy degradation of both the liquid and stable insulation.
It ought to be famous that some transformers already have a built-in oil preservation system; that is designed to maintain dissolved oxygen at levels beneath 1000ppm. This would be within the form of a nitrogen system, a nitrogen tank or generator, or a conservator tank outfitted with a rubber diaphragm (bladder). Using inhibited oils under these circumstances is not required, although it might add additional safety towards oil oxidation if the preservation system ever fails. 
h) Passivator content
Passivator Content (mg/kg)O,A,B,C,D,E,F.>70 and secure, (rate of decrease < 10/mg/kg/year)50-70mg/kg or<70mg/kg, with a significantrate of lower of >10mg/kg/year<50 and decreasing at >10mg/kg/year
Passivators, also called steel deactivators, react with reactive steel surfaces and dissolved metals corresponding to copper and silver and cut back their rate of reaction with compounds within the oil. This consists of oxidation reactions with organic compounds and reactions with corrosive sulfur. Passivators are composed of two basic sorts, sulfur-based and nitrogen-based. The first suggested use of passivators in transformer oil, of which the author is conscious, was in 1967 by J.J. Melchiore and I.W. Mills of the Sun Oil Company.
As the oil ages, the passivator may deplete more quickly; this depletion might speed up when the oil is un-inhibited.
With GOOD results, common sample intervals may be maintained.
With FAIR outcomes, preserve regular monitoring.
When POOR, it’s advised to take away the oil or take away the source of corrosivity from the oil through special oil therapy.
I) Sediment and sludge
This just isn’t a routine test.
It is suggested that this check is performed when the oil results indicate a excessive acid worth and the dissipation issue is close to the unacceptable restrict.
The outcomes need to be less than 0.02% by mass to be negligible. If the outcomes return a worth of greater than zero.02% by mass, it’s suggested that or not it’s reclaimed; in any other case, an oil change is really helpful.
j) Interfacial tension
This is not a routine take a look at
Interfacial Tension (mN/m)O, A, B, C, DInhibited Uninhibited>28 >2522 to twenty-eight 20 to 25<22 <20
ENot a routine test
F, GNot Applicable
The interfacial rigidity between transformer oil and water reduces in the course of the growing older process. What this means in practical terms is there is extra polar compound current within the oil, lowering the flexibility of an oil to serve as an insulator within the transformer system. There is a direct correlation between interfacial tension and neutralisation quantity. Therefore, the interfacial rigidity turns into a quality criterion: the oil have to be modified under a predefined limit.
If outcomes are GOOD, proceed the regular sampling interval.
If results are FAIR, lower the sampling interval.
If results are POOR, check the oil for sediment and/or sludge.
k) Corrosive sulfur
This is not a routine take a look at.
Oil is either corrosive or non-corrosive.
The presence of corrosive sulfur in transformer oil and its effect on the transformer system may be important. The extent of the corrosion damage caused by the sulfur can be so severe that it’d trigger failure of the equipment if not checked. The addition of a copper passivator can reduce the impression of this compound on the transformer system.
In a study by Doble, it has been discovered that rubber products utilized in transformers would possibly add to the corrosivity of the oil. Nitrile rubber gaskets and hoses not approved for oil filtration might contaminate the oil with corrosive sulfur.
CIGRE Brochure no 378, 2009 stipulates the need of corrective actions primarily based on this institute’s threat evaluation study. 
l) Particle counting and sizing
Table three: Particles
Table B.1 – Typical contamination ranges (particles) encountered on power transformer insulating oil as measured utilizing IEC 60970 
m) Flashpoint ° C
Not a routine test
If there’s a most lower in flashpoints by 10%, the equipment might require additional inspection. This value may differ in different nations.
It is suggested to carry out this check when an unusual odour is observed, the unit has been refilled, or an inner fault has occurred.
n) PCB (Polychlorinated Biphenyls)
This take a look at is not to determine the situation of the transformer; this could be a health and security impression check. PCB is hazardous to each humans and the surroundings; it’s critical to check for PCBs after the retro fill of a transformer. It is also required whenever any maintenance has been done on the unit, and the potential of contamination is present. If PCB content material exceeds the really helpful limits, the appropriate action must be taken.
Units with a PCB content of more than 50ppm require a hearth safety plan, environmental safety plan, and additional precautionary measures when maintenance is completed. This oil needs to be changed, and the oil disposed of as hazardous waste, with a certificates of protected disposal issued to the tools proprietor.
Local regulatory bodies define the boundaries.
o) DGA (Dissolved Gas Analysis)
As DGA is an intricate science with a lot of data and interpretation, we’ll focus on this phenomenon partially II of the article. The limits for the different gases and the interpretation of this knowledge according to international standards shall be mentioned intimately, forming a part of the overall well being score willpower of the transformer.
Transformer condition monitoring is an interlaced, highly thrilling area of study. In this article, we centered on the types of tests to find out the condition of the transformer, the critical values, and the really helpful actions.
The Health Index indication makes it possible to see the supposed reliability of a specific unit at a particular date and time. This makes it attainable to ensure finest practice utility and optimised maintenance. It additionally make it simpler to draw up a upkeep plan and action plan.
1. IEC 60422 Edition four.0 2013-01 International Standard (Mineral insulating oils in electrical tools – supervision and upkeep guide)
2. Oxidation inhibitor and reinhabiting oil-filled transformers, by Andy Shkolnik
three. Passivators, what they are and the way they work, by Lance Lewand, Doble Engineering Company.
four. CIGRE technical brochure 378, 2009 “Copper sulfide in Transformer Insulation.”
5. CIGRE Technical Brochure 157, 2000 “Effect of particles on transformer dielectric energy.”
6. Article initially revealed by Transformer Technology Magazine Issue 16 – December 2021 https://www.transformer-technology.com
Corné Dames is a WearCheck transformer consultant. She has 20+ years’ expertise in the trade, having previously labored as laboratory manager for a major industrial laboratory group, focusing on transformer well being. She has been intrigued by transformer chemistry proper from the start of her career, particularly within the analysis of test information. Corné has huge practical and theoretical information of reliability upkeep programmes.
Water hammer could be a main concern in pumping techniques and should be a consideration for designers for a quantity of reasons. If not addressed, it can cause a number