by Brenna ShumbamhiniJune 9, 2022
Corne Dames
Condition monitoring is the frequent amassing, measuring, recording, and analysis of the related information concerning an asset’s operation. If we interpret the information correctly, it can give us nice perception into the asset’s situation.
Frequent monitoring of the asset can outcome in less upkeep required or extra extended intervals without any maintenance required.
It is crucial to establish the necessary thing parameters that are needed to offer us a complete image of the actual standing of the transformer and the motion we need to take to make sure the continued reliability of the asset to achieve the utmost lifetime.
What is the info telling us?
Has the condition of the unit modified since the last upkeep period?
Is it secure to function the unit?
Are there signs of deterioration?
Is it protected to load the unit above the nameplate ranking for a specific period?
Are we required to implement action to ensure the continued reliability of the unit?
How long can we use the unit before we have to contemplate replacement?
Are the recognized issues of a recurring nature?
Effective situation monitoring outline
It is vitally essential to establish clear goals as a part of your technique. What do you need to obtain by implementing this condition monitoring plan? Is it in-service failure prevention? Or perhaps life extension? Maintenance deferral? By stipulating the outcome and what you need to accomplish, it will be a lot simpler to establish the required parameters.
Health indexing of property is becoming a outstanding software in getting a clearer image of the situation of your transformer. Test parameters carry a numerical value-adding to the total value of the Health Index Value of the transformer. These parameter weight values were calculated primarily based on the worldwide standards for mineral oils, indicating the crucial values stipulated in the varied standards.
The scope of oil evaluation, interpretation of the data, and critical values
At the beginning of this part, it’s important to state that we cope with completely different dimension transformers in the trade. Transformers are divided into classes based on the kV ratings of the tools. It is as much as the reliability or asset supervisor to use the rules for bigger equipment, thereby implementing shorter increment oil analysis and electrical tests.
The maintenance engineer or manager needs to discover out what type of testing would benefit him in identifying drawback areas within his fleet. Some of the evaluation has been recognized as to routine type exams. Still, there is an intensive range of checks that may help in figuring out particular drawback criteria within the system, which might not be clear via the typical day-to-day analysis usually carried out.
Please see the ranking courses in TABLE 1
TABLE 2 explains which oil analyses are recommended and how often or beneath which circumstances.
Oil sampling
The taking of the oil pattern is considered one of the most crucial and important influencers within the evaluation outcome. If a pattern is not taken to the prescribed procedure, then there’s a vital chance that the evaluation performed, and the outcomes acquired, are of no use.
Care must be taken to make sure high quality management procedures are applied in each step of the sampling process as set out by international requirements. เกจวัดแรงดันน้ำไทวัสดุ taken by making use of the correct process is essential. A pattern could be contaminated by numerous factors, all of which can affect the finish result of the leads to a unfavorable manner.
All steps concerned in sample taking should adhere to high quality management procedures, including the container that’s used, the sampling equipment, the taking of the pattern, the marking of the pattern, the closing of the pattern, the storage and dealing with of the pattern, and then the delivery of the sample to the laboratory.
If the pattern identification and pattern information are handwritten, the human factor can lead to incorrect interpretation of the info. The label should be caught onto the container to ensure no mix-ups in pattern identification. Ensure that the label is accomplished in neat, easy-to-read handwriting. The label must be waterproof, and the pen used to write down on the label should be oil- and water resistant. Otherwise, some information might be misplaced, making it extremely troublesome for the laboratory personnel to complete the report or allocate the sample to a selected transformer.
Now, let’s talk about the kinds of tests to discover out the transformer’s condition, the critical values, and the beneficial actions in every case:
a) Colour and look
This is a routine inspection utilized to every oil pattern.
When an oil pattern arrives at the laboratory, one of many “tests” is a visual inspection of the oil pattern in a transparent vessel to find out the colour, turbidity, and possible particle identification.
Dark oils may point out chemical degradation or contamination of the oil.
When there may be plenty of turbidity, it would indicate a excessive water content in the oil.
If the drain valve was not cleaned by the sampler, the filth particles in the drain valve may be incorporated into the sample. If particles are identified as carbon, it’d indicate a potential electrical fault within the unit. The DGA evaluation of the oil will verify if so.
Clear oils with out contamination will point out an excellent condition, and no action is really helpful.
When oils are darkish or turbid, additional analysis will confirm any problems. The oil evaluation outcomes may also determine the diploma and sort 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 point application<40 kV for OLTC in delta or line-end utility
G <30
This is a routine inspection.
Breakdown voltage will point out the water content or the presence of international particles, or each in the oil being analysed.
As pressure gauge digital ราคา in transformers acts as an insulation medium to keep away from flashover in the unit, the breakdown voltage should be excessive.
If the values are Good, it is recommended to continue with the present sample interval motion plan.
If the values are Fair, extra frequent sampling is beneficial in collaboration with different parameter results like the water content, DDF (dielectric dissipation factor), and acidity.
If values are Poor – it is recommended to recondition the oil by way of oil reconditioning processes. If different checks point out severe aging, the oil may be replaced with new or reclaimed oil. Another option could be to carry out on-site oil reclamation using a reclamation plant.
Reclamation of oil has the benefit that the color of the oil is restored, and the polar elements are removed from the oil. This course of removes acid and water as well as some other compounds. Another advantage is that the oil can be re-used, and in most conditions, this could be done with out switching off the unit, which contributes to cost-saving. If doubtful – as a substitute swap off the unit throughout this therapy course of.
If the values are Poor, it’s advisable to take motion as quickly as attainable and never delay the upkeep process. Excess water in the transformer system decreases the projected transformer lifetime considerably; extremely excessive water content may cause flashover within the unit, resulting in loss of the asset.
c) Water content material (mg/kg at transformer working 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 check for all classes of electrical gear, besides class G
The results of this test should always be considered at the facet of the breakdown energy. If it’s found that the water content is high and the breakdown strength is low, further action must be taken. It is beneficial that a second pattern from the same unit is examined to substantiate the outcomes.
In the case of switching equipment, the place there is not any paper current, the breakdown voltage is the figuring out issue.
It ought to be famous that the bounds indicated by IEC 60422 Edition 4 apply to transformers with operating temperatures between forty and 70 °C. If it’s found that the unit’s working temperature is outdoors this temperature vary, it’s best to refer to Annex A of the usual.
When the value obtained by way of analyses is GOOD, the normal sampling interval can be maintained, requiring no further motion.
When the value returns a FAIR result, extra frequent sampling is beneficial. It can also be useful to think about other parameters just like the breakdown voltage, particle content material and DDF/resistivity, and acidity to determine on the action to be applied.
A POOR end result would require quick action from the asset supervisor. This might embrace taking one other pattern to substantiate the results from the primary evaluation. If it is confirmed that the water content material is high, the oil could be filtered; this process ought to take away a large portion of the moisture from the oil if applied appropriately. Follow-up samples must be taken to make sure that the moisture content is still within the required limits. The reason is that essentially the most significant portion of the water is caught up within the paper system in the transformer. This moisture will move from the paper into the oil beneath circumstances that favour this motion. It could be found later that the oil in the water has elevated again without any apparent cause, but the source can be the paper in the transformer.
A visible inspection is also beneficial to determine if any water would possibly move into the transformer or electrical tools by way of leaks. This drawback could be extra severe if the transformer or electrical equipment is outside and not in a coated space.
d) Acidity (mgKOH/g oil) Neutralization Number
Acidity mgKOH/g oilO, A, D<0.a hundred.10 to 0.15>0.15
B, E<0.a hundred.10 to zero.25>0.20
C<0.100.15 to 0.30>0.30
F, G Not a routine test
This is a routine test for all lessons besides F and G
The acids in oils are formed as a outcome of chemical reactions between the oil, water, and paper. Higher temperatures or load will increase will assist within the formation of the acids. Because acids are polar compounds, it will adversely have an result on the insulation properties of the oil and will improve paper degradation. If left untreated in transformers, this could lead to sludge formation, often around the decrease components of the transformer core. The sludge will finally type a semi-solid substance that is extremely difficult to remove.
If the result’s GOOD, the common sampling interval can proceed.
In case of a FAIR outcome, the sampling interval must be decreased to suit the state of affairs. Future analysis ought to embrace a visual inspection of the oil for sediment and sludge.
If the result’s POOR based on the prescribed values in IEC 60422 Edition, the asset manager might resolve to reclaim the oil or replace it with new or reclaimed oil, whichever option might go well 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.a hundred.10 to zero.20>0.20
B, C< hundred.10 to zero.50>0.50
D<0.010.01 to 0.03>0.03
E<0.100.01 to 0.30>0.03
F, GNot a routine check
This is a routine check for all classes of electrical tools, except F and G
The dielectric dissipation issue or tan delta of this take a look at offers information relating to the extent of the dielectric losses in transformer oil. This test measures the inefficiency of insulating material.
When oil ages, we have the formation of polar compounds, leading to part displacement and dielectric losses. Other impurities which may influence the dissipation factor embody water, dissolved insulating resin, and paper.
When the result is FAIR, more frequent sampling and checking extra parameters is beneficial.
When the result is POOR, reclamation or an oil change is recommended. The structure of the oil is damaged, in impact that the chemical bonds between the molecules have damaged down, and even with filtration, the really helpful dielectric values can’t be achieved.
f) Resistivity (GΩm) at 20 °C or ninety °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 test
DC resistivity of the oil is amongst the key parameters to evaluate the transformer insulation condition; that is based on the reality that DC resistance is delicate to grease degradation.
When the result’s FAIR, more frequent sampling and checking extra parameters is recommended.
When the result is POOR, reclamation or an oil change is really helpful.
g) Inhibitor content material percent
Inhibitor Content %AllRestricted to Inhibited oils,Consult oil supplier40% to 60% Of authentic value<40% of authentic value
This test is restricted to oils with this additive.
It would be advisable to contact the oil supplier to verify the small print relating to components.
The two most common 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 prevent oxygen from reacting with the oil. This considerably slows the aging process in the oil and the stable insulation.
If the result’s FAIR, it’s suggested to top up the inhibitor stage to the prescribed degree per supplier instructions. It is advised to make use of a field professional trained in the process to carry out this process.
If the outcome obtained is POOR, the recommendation for this scenario would counsel that the end user continues to use the oil “uninhibited,” however this will result in more rapid degradation of both the liquid and solid insulation.
It should be noted that some transformers have already got a built-in oil preservation system; this is designed to maintain dissolved oxygen at ranges beneath 1000ppm. This can be in the form of a nitrogen system, a nitrogen tank or generator, or a conservator tank outfitted with a rubber diaphragm (bladder). Using inhibited oils beneath these circumstances isn’t required, although it would add extra safety against oil oxidation if the preservation system ever fails. [2]
h) Passivator content material
Passivator Content (mg/kg)O,A,B,C,D,E,F.>70 and stable, (rate of lower < 10/mg/kg/year)50-70mg/kg or<70mg/kg, with a significantrate of lower of >10mg/kg/year<50 and lowering at >10mg/kg/year
Passivators, also recognized as metal deactivators, react with reactive metal surfaces and dissolved metals such as copper and silver and scale back their price of reaction with compounds in the oil. This consists of oxidation reactions with organic compounds and reactions with corrosive sulfur. Passivators are composed of two primary varieties, sulfur-based and nitrogen-based. The first suggested use of passivators in transformer oil, of which the creator is aware, was in 1967 by J.J. Melchiore and I.W. Mills of the Sun Oil Company.[3]
As the oil ages, the passivator would possibly deplete extra quickly; this depletion would possibly speed up when the oil is un-inhibited.
With GOOD results, regular sample intervals could be maintained.
With FAIR results, maintain common monitoring.
When POOR, it’s advised to take away the oil or remove the supply of corrosivity from the oil via special oil remedy.
I) Sediment and sludge
This just isn’t a routine test.
It is advised that this check is performed when the oil outcomes point out a high acid worth and the dissipation factor is near the unacceptable restrict.
The outcomes have to be lower than zero.02% by mass to be negligible. If the outcomes return a price of greater than zero.02% by mass, it is advised that it be reclaimed; otherwise, an oil change is beneficial.
j) Interfacial rigidity
This isn’t a routine check
Interfacial Tension (mN/m)O, A, B, C, DInhibited Uninhibited>28 >2522 to twenty-eight 20 to 25<22 <20
ENot a routine check
F, GNot Applicable
The interfacial rigidity between transformer oil and water reduces during the getting older process. What this means in sensible terms is there could be extra polar compound present within the oil, reducing the power of an oil to function an insulator in the transformer system. There is a direct correlation between interfacial rigidity and neutralisation quantity. Therefore, the interfacial pressure becomes a high quality criterion: the oil have to be modified below a predefined limit.
If outcomes are GOOD, continue the common sampling interval.
If results are FAIR, lower the sampling interval.
If outcomes are POOR, check the oil for sediment and/or sludge.
k) Corrosive sulfur
This isn’t a routine test.
Oil is both corrosive or non-corrosive.
The presence of corrosive sulfur in transformer oil and its impact on the transformer system may be vital. The extent of the corrosion injury attributable to the sulfur may be so severe that it might trigger failure of the tools if not checked. The addition of a copper passivator can cut back the influence of this compound on the transformer system.
In a examine by Doble, it has been found that rubber merchandise utilized in transformers might add to the corrosivity of the oil. Nitrile rubber gaskets and hoses not permitted for oil filtration would possibly contaminate the oil with corrosive sulfur.
CIGRE Brochure no 378, 2009 stipulates the need of corrective actions primarily based on this institute’s threat assessment study. [4]
l) Particle counting and sizing
Table three: Particles
Table B.1 – Typical contamination levels (particles) encountered on energy transformer insulating oil as measured using IEC 60970 [5]
m) Flashpoint ° C
Not a routine check
If there is a maximum lower in flashpoints by 10%, the equipment might require additional inspection. This worth might differ in different nations.
It is suggested to perform this test when an uncommon odour is observed, the unit has been refilled, or an inner fault has occurred.
n) PCB (Polychlorinated Biphenyls)
This check is to not determine the condition of the transformer; it is a well being and safety impression test. PCB is hazardous to both people and the surroundings; it is important to check for PCBs after the retro fill of a transformer. It can also be required every time any maintenance has been carried out on the unit, and the chance of contamination is current. If PCB content exceeds the recommended limits, the appropriate action needs to be taken.
Units with a PCB content material of more than 50ppm require a hearth security plan, environmental protection plan, and additional precautionary measures when maintenance is finished. This oil needs to be replaced, and the oil disposed of as hazardous waste, with a certificate of protected disposal issued to the tools proprietor.
Local regulatory bodies outline the bounds.
o) DGA (Dissolved Gas Analysis)
As DGA is an intricate science with plenty of data and interpretation, we’ll focus on this phenomenon in part II of the article. The limits for the different gases and the interpretation of this information based on worldwide requirements might be discussed in detail, forming part of the overall well being rating willpower of the transformer.
Transformer condition monitoring is an interlaced, highly exciting field of examine. In this text, we targeted on the kinds of checks to determine the condition of the transformer, the important values, and the really helpful actions.
The Health Index indication makes it attainable to see the supposed reliability of a selected unit at a specific date and time. This makes it potential to make sure best practice software and optimised maintenance. It also make it easier to draw up a upkeep plan and motion plan.
1. IEC 60422 Edition 4.0 2013-01 International Standard (Mineral insulating oils in electrical gear – supervision and maintenance guide)
2. Oxidation inhibitor and reinhabiting oil-filled transformers, by Andy Shkolnik
three. Passivators, what they’re and how they work, by Lance Lewand, Doble Engineering Company.
4. CIGRE technical brochure 378, 2009 “Copper sulfide in Transformer Insulation.”
5. CIGRE Technical Brochure 157, 2000 “Effect of particles on transformer dielectric power.”
6. Article initially published by Transformer Technology Magazine Issue 16 – December 2021
Author bio:
Corné Dames is a WearCheck transformer consultant. She has 20+ years’ experience within the trade, having beforehand labored as laboratory manager for a significant industrial laboratory group, specializing in transformer well being. She has been intrigued by transformer chemistry proper from the start of her career, particularly in the evaluation of check data. Corné has vast sensible and theoretical data of reliability maintenance programmes.

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