PETROL CHEMICALS
TALKING TRANSFORMER TESTING
by Brenna ShumbamhiniJune 9, 2022
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Introduction
Corne Dames
Condition monitoring is the frequent collecting, measuring, recording, and evaluation of the relevant knowledge concerning an asset’s operation. If we interpret the information appropriately, it can provide us nice perception into the asset’s situation.
Frequent monitoring of the asset can outcome in much less maintenance required or extra extended intervals with none maintenance required.
It is crucial to identify the important thing parameters which are needed to provide us a complete image of the particular status of the transformer and the motion we want to take to make sure the continued reliability of the asset to achieve the maximum lifetime.
What is the data telling us?
Has the condition of the unit changed because the last upkeep period?
Is it protected to function the unit?
Are there signs of deterioration?
Is it safe to load the unit above the nameplate score for a specific period?
Are we required to implement motion to ensure the continued reliability of the unit?
How lengthy can we use the unit before we have to consider replacement?
Are the identified problems of a recurring nature?
Effective condition monitoring define
It is vitally important to identify clear goals as part of your strategy. What do you wish to achieve 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 want to accomplish, it will be much simpler to determine the required parameters.
Health indexing of belongings is turning into a outstanding device 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 have been calculated based mostly on the worldwide standards for mineral oils, indicating the critical values stipulated in the numerous standards.
The scope of oil analysis, interpretation of the information, and important values
At the start of this part, it is essential to state that we deal with totally different size transformers within the industry. Transformers are divided into lessons based on the kV rankings of the gear. It is as a lot as the reliability or asset supervisor to make use of the rules for bigger equipment, thereby implementing shorter increment oil analysis and electrical checks.
The maintenance engineer or manager wants to determine what kind of testing would benefit him in identifying drawback areas within his fleet. Some of the evaluation has been identified as to routine type checks. Still, there might be an in depth range of tests that may assist in identifying particular downside criteria within the system, which could not be clear through the typical day-to-day evaluation normally carried out.
Please see the ranking classes in TABLE 1
TABLE 1 FIG
TABLE 2 explains which oil analyses are beneficial and how often or underneath which circumstances.
TABLE 2 FIG
Oil sampling
The taking of the oil pattern is one of the most crucial and significant influencers in the analysis end result. If a pattern just isn’t taken to the prescribed process, then there’s a important risk that the analysis carried out, and the results acquired, are of no use.
Care should be taken to make sure quality management procedures are applied in each step of the sampling process as set out by worldwide standards. A good quality pattern taken by making use of the right procedure is essential. A pattern could be contaminated by various elements, all of which can influence the end result of the leads to a unfavorable manner.
All steps involved in sample taking must adhere to high quality management procedures, together with the container that is used, the sampling package, the taking of the sample, the marking of the pattern, the closing of the sample, the storage and dealing with of the pattern, and then the supply of the pattern to the laboratory.
If the pattern identification and pattern data are handwritten, the human issue can lead to incorrect interpretation of the info. The label ought to be caught onto the container to ensure no mix-ups in pattern identification. Ensure that the label is completed in neat, easy-to-read handwriting. The label ought to be waterproof, and the pen used to put in writing on the label should be oil- and water-resistant. Otherwise, some knowledge may be lost, making it extraordinarily tough for the laboratory personnel to complete the report or allocate the sample to a selected transformer.
Now, let’s discuss the kinds of exams to determine the transformer’s situation, the critical values, and the recommended actions in every case:
a) Colour and appearance
This is a routine inspection utilized to each oil pattern.
When an oil pattern arrives at the laboratory, one of the “tests” is a visual inspection of the oil sample in a clear vessel to determine the colour, turbidity, and attainable particle identification.
Dark oils may indicate chemical degradation or contamination of the oil.
When there is a lot of turbidity, it would point out a excessive water content material in the oil.
If the drain valve was not cleaned by the sampler, the dust particles in the drain valve may be integrated into the sample. If particles are identified as carbon, it’d point out a possible electrical fault in the unit. The DGA evaluation of the oil will confirm if so.
Clear oils with out contamination will indicate a great situation, and no motion is recommended.
When oils are dark or turbid, further analysis will verify any problems. The oil evaluation outcomes may even determine the diploma and kind of motion.
b) Breakdown Voltage
PropertyCategoryGoodFairPoor
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 utility
G <30
This is a routine inspection.
Breakdown voltage will point out the water content material or the presence of overseas particles, or each in the oil being analysed.
As the oil in transformers acts as an insulation medium to keep away from flashover within the unit, the breakdown voltage should be excessive.
If the values are Good, it is suggested to proceed with the current sample interval action plan.
If the values are Fair, extra frequent sampling is recommended in collaboration with different 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 checks indicate severe getting older, the oil can be replaced with new or reclaimed oil. Another choice would be to carry out on-site oil reclamation utilizing a reclamation plant.
Reclamation of oil has the advantage that the color of the oil is restored, and the polar elements are faraway from the oil. This process removes acid and water in addition to another compounds. Another benefit is that the oil may be re-used, and in most situations, this could be accomplished with out switching off the unit, which contributes to cost-saving. If doubtful – instead change off the unit during this treatment process.
If the values are Poor, it is advisable to take motion as quickly as potential and never delay the maintenance course of. Excess water within the transformer system decreases the projected transformer lifetime considerably; extraordinarily excessive water content may cause flashover in the unit, leading to loss of the asset.
c) Water content material (mg/kg at transformer operating temperature)
PropertyCategoryGoodFairPoor
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 courses of electrical equipment, besides class G
The outcomes of this take a look at ought to always be thought of in conjunction with the breakdown strength. If it is found that the water content material is high and the breakdown strength is low, further motion must be taken. It is really helpful that a second pattern from the identical unit is examined to confirm the outcomes.
In the case of switching equipment, where there is not any paper current, the breakdown voltage is the figuring out issue.
It ought to be noted that the boundaries indicated by IEC 60422 Edition four apply to transformers with working temperatures between forty and 70 °C. If it is found that the unit’s operating temperature is outside this temperature range, it’s best to check with Annex A of the usual.
When the worth obtained by way of analyses is GOOD, the traditional sampling interval can be maintained, requiring no further motion.
When the value returns a FAIR end result, extra frequent sampling is really helpful. It is also helpful to assume about other parameters just like the breakdown voltage, particle content material and DDF/resistivity, and acidity to determine on the motion to be implemented.
A POOR end result would require instant action from the asset manager. This may embody taking another pattern to verify the results from the first analysis. If เกจวัดแรงดันแก๊สอาร์กอน is confirmed that the water content is excessive, the oil could be filtered; this course of ought to take away a big portion of the moisture from the oil if applied correctly. Follow-up samples have to be taken to ensure that the moisture content continues to be within the required limits. The purpose is that the most good portion of the water is caught up within the paper system in the transformer. pressure gauge ด้าน ดูด will transfer from the paper into the oil beneath conditions that favour this motion. It could be found later that the oil within the water has elevated once more with none apparent purpose, however the supply would be the paper within the transformer.
A visible inspection can additionally be recommended to determine if any water would possibly move into the transformer or electrical gear via leaks. This problem may be extra severe if the transformer or electrical gear is outdoors and not in a covered space.
d) Acidity (mgKOH/g oil) Neutralization Number
PropertyCategoryGoodFairPoor
Acidity mgKOH/g oilO, A, D<0.100.10 to zero.15>0.15
B, E<0.100.10 to zero.25>0.20
C<0.one hundred.15 to 0.30>0.30
F, G Not a routine take a look at
This is a routine check for all classes except F and G
The acids in oils are fashioned due to 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 will adversely affect the insulation properties of the oil and will improve paper degradation. If left untreated in transformers, this can lead to sludge formation, often across the lower parts of the transformer core. The sludge will eventually type a semi-solid substance that is extraordinarily difficult to remove.
If the result is GOOD, the common sampling interval can proceed.
In case of a FAIR outcome, the sampling interval must be decreased to fit the situation. Future analysis should embrace a visible inspection of the oil for sediment and sludge.
If the result’s POOR in accordance with the prescribed values in IEC 60422 Edition four.0, the asset manager might determine to reclaim the oil or replace it with new or reclaimed oil, whichever possibility may swimsuit their requirements the best.
e) Dielectric Dissipation issue at 40Hz to 60Hz at 90° C
PropertyCategoryGoodFairPoor
Dielectric Dissipation factorAt 40Hz to 60Hz at 90°CO, A<0.one hundred.10 to zero.20>0.20
B, C<0.100.10 to zero.50>0.50
D<0.010.01 to zero.03>0.03
E<0.a hundred.01 to 0.30>0.03
F, GNot a routine take a look at
This is a routine take a look at for all lessons of electrical tools, except F and G
The dielectric dissipation factor or tan delta of this check provides information regarding the extent of the dielectric losses in transformer oil. This check measures the inefficiency of insulating materials.
When oil ages, we’ve the formation of polar compounds, resulting in section displacement and dielectric losses. Other impurities which may affect 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’s POOR, reclamation or an oil change is beneficial. The structure of the oil is broken, 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 90 °C
PropertyCategoryGoodFairPoor
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; this is based mostly on the reality that DC resistance is sensitive to grease degradation.
When the result is FAIR, more frequent sampling and checking further parameters is beneficial.
When the result is POOR, reclamation or an oil change is recommended.
g) Inhibitor content %
PropertyCategoryGoodFairPoor
Inhibitor Content %AllRestricted to Inhibited oils,Consult oil supplier40% to 60% Of original value<40% of unique worth
This check is restricted to oils with this additive.
It can be advisable to contact the oil provider to verify the primary points concerning components.
The two commonest oxidation inhibitors for transformer oils are 2,6-di-tertiary-butyl para-cresol (DBPC) and a pair of,6-di-tertiary butyl-phenol (DBP). The purpose of the inhibitor is to stop oxygen from reacting with the oil. This considerably slows the aging course of within the oil and the solid insulation.
If the result’s FAIR, it is advised to prime up the inhibitor level to the prescribed level per supplier instructions. It is suggested to make use of a subject skilled skilled in the procedure to perform this task.
If the outcome obtained is POOR, the advice for this situation would suggest that the top consumer continues to make use of the oil “uninhibited,” however this will lead to more rapid degradation of both the liquid and solid insulation.
It must be noted that some transformers have already got a built-in oil preservation system; that is designed to keep dissolved oxygen at ranges below 1000ppm. This could be within the form of a nitrogen system, a nitrogen tank or generator, or a conservator tank equipped with a rubber diaphragm (bladder). Using inhibited oils underneath these circumstances isn’t required, although it might add extra safety towards oil oxidation if the preservation system ever fails. [2]
h) Passivator content material
PropertyCategoryGoodFairPoor
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 lowering at >10mg/kg/year
Passivators, also known as metallic deactivators, react with reactive metallic surfaces and dissolved metals similar to copper and silver and scale back their rate of reaction with compounds in the oil. This consists of oxidation reactions with natural compounds and reactions with corrosive sulfur. Passivators are composed of two primary types, sulfur-based and nitrogen-based. The first instructed use of passivators in transformer oil, of which the author 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 may deplete extra rapidly; this depletion may speed up when the oil is un-inhibited.
With GOOD results, regular sample intervals can be maintained.
With FAIR results, preserve regular monitoring.
When POOR, it is suggested to take away the oil or take away the source of corrosivity from the oil via particular oil remedy.
I) Sediment and sludge
This isn’t a routine test.
It is suggested that this take a look at is performed when the oil outcomes point out a excessive acid value and the dissipation factor is near the unacceptable limit.
The results have to be lower than zero.02% by mass to be negligible. If the results return a price of more than 0.02% by mass, it is instructed that it’s reclaimed; in any other case, an oil change is really helpful.
j) Interfacial pressure
This isn’t a routine check
PropertyCategoryGoodFairPoor
Interfacial Tension (mN/m)O, A, B, C, DInhibited Uninhibited>28 >2522 to 28 20 to 25<22 <20
ENot a routine check
F, GNot Applicable
The interfacial rigidity between transformer oil and water reduces in the course of the getting older course of. What this implies in practical terms is there could be more polar compound current within the oil, reducing 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 pressure becomes a high quality criterion: the oil have to be modified below a predefined limit.
If outcomes are GOOD, proceed the common sampling interval.
If results are FAIR, decrease the sampling interval.
If results are POOR, verify the oil for sediment and/or sludge.
k) Corrosive sulfur
This is not a routine test.
Oil is both corrosive or non-corrosive.
The presence of corrosive sulfur in transformer oil and its effect on the transformer system can be significant. The extent of the corrosion damage brought on by the sulfur could be so extreme that it might cause failure of the equipment if not checked. The addition of a copper passivator can reduce the impact of this compound on the transformer system.
In a examine by Doble, it has been discovered that rubber merchandise utilized in transformers may add to the corrosivity of the oil. Nitrile rubber gaskets and hoses not accredited 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 danger evaluation examine. [4]
l) Particle counting and sizing
Table three: Particles
Table B.1 – Typical contamination ranges (particles) encountered on energy transformer insulating oil as measured using IEC 60970 [5]
m) Flashpoint ° C
Not a routine check
If there’s a maximum lower in flashpoints by 10%, the gear may require additional inspection. This value would possibly differ in several international locations.
It is advised to perform this check when an unusual odour is noticed, the unit has been refilled, or an inner fault has occurred.
n) PCB (Polychlorinated Biphenyls)
This test is to not determine the situation of the transformer; it is a well being and safety influence test. PCB is hazardous to both humans and the setting; it is important to check for PCBs after the retro fill of a transformer. It is also required every time any maintenance has been done on the unit, and the potential for contamination is current. If PCB content exceeds the beneficial limits, the suitable action needs to be taken.
Units with a PCB content material of greater than 50ppm require a hearth safety plan, environmental protection plan, and extra precautionary measures when maintenance is done. This oil must be changed, and the oil disposed of as hazardous waste, with a certificate of secure disposal issued to the tools proprietor.
Local regulatory bodies define the limits.
o) DGA (Dissolved Gas Analysis)
As DGA is an intricate science with lots of knowledge and interpretation, we’ll talk about this phenomenon in part II of the article. The limits for the completely different gases and the interpretation of this data according to international standards will be mentioned in detail, forming part of the overall health rating willpower of the transformer.
Conclusion
Transformer situation monitoring is an interlaced, extremely thrilling subject of research. In this text, we targeted on the kinds of tests to determine the situation of the transformer, the important 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 potential to ensure greatest follow application and optimised upkeep. It additionally make it simpler to attract up a maintenance plan and action plan.
References:
1. IEC 60422 Edition 4.zero 2013-01 International Standard (Mineral insulating oils in electrical equipment – supervision and upkeep guide)
2. Oxidation inhibitor and reinhabiting oil-filled transformers, by Andy Shkolnik
3. Passivators, what they are and how 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 published by Transformer Technology Magazine Issue 16 – December 2021 https://www.transformer-technology.com
Author bio:
Corné Dames is a WearCheck transformer consultant. She has 20+ years’ experience in the trade, having previously worked as laboratory manager for a serious industrial laboratory group, focusing on transformer well being. She has been intrigued by transformer chemistry proper from the beginning of her profession, particularly in the analysis of test data. Corné has vast sensible and theoretical knowledge of reliability maintenance programmes.
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