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PETROL CHEMICALS
TALKING TRANSFORMER TESTING
by Brenna ShumbamhiniJune 9, 2022
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Introduction
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 info appropriately, it can give us great perception into the asset’s situation.
Frequent monitoring of the asset can end result in less maintenance required or more extended durations without any maintenance required.
It is crucial to identify the key parameters which are needed to provide us a whole picture of the actual standing of the transformer and the action we have to take to make sure the continued reliability of the asset to achieve the utmost lifetime.
What is the information telling us?
Has the situation of the unit changed for the rationale that final upkeep period?
Is it safe to operate the unit?
Are there indicators of deterioration?
Is it protected to load the unit above the nameplate ranking for a selected period?
Are we required to implement motion to make sure the continued reliability of the unit?
How long can we use the unit earlier than we need to consider replacement?
Are the recognized problems of a recurring nature?
Effective condition monitoring outline
It is vitally necessary to identify clear goals as a half of your strategy. What do you wish to achieve by implementing this condition monitoring plan? Is it in-service failure prevention? Or possibly life extension? Maintenance deferral? By stipulating the end result and what you want to accomplish, it will be a lot easier to identify the required parameters.
Health indexing of property is becoming a remarkable tool in getting a clearer picture of the condition of your transformer. Test parameters carry a numerical value-adding to the total worth of the Health Index Value of the transformer. These parameter weight values have been calculated primarily based on the worldwide requirements for mineral oils, indicating the crucial values stipulated in the various standards.
The scope of oil evaluation, interpretation of the information, and critical values
At the beginning of this section, it is important to state that we take care of totally different measurement transformers within the business. Transformers are divided into classes based on the kV ratings of the gear. It is up to the reliability or asset manager to use the guidelines for bigger tools, thereby implementing shorter increment oil analysis and electrical exams.
The maintenance engineer or manager needs to determine what sort of testing would benefit him in figuring out downside areas inside his fleet. Some of the evaluation has been identified as to routine kind tests. Still, there could be an extensive range of exams that may help in identifying specific problem standards within the system, which might not be clear through the standard day-to-day evaluation normally performed.
Please see the score classes in TABLE 1
TABLE 1 FIG
TABLE 2 explains which oil analyses are really helpful and how usually or underneath which circumstances.
TABLE 2 FIG
Oil sampling
The taking of the oil sample is doubtless considered one of the most crucial and important influencers in the evaluation consequence. If a pattern isn’t taken to the prescribed procedure, then there is a significant possibility that the evaluation performed, and the outcomes acquired, are of no use.
Care ought to be taken to ensure quality management procedures are applied in every step of the sampling process as set out by worldwide requirements. A good quality sample taken by making use of the right process is important. A pattern can be contaminated by varied factors, all of which might affect the result of the leads to a negative manner.
All steps involved in sample taking must adhere to high quality control procedures, including the container that is used, the sampling equipment, the taking of the pattern, the marking of the sample, the closing of the sample, the storage and dealing with of the pattern, after which the supply of the pattern to the laboratory.
If the pattern identification and sample knowledge 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 completed in neat, easy-to-read handwriting. The label should be waterproof, and the pen used to put in writing on the label must be oil- and waterproof. Otherwise, some data could be misplaced, making it extraordinarily tough for the laboratory personnel to finish the report or allocate the sample to a specific transformer.
Now, let’s focus on the kinds of tests to discover out the transformer’s condition, the critical values, and the really helpful actions in every case:
a) Colour and appearance
This is a routine inspection applied 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 clear vessel to discover out the color, turbidity, and potential particle identification.
Dark oils may indicate chemical degradation or contamination of the oil.
When there is lots of turbidity, it’d point out a excessive water content material in the oil.
If the drain valve was not cleaned by the sampler, the dirt particles in the drain valve might be included into the pattern. If particles are recognized as carbon, it might point out a possible electrical fault within the unit. The DGA analysis of the oil will affirm if this is the case.
Clear oils with out contamination will point out a great situation, and no action is really helpful.
When oils are darkish or turbid, further analysis will affirm any problems. The oil analysis outcomes will also decide 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 foreign particles, or both in the oil being analysed.
As the oil 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 suggested to continue with the present sample interval action plan.
If the values are Fair, more frequent sampling is really helpful in collaboration with different parameter results just like the water content, DDF (dielectric dissipation factor), and acidity.
If values are Poor – it is strongly recommended to recondition the oil via oil reconditioning processes. If various tests indicate extreme growing older, the oil could be changed with new or reclaimed oil. Another possibility could be to perform on-site oil reclamation utilizing a reclamation plant.
Reclamation of oil has the benefit 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 can be re-used, and in most conditions, this can be carried out with out switching off the unit, which contributes to cost-saving. If doubtful – instead change off the unit throughout this remedy course of.
If the values are Poor, it’s advisable to take action as quickly as attainable and not delay the upkeep process. Excess water in the transformer system decreases the projected transformer lifetime considerably; extraordinarily high water content material could cause flashover within the unit, leading to loss of the asset.
c) Water content (mg/kg at transformer working 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 take a look at
This is a routine check for all classes of electrical gear, besides class G
The outcomes of this check ought to at all times be considered along side the breakdown energy. If it is found that the water content is excessive and the breakdown energy is low, further action needs to be taken. It is beneficial that a second sample from the same unit is examined to substantiate the results.
In the case of switching gear, the place there is not a paper present, the breakdown voltage is the determining factor.
It must be famous that the limits indicated by IEC 60422 Edition four apply to transformers with working temperatures between 40 and 70 °C. If it’s found that the unit’s operating temperature is exterior this temperature vary, it is best to check with Annex A of the usual.
When the worth obtained via analyses is GOOD, the conventional sampling interval could be maintained, requiring no additional motion.
When the worth returns a FAIR result, extra frequent sampling is recommended. It is also useful to suppose about different parameters just like the breakdown voltage, particle content and DDF/resistivity, and acidity to resolve on the action to be implemented.
A POOR outcome would require instant action from the asset supervisor. This might embody taking another pattern to confirm the outcomes from the first evaluation. If it is confirmed that the water content is high, the oil may be filtered; this course of should remove a big portion of the moisture from the oil if utilized accurately. Follow-up samples need to be taken to make sure that the moisture content material remains to be throughout the required limits. The reason is that the most good portion of the water is caught up within the paper system within the transformer. This moisture will transfer from the paper into the oil beneath circumstances that favour this motion. It may be discovered later that the oil in the water has increased again with none obvious purpose, but the supply could be the paper within the transformer.
A visible inspection can also be beneficial to determine if any water would possibly move into the transformer or electrical tools through leaks. This problem could be more extreme if the transformer or electrical tools is outside and never in a coated space.
d) Acidity (mgKOH/g oil) Neutralization Number
PropertyCategoryGoodFairPoor
Acidity mgKOH/g oilO, A, D<0.a hundred.10 to zero.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 check
This is a routine test for all lessons except F and G
The acids in oils are fashioned due to chemical reactions between the oil, water, and paper. Higher temperatures or load increases will assist within the formation of the acids. Because acids are polar compounds, it’ll adversely have an result on the insulation properties of the oil and can enhance paper degradation. If left untreated in transformers, this could result in sludge formation, often across the decrease components of the transformer core. The sludge will ultimately type a semi-solid substance that is extraordinarily tough to remove.
If the result is GOOD, the regular sampling interval can proceed.
In case of a FAIR end result, the sampling interval should be decreased to suit the state of affairs. Future analysis ought to embody a visual inspection of the oil for sediment and sludge.
If the result is POOR according to the prescribed values in IEC 60422 Edition four.zero, the asset supervisor could decide to reclaim the oil or replace it with new or reclaimed oil, whichever choice might suit their requirements one of the best.
e) Dielectric Dissipation factor at 40Hz to 60Hz at 90° C
PropertyCategoryGoodFairPoor
Dielectric Dissipation factorAt 40Hz to 60Hz at 90°CO, A<0.100.10 to 0.20>0.20
B, C<0.100.10 to 0.50>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 test
This is a routine test for all classes of electrical tools, besides F and G
The dielectric dissipation factor or tan delta of this test provides info concerning the extent of the dielectric losses in transformer oil. This take a look at measures the inefficiency of insulating materials.
When oil ages, we have the formation of polar compounds, resulting in part displacement and dielectric losses. Other impurities that might influence the dissipation issue embody water, dissolved insulating resin, and paper.
When the result’s FAIR, more frequent sampling and checking extra parameters is really helpful.
When the result is POOR, reclamation or an oil change is recommended. The construction of the oil is broken, in impact that the chemical bonds between the molecules have broken 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 check
DC resistivity of the oil is likely one of the key parameters to assess the transformer insulation condition; that is primarily based on the fact that DC resistance is delicate to grease degradation.
When the result’s FAIR, extra frequent sampling and checking extra parameters is really helpful.
When the result is POOR, reclamation or an oil change is beneficial.
g) Inhibitor content %
PropertyCategoryGoodFairPoor
Inhibitor Content %AllRestricted to Inhibited oils,Consult oil supplier40% to 60% Of authentic value<40% of unique worth
This take a look at is restricted to oils with this additive.
It can be advisable to contact the oil provider to confirm the main 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 objective of the inhibitor is to stop oxygen from reacting with the oil. This significantly slows the aging process within the oil and the strong insulation.
If the result’s FAIR, it’s suggested to top up the inhibitor stage to the prescribed degree per supplier directions. It is advised to make use of a subject professional educated in the process to carry out this activity.
If the end result obtained is POOR, the recommendation for this state of affairs would suggest that the end user continues to make use of the oil “uninhibited,” but this will lead to more speedy degradation of both the liquid and solid insulation.
ร้านซ่อมเครื่องวัดความดันโลหิต ought to be famous that some transformers already have a built-in oil preservation system; that is designed to keep dissolved oxygen at ranges below 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 underneath these circumstances just isn’t required, although it’d add additional safety in opposition to oil oxidation if the preservation system ever fails. [2]
h) Passivator content
PropertyCategoryGoodFairPoor
Passivator Content (mg/kg)O,A,B,C,D,E,F.>70 and stable, (rate of decrease < 10/mg/kg/year)50-70mg/kg or<70mg/kg, with a significantrate of decrease of >10mg/kg/year<50 and lowering at >10mg/kg/year
Passivators, also called steel deactivators, react with reactive metal surfaces and dissolved metals corresponding to copper and silver and reduce their price of reaction with compounds in the oil. This includes oxidation reactions with natural compounds and reactions with corrosive sulfur. Passivators are composed of two fundamental 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 would possibly deplete more rapidly; this depletion might accelerate when the oil is un-inhibited.
With GOOD results, common sample intervals could be maintained.
With FAIR outcomes, preserve regular monitoring.
When POOR, it is suggested to take away the oil or remove the source of corrosivity from the oil through particular oil remedy.
I) Sediment and sludge
This is not a routine take a look at.
It is suggested that this take a look at is carried out when the oil outcomes indicate a excessive acid value and the dissipation issue is near the unacceptable limit.
The results must be less than 0.02% by mass to be negligible. If the results return a price of greater than zero.02% by mass, it’s instructed that or not it’s reclaimed; in any other case, an oil change is really helpful.
j) Interfacial pressure
This just isn’t a routine take a look at
PropertyCategoryGoodFairPoor
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 through the getting older course of. What this implies in sensible terms is there’s extra polar compound present within the oil, decreasing the power of an oil to function an insulator within the transformer system. There is a direct correlation between interfacial pressure and neutralisation quantity. Therefore, the interfacial rigidity turns into a high quality criterion: the oil must be changed under a predefined limit.
If results are GOOD, proceed the common sampling interval.
If outcomes are FAIR, lower the sampling interval.
If outcomes are POOR, examine 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 significant. The extent of the corrosion injury brought on by the sulfur could be so extreme that it might cause failure of the gear 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 found that rubber merchandise used in transformers may add to the corrosivity of the oil. Nitrile rubber gaskets and hoses not permitted for oil filtration might contaminate the oil with corrosive sulfur.
CIGRE Brochure no 378, 2009 stipulates the necessity of corrective actions based on this institute’s danger assessment examine. [4]
l) Particle counting and sizing
Table 3: Particles
Table B.1 – Typical contamination levels (particles) encountered on energy transformer insulating oil as measured utilizing IEC 60970 [5]
m) Flashpoint ° C
Not a routine check
If there is a most lower in flashpoints by 10%, the tools may require further inspection. This worth might differ in numerous countries.
It is advised to perform this take a look at when an uncommon odour is noticed, the unit has been refilled, or an inside fault has occurred.
n) PCB (Polychlorinated Biphenyls)
This take a look at is to not decide the condition of the transformer; it is a well being and safety influence test. PCB is hazardous to each people and the setting; it is important to test for PCBs after the retro fill of a transformer. It can also be required every time any upkeep has been accomplished on the unit, and the potential of contamination is current. If PCB content material exceeds the recommended limits, the suitable motion must be taken.
Units with a PCB content material of greater than 50ppm require a fire safety plan, environmental protection plan, and extra precautionary measures when upkeep is completed. This oil needs to be replaced, and the oil disposed of as hazardous waste, with a certificates of protected disposal issued to the tools owner.
Local regulatory our bodies outline the bounds.
o) DGA (Dissolved Gas Analysis)
As DGA is an intricate science with a lot of information and interpretation, we will talk about this phenomenon partly II of the article. The limits for the different gases and the interpretation of this data according to worldwide standards might be mentioned intimately, forming part of the general health rating willpower of the transformer.
Conclusion
Transformer condition monitoring is an interlaced, extremely thrilling subject of research. In this article, we centered on the forms of exams to find out the condition of the transformer, the critical values, and the recommended actions.
The Health Index indication makes it attainable to see the supposed reliability of a specific unit at a selected date and time. This makes it attainable to ensure greatest apply application and optimised maintenance. It additionally make it simpler to draw up a upkeep plan and motion plan.
References:
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 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 strength.”
6. Article initially revealed by Transformer Technology Magazine Issue sixteen – December 2021 https://www.transformer-technology.com
Author bio:
Corné Dames is a WearCheck transformer marketing consultant. She has 20+ years’ expertise within the business, having beforehand labored as laboratory manager for a significant industrial laboratory group, focusing on transformer health. She has been intrigued by transformer chemistry proper from the beginning of her career, notably in the analysis of test information. Corné has huge practical and theoretical information of reliability maintenance programmes.
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