Menu
PETROL CHEMICALS
TALKING TRANSFORMER TESTING
by Brenna ShumbamhiniJune 9, 2022
Share
Introduction
Corne Dames
Condition monitoring is the frequent amassing, measuring, recording, and evaluation of the related knowledge concerning an asset’s operation. If we interpret the data appropriately, it may give us great perception into the asset’s situation.
Frequent monitoring of the asset can outcome in much less maintenance required or more prolonged intervals without any maintenance required.
It is crucial to determine the key parameters which are needed to give us a complete picture of the actual standing 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 info telling us?
Has the condition of the unit modified since the last maintenance period?
Is it secure to function the unit?
Are there indicators of deterioration?
Is it protected to load the unit above the nameplate rating for a selected 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 recognized issues of a recurring nature?
Effective situation monitoring outline
It is vitally necessary to determine clear goals as part of your technique. What do you need to achieve by implementing this condition monitoring plan? Is it in-service failure prevention? Or maybe life extension? Maintenance deferral? By stipulating the outcome and what you need to accomplish, it will be a lot simpler to determine the required parameters.
Health indexing of assets is becoming a exceptional software in getting a clearer image of the situation of your transformer. Test parameters carry a numerical value-adding to the entire value of the Health Index Value of the transformer. These parameter weight values had been calculated primarily based on the international requirements for mineral oils, indicating the crucial values stipulated within the various standards.
The scope of oil evaluation, interpretation of the information, and important values
At the beginning of this part, it is essential to state that we deal with different dimension transformers in the business. Transformers are divided into courses based on the kV rankings of the gear. It is as a lot as the reliability or asset manager to make use of the guidelines for bigger equipment, thereby implementing shorter increment oil analysis and electrical exams.
The maintenance engineer or manager needs to find out what sort of testing would profit him in figuring out downside areas within his fleet. Some of the evaluation has been identified as to routine type exams. Still, there’s an intensive range of exams that may assist in figuring out specific drawback standards within the system, which could not be clear via the standard day-to-day evaluation usually carried out.
Please see the ranking courses in TABLE 1
TABLE 1 FIG
TABLE 2 explains which oil analyses are recommended and how typically or underneath which circumstances.
TABLE 2 FIG
Oil sampling
The taking of the oil sample is certainly one of the most vital and significant influencers in the analysis outcome. If a pattern is not taken to the prescribed process, then there’s a significant chance that the evaluation carried out, and the results acquired, are of no use.
Care should be taken to ensure quality control procedures are applied in every step of the sampling course of as set out by international standards. A good high quality sample taken by applying the proper procedure is essential. A pattern can be contaminated by numerous elements, all of which may influence the end result of the leads to a negative method.
All steps involved in pattern taking must adhere to high quality control procedures, including the container that’s used, the sampling kit, 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 pattern to the laboratory.
If the sample identification and sample data are handwritten, the human factor can lead to incorrect interpretation of the information. The label should be caught onto the container to make sure 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 put in writing on the label should be oil- and water resistant. Otherwise, some knowledge might be misplaced, making it extremely difficult for the laboratory personnel to finish the report or allocate the pattern to a particular transformer.
Now, let’s discuss the kinds of exams to determine the transformer’s condition, the crucial values, and the really helpful actions in each case:
a) Colour and look
This is a routine inspection utilized to every oil pattern.
When an oil sample arrives at the laboratory, one of the “tests” is a visible inspection of the oil sample in a transparent vessel to find out the color, turbidity, and potential particle identification.
Dark oils would possibly indicate chemical degradation or contamination of the oil.
When there’s a lot of turbidity, it’d point out a excessive water content within the oil.
If the drain valve was not cleaned by the sampler, the dirt particles in the drain valve may be incorporated into the sample. If particles are identified as carbon, it would indicate a possible electrical fault in the unit. The DGA evaluation of the oil will verify if so.
Clear oils with out contamination will indicate an excellent condition, and no motion is really helpful.
When oils are dark or turbid, additional analysis will confirm any problems. The oil evaluation results will also decide the degree and type of action.
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 point application<40 kV for OLTC in delta or line-end software
G <30
This is a routine inspection.
Breakdown voltage will point out the water content or the presence of foreign particles, or both in the oil being analysed.
As the oil in transformers acts as an insulation medium to avoid flashover in the unit, the breakdown voltage must be high.
If the values are Good, it is suggested to proceed with the current sample interval action plan.
If the values are Fair, more frequent sampling is really helpful in collaboration with other parameter results like the water content material, DDF (dielectric dissipation factor), and acidity.
If values are Poor – it is suggested to recondition the oil by way of oil reconditioning processes. If alternative checks point out extreme growing older, the oil can be changed 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 advantage 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 benefit is that the oil could be re-used, and in most conditions, this can be done with out switching off the unit, which contributes to cost-saving. If unsure – as an alternative swap off the unit during this therapy course of.
If the values are Poor, it’s advisable to take action as soon as potential and never delay the upkeep process. Excess water within the transformer system decreases the projected transformer lifetime significantly; extremely high water content could cause flashover within the unit, leading to loss of the asset.
c) Water content (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 check
This is a routine take a look at for all courses of electrical equipment, except class G
The outcomes of this test should at all times be thought of at the aspect of the breakdown power. If it’s found that the water content material is high and the breakdown energy is low, further action must be taken. It is beneficial that a second pattern from the same unit is tested to verify the results.
In the case of switching equipment, where there is not a paper current, the breakdown voltage is the determining factor.
It ought to be noted that the boundaries indicated by IEC 60422 Edition four apply to transformers with operating temperatures between 40 and 70 °C. If it is found that the unit’s operating temperature is exterior this temperature vary, it’s best to check with Annex A of the standard.
When the worth obtained via analyses is GOOD, the normal sampling interval could be maintained, requiring no additional action.
When the worth returns a FAIR result, more frequent sampling is recommended. It can also be helpful to consider different parameters like the breakdown voltage, particle content material and DDF/resistivity, and acidity to decide on the action to be implemented.
A POOR end result will require immediate motion from the asset supervisor. This would possibly include taking another sample to substantiate the outcomes from the primary analysis. If it is confirmed that the water content material is high, the oil can be filtered; this course of ought to remove a big portion of the moisture from the oil if applied accurately. Follow-up samples have to be taken to ensure that the moisture content material remains to be throughout the required limits. The cause is that essentially 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 situations that favour this motion. It may be found later that the oil within the water has elevated again without any obvious cause, however the supply can be the paper in the transformer.
A visual inspection can be recommended to discover out if any water would possibly move into the transformer or electrical equipment via leaks. This drawback may be more severe if the transformer or electrical gear is outside and never in a lined space.
d) Acidity (mgKOH/g oil) Neutralization Number
PropertyCategoryGoodFairPoor
Acidity mgKOH/g oilO, A, D<0.one 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 check
This is a routine take a look at for all classes except F and G
The acids in oils are formed 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’s going to adversely have an effect on the insulation properties of the oil and can enhance paper degradation. If left untreated in transformers, this will result in sludge formation, usually around the decrease parts of the transformer core. The sludge will finally kind a semi-solid substance that’s extraordinarily tough to take away.
If the result’s GOOD, the regular sampling interval can continue.
In case of a FAIR outcome, the sampling interval ought to be decreased to fit the state of affairs. Future analysis ought to embody a visible inspection of the oil for sediment and sludge.
If the result is POOR based on the prescribed values in IEC 60422 Edition four.zero, the asset manager could determine to reclaim the oil or exchange it with new or reclaimed oil, whichever choice would possibly swimsuit their requirements the most effective.
e) Dielectric Dissipation issue at 40Hz to 60Hz at 90° C
PropertyCategoryGoodFairPoor
Dielectric Dissipation factorAt 40Hz to 60Hz at 90°CO, A<0.a hundred.10 to 0.20>0.20
B, C<0.one hundred.10 to 0.50>0.50
D<0.010.01 to 0.03>0.03
E<0.one hundred.01 to zero.30>0.03
F, GNot a routine check
This is a routine test for all courses of electrical equipment, besides F and G
The dielectric dissipation issue or tan delta of this test provides information regarding the extent of the dielectric losses in transformer oil. This take a look at measures the inefficiency of insulating material.
When oil ages, we now have the formation of polar compounds, resulting in phase displacement and dielectric losses. Other impurities that might affect the dissipation issue include water, dissolved insulating resin, and paper.
When the result is FAIR, extra frequent sampling and checking additional parameters is really helpful.
When the result’s POOR, reclamation or an oil change is beneficial. The structure of the oil is damaged, in impact that the chemical bonds between the molecules have damaged down, and even with filtration, the beneficial 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 certainly one of the key parameters to assess the transformer insulation situation; that is primarily based on the reality that DC resistance is sensitive to grease degradation.
When the result’s FAIR, extra frequent sampling and checking extra parameters is recommended.
When the result’s POOR, reclamation or an oil change is recommended.
g) Inhibitor content material percent
PropertyCategoryGoodFairPoor
Inhibitor Content %AllRestricted to Inhibited oils,Consult oil supplier40% to 60% Of unique value<40% of original value
This check is restricted to oils with this additive.
It would be advisable to contact the oil supplier to verify the details regarding components.
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 purpose of the inhibitor is to stop oxygen from reacting with the oil. This significantly slows the aging process in the oil and the strong insulation.
If the result’s FAIR, it is advised to top up the inhibitor stage to the prescribed stage per provider directions. It is suggested to use a field skilled educated in the process to perform this task.
If the result obtained is POOR, the advice for this situation would counsel that the end person continues to use the oil “uninhibited,” but this may result in more speedy degradation of each the liquid and strong insulation.
It should be famous that some transformers have already got a built-in oil preservation system; this is designed to keep dissolved oxygen at ranges beneath 1000ppm. This would be within the type of a nitrogen system, a nitrogen tank or generator, or a conservator tank geared up with a rubber diaphragm (bladder). Using inhibited oils beneath these circumstances isn’t required, though it’d add extra protection in opposition to 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 stable, (rate of lower < 10/mg/kg/year)50-70mg/kg or<70mg/kg, with a significantrate of decrease of >10mg/kg/year<50 and decreasing at >10mg/kg/year
Passivators, also recognized as steel deactivators, react with reactive steel surfaces and dissolved metals similar to copper and silver and reduce their fee 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 fundamental sorts, sulfur-based and nitrogen-based. The first suggested 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 extra rapidly; this depletion might accelerate when the oil is un-inhibited.
With GOOD results, regular pattern intervals could be maintained.
With FAIR outcomes, preserve regular monitoring.
When POOR, it’s suggested to take away the oil or remove the supply of corrosivity from the oil by way of special oil remedy.
I) Sediment and sludge
This just isn’t a routine take a look at.
It is advised that this take a look at is performed when the oil outcomes point out a excessive acid value and the dissipation issue is close to the unacceptable restrict.
The results must be lower than 0.02% by mass to be negligible. If the outcomes return a price of greater than zero.02% by mass, it’s advised that it be reclaimed; otherwise, an oil change is recommended.
j) Interfacial tension
This just isn’t a routine test
PropertyCategoryGoodFairPoor
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 tension between transformer oil and water reduces during the getting older process. What pressure gauge 2.5 นิ้ว implies in sensible terms is there is extra polar compound present within the oil, decreasing the flexibility of an oil to serve as an insulator within the transformer system. There is a direct correlation between interfacial pressure and neutralisation quantity. Therefore, the interfacial tension turns into a excessive quality criterion: the oil should be modified below a predefined limit.
If outcomes are GOOD, proceed the common sampling interval.
If outcomes are FAIR, decrease the sampling interval.
If outcomes are POOR, examine 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 vital. The extent of the corrosion damage caused by the sulfur could be so severe that it’d trigger failure of the tools if not checked. The addition of a copper passivator can scale back the impression of this compound on the transformer system.
In a study by Doble, it has been found that rubber products used in transformers might add to the corrosivity of the oil. Nitrile rubber gaskets and hoses not approved for oil filtration may contaminate the oil with corrosive sulfur.
CIGRE Brochure no 378, 2009 stipulates the need of corrective actions based on this institute’s danger evaluation study. [4]
l) Particle counting and sizing
Table 3: 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 test
If there is a maximum lower in flashpoints by 10%, the tools would possibly require further inspection. This value may differ in several countries.
It is suggested to perform this take a look at when an unusual odour is seen, the unit has been refilled, or an inside fault has occurred.
n) PCB (Polychlorinated Biphenyls)
This take a look at is not to decide the situation of the transformer; this is a health and security impact take a look at. PCB is hazardous to both people and the setting; it is important to test for PCBs after the retro fill of a transformer. It can be required whenever any upkeep has been carried out on the unit, and the potential for contamination is present. If PCB content material exceeds the really helpful limits, the suitable action needs to be taken.
Units with a PCB content material of more than 50ppm require a hearth security plan, environmental safety plan, and further precautionary measures when maintenance is done. This oil needs to be changed, and the oil disposed of as hazardous waste, with a certificate of secure disposal issued to the tools proprietor.
Local regulatory our bodies define the boundaries.
o) DGA (Dissolved Gas Analysis)
As DGA is an intricate science with a lot of data and interpretation, we are going to discuss this phenomenon partially II of the article. The limits for the totally different gases and the interpretation of this data based on international standards shall be mentioned intimately, forming a part of the overall health score dedication of the transformer.
Conclusion
Transformer situation monitoring is an interlaced, extremely thrilling field of research. In this article, we targeted on the types of checks to find out the condition of the transformer, the crucial values, and the beneficial actions.
The Health Index indication makes it potential to see the supposed reliability of a specific unit at a selected date and time. This makes it attainable to make sure greatest follow application and optimised maintenance. It additionally make it simpler to attract up a upkeep plan and motion plan.
References:
1. IEC 60422 Edition four.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
three. Passivators, what they’re and the way 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 energy.”
6. Article initially revealed by Transformer Technology Magazine Issue 16 – December 2021 https://www.transformer-technology.com
Author bio:
Corné Dames is a WearCheck transformer marketing consultant. She has 20+ years’ expertise within the industry, having previously worked as laboratory manager for a serious industrial laboratory group, focusing on transformer health. She has been intrigued by transformer chemistry right from the beginning of her career, notably in the evaluation of check knowledge. Corné has huge sensible and theoretical information of reliability upkeep programmes.
Share
รับตัวแทนจำหน่าย และขายส่งฟิตติ้งสแตนเลส , มีสินค้าพร้อมส่ง , ไม่ต้องสต๊อกสินค้า , จัดส่งฟรีกรุงเทพ ปริมณฑล , ต่างจังหวัดจัดส่งขนส่ง ฟรีทั่วประเทศไทย
octa-gauge.com & radiusglobal.co.th Shop power by Odoo ERP
