PETROL CHEMICALS
TALKING TRANSFORMER TESTING
by Brenna ShumbamhiniJune 9, 2022
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Introduction
Corne Dames
Condition monitoring is the frequent accumulating, measuring, recording, and analysis of the relevant data relating to an asset’s operation. If we interpret the data appropriately, it can provide us nice insight into the asset’s situation.
Frequent monitoring of the asset can end result in less upkeep required or extra extended periods with none maintenance required.
It is crucial to establish the important thing parameters that 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 realize the utmost lifetime.
What is the info telling us?
Has the situation of the unit modified for the reason that final maintenance period?
Is it protected to function the unit?
Are there signs of deterioration?
Is it secure 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 lengthy can we use the unit before we need to contemplate replacement?
Are the recognized problems of a recurring nature?
Effective situation monitoring define
It is vitally important to establish clear objectives as a half of your technique. What do you want to achieve by implementing this condition monitoring plan? Is it in-service failure prevention? Or maybe life extension? Maintenance deferral? By stipulating the result and what you wish to accomplish, it would be much easier to determine the required parameters.
Health indexing of belongings is changing into a exceptional tool in getting a clearer picture of the condition of your transformer. Test parameters carry a numerical value-adding to the whole worth of the Health Index Value of the transformer. These parameter weight values were calculated based on the worldwide requirements for mineral oils, indicating the critical values stipulated within the various standards.
The scope of oil analysis, interpretation of the info, and important values
At the start of this section, it’s essential to state that we take care of different measurement transformers in the business. Transformers are divided into lessons in accordance with the kV ratings of the equipment. It is as much as the reliability or asset supervisor to make use of the guidelines for bigger equipment, thereby implementing shorter increment oil analysis and electrical tests.
The maintenance engineer or supervisor wants to discover out what kind of testing would profit him in figuring out problem areas within his fleet. Some of the evaluation has been recognized as to routine type tests. Still, there’s an extensive vary of tests that can assist in figuring out particular drawback criteria within the system, which could not be clear via the everyday day-to-day evaluation often performed.
Please see the score classes in TABLE 1
TABLE 1 FIG
TABLE 2 explains which oil analyses are beneficial and the way often or beneath which circumstances.
TABLE 2 FIG
Oil sampling
The taking of the oil sample is doubtless one of the most vital and important influencers in the evaluation outcome. If a sample is not taken to the prescribed procedure, then there is a important possibility that the evaluation performed, and the results 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 worldwide requirements. A good high quality pattern taken by making use of the proper procedure is crucial. A sample could be contaminated by various components, all of which might influence the end result of the ends in a unfavorable manner.
All steps concerned in pattern taking should adhere to high quality management procedures, including the container that is used, the sampling package, the taking of the pattern, the marking of the pattern, the closing of the sample, the storage and handling of the pattern, and then the delivery of the pattern to the laboratory.
If the sample identification and pattern data are handwritten, the human factor can result in incorrect interpretation of the information. 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 should be waterproof, and the pen used to write on the label ought to be oil- and water resistant. Otherwise, some data might be lost, making it extraordinarily difficult for the laboratory personnel to finish the report or allocate the sample to a particular transformer.
Now, let’s focus on the forms of exams to determine the transformer’s condition, the critical values, and the really helpful actions in every case:
a) Colour and look
This is a routine inspection applied to every oil pattern.
When an oil sample arrives on the laboratory, one of many “tests” is a visible inspection of the oil sample in a clear vessel to find out the colour, turbidity, and attainable particle identification.
Dark oils may point out chemical degradation or contamination of the oil.
When there may be plenty of turbidity, it might point out a high water content within the oil.
If the drain valve was not cleaned by the sampler, the dust particles within the drain valve could be included into the pattern. If particles are identified as carbon, it’d point out a potential electrical fault in the unit. The DGA analysis of the oil will verify if so.
Clear oils without contamination will indicate an excellent condition, and no motion is really helpful.
When oils are darkish or turbid, additional evaluation will verify any problems. The oil evaluation outcomes may also determine the diploma and type 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 point application<40 kV for OLTC in delta or line-end application
G <30
This is a routine inspection.
Breakdown voltage will indicate the water content or the presence of overseas particles, or each within 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 strongly recommended to proceed with the current pattern interval action 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 strongly recommended to recondition the oil via oil reconditioning processes. If alternative exams indicate extreme growing older, the oil may be replaced with new or reclaimed oil. Another choice could be to carry out on-site oil reclamation utilizing a reclamation plant.
Reclamation of oil has the advantage that the colour of the oil is restored, and the polar components 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 might be accomplished with out switching off the unit, which contributes to cost-saving. If doubtful – as a substitute switch off the unit during this treatment process.
If the values are Poor, it is advisable to take motion as soon as attainable and never delay the maintenance process. Excess water in the transformer system decreases the projected transformer lifetime considerably; extremely high water content may 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 test
This is a routine test for all lessons of electrical tools, besides class G
The results of this check should always be thought of along side the breakdown strength. If it is found that the water content is excessive and the breakdown power is low, further motion needs to be taken. It is really helpful that a second sample from the same unit is tested to verify the results.
In the case of switching tools, where there isn’t any paper current, the breakdown voltage is the figuring out issue.
It must be famous that the bounds indicated by IEC 60422 Edition four apply to transformers with working temperatures between 40 and 70 °C. If it is discovered that the unit’s operating temperature is outside this temperature vary, it’s best to discuss with Annex A of the standard.
When the value obtained by way of analyses is GOOD, the traditional sampling interval could be maintained, requiring no additional motion.
When the worth returns a FAIR outcome, extra frequent sampling is beneficial. It is also useful to assume about other parameters like the breakdown voltage, particle content material and DDF/resistivity, and acidity to decide on the motion to be implemented.
A POOR outcome would require instant action from the asset manager. This would possibly embody taking one other pattern to substantiate the outcomes from the first analysis. If it is confirmed that the water content is excessive, the oil could be filtered; this course of should remove a large portion of the moisture from the oil if applied accurately. Follow-up เกจวัดแรงดันดิจิตอล have to be taken to ensure that the moisture content material is still throughout the required limits. The cause is that the most significant slice of the water is caught up in the paper system in the transformer. This moisture will transfer from the paper into the oil underneath conditions that favour this motion. It might be found later that the oil within the water has increased once more without any apparent purpose, but the source could be the paper within the transformer.
A visual inspection can be beneficial to determine if any water may transfer into the transformer or electrical tools by way of leaks. This downside could be more extreme if the transformer or electrical equipment is exterior and never in a coated area.
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.one hundred.10 to 0.25>0.20
C<0.one hundred.15 to zero.30>0.30
F, G Not a routine check
This is a routine check for all lessons besides F and G
The acids in oils are fashioned as a outcome of 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 will adversely affect the insulation properties of the oil and can increase paper degradation. If left untreated in transformers, this could lead to sludge formation, normally around the lower elements of the transformer core. The sludge will eventually kind a semi-solid substance that is extraordinarily troublesome to remove.
If the result is GOOD, the regular sampling interval can continue.
In case of a FAIR end result, the sampling interval should be decreased to fit the scenario. Future evaluation ought to include a visual inspection of the oil for sediment and sludge.
If the result’s POOR according to the prescribed values in IEC 60422 Edition 4.0, the asset manager could decide to reclaim the oil or exchange it with new or reclaimed oil, whichever possibility might suit their requirements 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.a hundred.10 to 0.50>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, except F and G
The dielectric dissipation factor or tan delta of this test provides data concerning the extent of the dielectric losses in transformer oil. This check measures the inefficiency of insulating material.
When oil ages, we have the formation of polar compounds, resulting in phase displacement and dielectric losses. Other impurities that might affect the dissipation issue embrace water, dissolved insulating resin, and paper.
When the result is FAIR, extra frequent sampling and checking further parameters is beneficial.
When the result is POOR, reclamation or an oil change is really helpful. The structure of the oil is broken, in effect that the chemical bonds between the molecules have damaged down, and even with filtration, the recommended 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 take a look at
DC resistivity of the oil is among the key parameters to assess the transformer insulation condition; that is primarily based on the reality that DC resistance is sensitive to oil degradation.
When the result’s FAIR, more frequent sampling and checking additional parameters is really helpful.
When the result’s POOR, reclamation or an oil change is beneficial.
g) Inhibitor content material %
PropertyCategoryGoodFairPoor
Inhibitor Content %AllRestricted to Inhibited oils,Consult oil supplier40% to 60% Of authentic value<40% of unique worth
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 components.
The two most typical 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 prevent oxygen from reacting with the oil. This considerably slows the aging course of in the oil and the stable insulation.
If the result’s FAIR, it’s suggested to high up the inhibitor degree to the prescribed level per provider directions. It is advised to make use of a field skilled trained in the procedure to perform this activity.
If the result obtained is POOR, the advice for this state of affairs would recommend that the tip user continues to make use of the oil “uninhibited,” however this will result in extra rapid degradation of each the liquid and strong insulation.
It must be famous that some transformers already have a built-in oil preservation system; this is designed to keep dissolved oxygen at levels beneath 1000ppm. This would be within the type 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, though it would add extra 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 steady, (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 called steel deactivators, react with reactive steel surfaces and dissolved metals corresponding to copper and silver and cut back their price of response 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 suggested use of passivators in transformer oil, of which the writer 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 more quickly; this depletion would possibly accelerate when the oil is un-inhibited.
With GOOD results, regular pattern intervals can be maintained.
With FAIR outcomes, preserve regular monitoring.
When POOR, it’s advised to remove the oil or remove the source of corrosivity from the oil via special oil therapy.
I) Sediment and sludge
This isn’t a routine test.
It is suggested that this check is performed when the oil outcomes point out a high acid value and the dissipation issue is near the unacceptable limit.
The results must be less than zero.02% by mass to be negligible. If the results return a value of more than 0.02% by mass, it’s advised that or not it’s reclaimed; otherwise, an oil change is really helpful.
j) Interfacial pressure
This isn’t a routine test
PropertyCategoryGoodFairPoor
Interfacial Tension (mN/m)O, A, B, C, DInhibited Uninhibited>28 >2522 to 28 20 to 25<22 <20
ENot a routine take a look at
F, GNot Applicable
The interfacial pressure between transformer oil and water reduces in the course of the growing older process. What this means in practical phrases is there is extra polar compound current in the oil, reducing the flexibility of an oil to serve as an insulator in the transformer system. There is a direct correlation between interfacial tension and neutralisation quantity. Therefore, the interfacial pressure turns into a high quality criterion: the oil have to be modified below a predefined restrict.
If outcomes are GOOD, continue the regular sampling interval.
If results are FAIR, decrease the sampling interval.
If outcomes are POOR, check the oil for sediment and/or sludge.
k) Corrosive sulfur
This just 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 can be significant. The extent of the corrosion harm brought on by the sulfur could be so severe that it would cause failure of the equipment if not checked. The addition of a copper passivator can scale back the influence of this compound on the transformer system.
In a examine by Doble, it has been discovered that rubber products used in transformers would possibly add to the corrosivity of the oil. Nitrile rubber gaskets and hoses not approved for oil filtration would possibly contaminate the oil with corrosive sulfur.
CIGRE Brochure no 378, 2009 stipulates the need of corrective actions based mostly on this institute’s risk evaluation research. [4]
l) Particle counting and sizing
Table three: Particles
Table B.1 – Typical contamination levels (particles) encountered on power transformer insulating oil as measured utilizing IEC 60970 [5]
m) Flashpoint ° C
Not a routine check
If there’s a most decrease in flashpoints by 10%, the tools would possibly require additional inspection. This value would possibly differ in several countries.
It is suggested to perform this test when an unusual odour is observed, the unit has been refilled, or an internal fault has occurred.
n) PCB (Polychlorinated Biphenyls)
This check is not to determine the condition of the transformer; it is a well being and security impression check. PCB is hazardous to each humans and the setting; it’s critical to test for PCBs after the retro fill of a transformer. It can be required each time any maintenance has been accomplished on the unit, and the potential for contamination is current. If PCB content material exceeds the beneficial limits, the appropriate motion needs to be taken.
Units with a PCB content material of greater than 50ppm require a hearth safety plan, environmental safety plan, and additional precautionary measures when upkeep is completed. This oil needs to be replaced, and the oil disposed of as hazardous waste, with a certificates of safe disposal issued to the equipment owner.
Local regulatory bodies define the limits.
o) DGA (Dissolved Gas Analysis)
As DGA is an intricate science with a lot of data and interpretation, we will focus on this phenomenon partly II of the article. The limits for the different gases and the interpretation of this information according to international requirements shall be discussed intimately, forming part of the general health rating dedication of the transformer.
Conclusion
Transformer situation monitoring is an interlaced, extremely thrilling subject of research. In this text, we focused on the forms of exams to find out the situation of the transformer, the critical values, and the beneficial actions.
The Health Index indication makes it potential to see the supposed reliability of a specific unit at a specific date and time. This makes it potential to make sure greatest follow software and optimised maintenance. It also make it simpler to attract up a upkeep plan and action plan.
References:
1. IEC 60422 Edition four.0 2013-01 International Standard (Mineral insulating oils in electrical gear – supervision and upkeep guide)
2. Oxidation inhibitor and reinhabiting oil-filled transformers, by Andy Shkolnik
3. 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 sixteen – December 2021 https://www.transformer-technology.com
Author bio:
Corné Dames is a WearCheck transformer marketing consultant. She has 20+ years’ expertise in the industry, having previously labored as laboratory manager for a serious industrial laboratory group, specializing in transformer well being. She has been intrigued by transformer chemistry proper from the beginning of her profession, notably within the evaluation of take a look at data. Corné has vast practical and theoretical data of reliability upkeep programmes.
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