TALKING TRANSFORMER TESTING

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 analysis of the related knowledge regarding an asset’s operation. If we interpret the info accurately, it may give us nice insight into the asset’s situation.
Frequent monitoring of the asset can lead to much less maintenance required or more prolonged periods with none upkeep required.
It is crucial to establish the important thing parameters which may be wanted to provide us a whole image of the actual status of the transformer and the action we have to take to ensure the continued reliability of the asset to realize the maximum lifetime.
What is the data telling us?
Has the condition of the unit changed for the reason that final upkeep period?
Is it protected to function the unit?
Are there indicators of deterioration?
Is it safe to load the unit above the nameplate ranking for a selected period?
Are we required to implement action to ensure the continued reliability of the unit?
How lengthy can we use the unit before we need to contemplate replacement?
Are the identified issues of a recurring nature?
Effective situation monitoring outline
It is vitally important to determine clear goals as part of your technique. What do you want to achieve by implementing this situation monitoring plan? Is it in-service failure prevention? Or maybe life extension? Maintenance deferral? By stipulating the end result and what you need to accomplish, it would be much simpler to determine the required parameters.
Health indexing of assets is turning into a exceptional software in getting a clearer picture 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 based mostly on the worldwide requirements for mineral oils, indicating the critical values stipulated in the numerous requirements.
The scope of oil analysis, interpretation of the information, and significant values
At the start of this part, it’s essential to state that we cope with totally different size transformers in the business. Transformers are divided into classes based on the kV rankings of the tools. It is up to the reliability or asset manager to use the rules for larger equipment, thereby implementing shorter increment oil evaluation and electrical tests.
The maintenance engineer or manager needs to determine what sort of testing would benefit him in figuring out downside areas within his fleet. Some of the analysis has been identified as to routine sort checks. Still, there might be an intensive vary of exams that may help in figuring out specific drawback standards throughout the system, which could not be clear by way of the everyday day-to-day evaluation normally performed.
Please see the ranking courses in TABLE 1
TABLE 1 FIG
TABLE 2 explains which oil analyses are really helpful and how often or under which circumstances.
TABLE 2 FIG
Oil sampling
The taking of the oil pattern is certainly one of the most important and important influencers within the evaluation outcome. If a pattern just isn’t taken to the prescribed procedure, then there’s a important chance that the analysis carried out, and the results acquired, are of no use.
เกจวัดแรงดันลมดิจิตอล should be taken to make sure quality management procedures are applied in each step of the sampling process as set out by worldwide requirements. A good high quality sample taken by applying the proper procedure is crucial. A sample could be contaminated by various elements, all of which can affect the result of the ends in a adverse manner.
All steps concerned in pattern taking must adhere to quality management procedures, including the container that is used, the sampling kit, the taking of the sample, the marking of the sample, the closing of the pattern, the storage and handling of the sample, and then the delivery of the pattern to the laboratory.
If the sample identification and pattern knowledge are handwritten, the human issue can result in incorrect interpretation of the data. The label must be caught 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 put in writing on the label must be oil- and waterproof. Otherwise, some information might be misplaced, making it extraordinarily troublesome for the laboratory personnel to finish the report or allocate the sample to a particular transformer.
Now, let’s discuss the forms of tests to discover out the transformer’s condition, the crucial values, and the beneficial actions in every case:
a) Colour and appearance
This is a routine inspection utilized to every oil sample.
When an oil sample arrives on the laboratory, one of the “tests” is a visible inspection of the oil pattern in a clear vessel to discover out the color, turbidity, and attainable particle identification.
Dark oils would possibly point out chemical degradation or contamination of the oil.
When there is a lot of turbidity, it might indicate a excessive water content within the oil.
If the drain valve was not wiped clean by the sampler, the filth particles in the drain valve could be incorporated into the sample. If particles are recognized as carbon, it’d point out a possible electrical fault in the unit. The DGA evaluation of the oil will verify if that is the case.
Clear oils with out contamination will point out a great situation, and no motion is recommended.
When oils are darkish or turbid, additional analysis will confirm any issues. The oil analysis outcomes 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 overseas particles, or each in the oil being analysed.
As the oil in transformers acts as an insulation medium to avoid flashover in the unit, the breakdown voltage should be excessive.
If the values are Good, it is strongly recommended to continue with the present sample interval motion plan.
If the values are Fair, more frequent sampling is recommended in collaboration with other parameter outcomes just like the water content material, 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 point out severe aging, the oil could be changed with new or reclaimed oil. Another choice can be to carry out on-site oil reclamation using a reclamation plant.
Reclamation of oil has the advantage that the color of the oil is restored, and the polar components are faraway from the oil. This process removes acid and water as nicely as some other compounds. Another advantage is that the oil could be re-used, and in most situations, this can be carried out without switching off the unit, which contributes to cost-saving. If unsure – as a substitute switch off the unit throughout this remedy process.
If the values are Poor, it is advisable to take motion as quickly as attainable and never delay the maintenance process. Excess water in the transformer system decreases the projected transformer lifetime considerably; extremely high water content could cause flashover within the unit, resulting in lack 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, besides class G
The outcomes of this test ought to all the time be thought-about at the facet of the breakdown power. If it is found that the water content is excessive and the breakdown strength is low, further motion must be taken. It is recommended that a second sample from the identical unit is tested to confirm the results.
In the case of switching gear, where there is not any paper current, the breakdown voltage is the figuring out issue.
It must be noted that the bounds indicated by IEC 60422 Edition 4 apply to transformers with operating temperatures between forty and 70 °C. If it is discovered that the unit’s operating temperature is exterior this temperature vary, it is best to check with Annex A of the standard.
When the worth obtained via analyses is GOOD, the traditional sampling interval could be maintained, requiring no additional motion.
When the worth returns a FAIR result, more frequent sampling is really helpful. It can additionally be useful to think about other parameters just like the breakdown voltage, particle content and DDF/resistivity, and acidity to decide on the motion to be carried out.
A POOR result would require immediate action from the asset supervisor. This would possibly embody taking one other pattern to confirm the outcomes from the primary evaluation. If it is confirmed that the water content material is high, the oil can be filtered; this process ought to take away a big portion of the moisture from the oil if applied correctly. Follow-up samples need to be taken to ensure that the moisture content material continues to be throughout the required limits. The cause is that probably the most significant portion of the water is caught up within the paper system within the transformer. This moisture will transfer from the paper into the oil under circumstances that favour this motion. It might be discovered later that the oil in the water has increased once more with none obvious cause, but the source can be the paper within the transformer.
A visible inspection is also really helpful to discover out if any water might move into the transformer or electrical gear by way of leaks. This problem could be extra severe if the transformer or electrical tools is outdoors 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.a hundred.10 to zero.25>0.20
C<0.100.15 to zero.30>0.30
F, G Not a routine take a look at
This is a routine check for all lessons besides F and G
The acids in oils are shaped as a result of 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’ll adversely affect the insulation properties of the oil and can increase paper degradation. If left untreated in transformers, this could result in sludge formation, normally around the lower parts of the transformer core. The sludge will ultimately type a semi-solid substance that is extremely difficult to remove.
If the result is GOOD, the common sampling interval can continue.
In case of a FAIR outcome, the sampling interval must be decreased to suit the situation. Future analysis ought to embody a visible 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 manager may determine to reclaim the oil or exchange it with new or reclaimed oil, whichever possibility would possibly go well with 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 zero.30>0.03
F, GNot a routine test
This is a routine test for all lessons of electrical tools, besides F and G
The dielectric dissipation issue or tan delta of this check 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 may influence the dissipation issue include water, dissolved insulating resin, and paper.
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 beneficial. The structure of the oil is damaged, in effect 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
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 assess the transformer insulation situation; this is primarily based on the fact that DC resistance is delicate to oil degradation.
When the result’s FAIR, extra frequent sampling and checking further parameters is really helpful.
When the result’s POOR, reclamation or an oil change is really helpful.
g) Inhibitor content percent
PropertyCategoryGoodFairPoor
Inhibitor Content %AllRestricted to Inhibited oils,Consult oil supplier40% to 60% Of original 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 relating to additives.
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 forestall oxygen from reacting with the oil. This considerably slows the getting older process within the oil and the strong insulation.
If the result’s FAIR, it is advised to top up the inhibitor degree to the prescribed level per provider directions. It is advised to use a area professional educated within the process to perform this task.
If the result obtained is POOR, the advice for this scenario would recommend that the tip person continues to use the oil “uninhibited,” but this may result in extra speedy degradation of both the liquid and solid insulation.
It should be famous that some transformers already have a built-in oil preservation system; this is designed to maintain dissolved oxygen at ranges beneath 1000ppm. This can be in 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 underneath these circumstances is not required, though it’d add additional protection against 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 secure, (rate of decrease < 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 referred to as metal deactivators, react with reactive steel surfaces and dissolved metals corresponding to copper and silver and cut back their rate of response with compounds within the oil. This consists of oxidation reactions with natural compounds and reactions with corrosive sulfur. Passivators are composed of two basic sorts, sulfur-based and nitrogen-based. The first advised 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 may deplete extra quickly; this depletion may speed up when the oil is un-inhibited.
With GOOD outcomes, common pattern intervals could be maintained.
With FAIR results, maintain regular monitoring.
When POOR, it’s advised to remove the oil or take away the source of corrosivity from the oil via particular oil remedy.
I) Sediment and sludge
This is not a routine take a look at.
It is advised that this test is performed when the oil results indicate a excessive acid value and the dissipation factor is near the unacceptable restrict.
The outcomes need to be less than 0.02% by mass to be negligible. If the outcomes return a value of more than 0.02% by mass, it is advised that it be reclaimed; otherwise, an oil change is beneficial.
j) Interfacial rigidity
This is not 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 test
F, GNot Applicable
The interfacial rigidity between transformer oil and water reduces during the aging process. What this implies in practical terms is there is extra polar compound present in the oil, decreasing the ability of an oil to function an insulator within the transformer system. There is a direct correlation between interfacial pressure and neutralisation number. Therefore, the interfacial rigidity turns into a quality criterion: the oil should be modified beneath a predefined restrict.
If results are GOOD, proceed the regular sampling interval.
If outcomes are FAIR, lower the sampling interval.
If results are POOR, verify the oil for sediment and/or sludge.
k) Corrosive sulfur
This isn’t a routine take a look at.
Oil is both corrosive or non-corrosive.
The presence of corrosive sulfur in transformer oil and its impact on the transformer system could be vital. The extent of the corrosion injury brought on by the sulfur could be so extreme that it would trigger failure of the gear if not checked. The addition of a copper passivator can reduce the influence of this compound on the transformer system.
In a research by Doble, it has been found that rubber merchandise used in transformers would possibly 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 mostly on this institute’s risk assessment 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 utilizing IEC 60970 [5]
m) Flashpoint ° C
Not a routine test
If there’s a most decrease in flashpoints by 10%, the gear might require further inspection. This value may differ in numerous countries.
It is advised to perform this test when an unusual odour is seen, the unit has been refilled, or an inner fault has occurred.
n) PCB (Polychlorinated Biphenyls)
This take a look at is not to determine the condition of the transformer; this could be a well being and security influence take a look at. PCB is hazardous to each people and the environment; it is important to check 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 chance of contamination is current. If PCB content material exceeds the beneficial limits, the appropriate action needs to be taken.
Units with a PCB content material of greater than 50ppm require a hearth security plan, environmental safety plan, and further precautionary measures when maintenance is finished. This oil needs to be changed, and the oil disposed of as hazardous waste, with a certificates of safe disposal issued to the gear proprietor.
Local regulatory our bodies define the bounds.
o) DGA (Dissolved Gas Analysis)
As DGA is an intricate science with lots of data and interpretation, we will talk about this phenomenon in part II of the article. The limits for the different gases and the interpretation of this knowledge based on worldwide standards will be discussed in detail, forming a part of the overall well being score determination of the transformer.
Conclusion
Transformer situation monitoring is an interlaced, extremely exciting subject of study. In this text, we focused on the kinds of checks to find out the condition of the transformer, the important values, and the beneficial 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 attainable to ensure best apply utility and optimised maintenance. It additionally make it easier to draw 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 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 power.”
6. Article initially printed 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 worked as laboratory manager for a serious industrial laboratory group, focusing on transformer well being. She has been intrigued by transformer chemistry right from the start of her profession, particularly in the analysis of check data. Corné has huge practical and theoretical knowledge of reliability maintenance programmes.
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