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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 collecting, measuring, recording, and analysis of the relevant data relating to an asset’s operation. If we interpret the information correctly, it may give us great insight into the asset’s condition.
Frequent monitoring of the asset can lead to less upkeep required or more prolonged durations with none upkeep required.
It is crucial to identify the necessary thing parameters which are wanted to provide us a whole picture of the actual standing of the transformer and the action we need to take to ensure the continued reliability of the asset to attain the maximum lifetime.
What is the data telling us?
Has the condition of the unit changed since the final upkeep period?
Is it secure to function the unit?
Are there signs of deterioration?
Is it protected to load the unit above the nameplate rating for a particular period?
Are we required to implement action to ensure the continued reliability of the unit?
How lengthy can we use the unit before we have to contemplate replacement?
Are the recognized issues of a recurring nature?
Effective situation monitoring outline
It is vitally important to determine clear targets as part of your strategy. What do you wish to obtain by implementing this situation monitoring plan? Is it in-service failure prevention? Or perhaps life extension? Maintenance deferral? By stipulating the end result and what you want to accomplish, it would be much simpler to determine the required parameters.
Health indexing of property is changing 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 worth of the Health Index Value of the transformer. These parameter weight values had been calculated based mostly on the international standards for mineral oils, indicating the crucial values stipulated within the numerous standards.
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 different dimension transformers within the trade. Transformers are divided into lessons based on the kV rankings of the gear. It is up to the reliability or asset manager to make use of the rules for bigger tools, thereby implementing shorter increment oil evaluation and electrical checks.
The maintenance engineer or manager needs to determine what sort of testing would profit him in figuring out problem areas within his fleet. Some of the analysis has been identified as to routine sort checks. Still, there’s an extensive range of checks that can help in figuring out specific downside criteria within the system, which might not be clear by way of the standard day-to-day analysis usually carried out.
Please see the rating courses in TABLE 1
TABLE 1 FIG
TABLE 2 explains which oil analyses are recommended and how usually or beneath which circumstances.
TABLE 2 FIG
Oil sampling
The taking of the oil sample is one of the most crucial and significant influencers in the analysis consequence. If a sample isn’t taken to the prescribed procedure, then there is a significant chance that the analysis performed, and the outcomes acquired, are of no use.
Care must be taken to make sure quality management procedures are applied in every step of the sampling course of as set out by international requirements. A good high quality sample taken by applying the proper procedure is essential. A sample can be contaminated by varied components, all of which may influence the end result of the results in a adverse method.
All steps involved in sample taking must adhere to quality management procedures, together with the container that’s used, the sampling equipment, the taking of the pattern, the marking of the pattern, the closing of the pattern, the storage and handling of the pattern, after which the supply of the pattern to the laboratory.
If the pattern identification and pattern information are handwritten, the human issue can result in incorrect interpretation of the data. The label should be caught onto the container to ensure no mix-ups in sample 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 should be oil- and water-resistant. Otherwise, some information may be misplaced, making it extremely troublesome 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 situation, the critical values, and the really helpful actions in every case:
a) Colour and appearance
This is a routine inspection utilized to every oil sample.
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 discover out the colour, turbidity, and attainable particle identification.
Dark oils would possibly indicate chemical degradation or contamination of the oil.
When there’s lots of turbidity, it might point out a high water content material in the oil.
If the drain valve was not wiped clean by the sampler, the dirt particles within the drain valve might be integrated into the pattern. If particles are identified as carbon, it would point out a possible electrical fault within the unit. The DGA analysis of the oil will affirm 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 affirm any problems. The oil evaluation outcomes may also decide the degree and sort 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 level application<40 kV for OLTC in delta or line-end software
G <30
This is a routine inspection.
Breakdown voltage will indicate the water content or the presence of international 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 have to be excessive.
If the values are Good, it is suggested to proceed with the current sample interval motion plan.
If the values are Fair, more frequent sampling is really helpful in collaboration with different parameter results 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 various exams indicate severe aging, the oil could be changed with new or reclaimed oil. Another option could be to perform 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 parts are removed from the oil. This process 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 accomplished with out switching off the unit, which contributes to cost-saving. If in doubt – as an alternative switch off the unit throughout this remedy process.
If the values are Poor, it’s advisable to take action as quickly as attainable and never delay the maintenance process. Excess water within the transformer system decreases the projected transformer lifetime significantly; extraordinarily high water content material may cause flashover in the unit, leading to lack of the asset.
c) Water content material (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 check
This is a routine check for all lessons of electrical equipment, except class G
The results of this check ought to all the time be thought of in conjunction with the breakdown energy. If it is discovered that the water content is high and the breakdown energy is low, additional motion needs to be taken. It is recommended that a second pattern from the same unit is examined to substantiate the outcomes.
In the case of switching gear, where there is not a paper current, the breakdown voltage is the figuring out factor.
It must be famous that the bounds indicated by IEC 60422 Edition 4 apply to transformers with working temperatures between forty and 70 °C. If it’s found that the unit’s working temperature is outside this temperature range, it’s best to refer to Annex A of the usual.
When the worth obtained through analyses is GOOD, the traditional sampling interval could be maintained, requiring no additional action.
When the value returns a FAIR outcome, more frequent sampling is really helpful. It can also be useful to contemplate different parameters just like the breakdown voltage, particle content material and DDF/resistivity, and acidity to decide on the action to be applied.
A POOR outcome would require quick action from the asset supervisor. This may include taking one other sample to substantiate the outcomes from the primary analysis. If it is confirmed that the water content material is excessive, the oil can be filtered; this process should take away a big portion of the moisture from the oil if applied correctly. Follow-up samples need to be taken to make certain that the moisture content continues to be within the required limits. The cause is that essentially 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 situations that favour this movement. It might be found later that the oil in the water has elevated once more without any obvious cause, but the supply would be the paper within the transformer.
A visual inspection can be beneficial to discover out if any water might transfer into the transformer or electrical tools through leaks. This downside might be more extreme 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.a hundred.10 to zero.15>0.15
B, E<0.100.10 to 0.25>0.20
C<0.one hundred.15 to zero.30>0.30
F, G Not a routine test
This is a routine check for all courses except F and G
The acids in oils are shaped due to chemical reactions between the oil, water, and paper. Higher temperatures or load will increase will assist in 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 increase paper degradation. If left untreated in transformers, this could result in sludge formation, normally across the lower components of the transformer core. The sludge will eventually type a semi-solid substance that’s extraordinarily troublesome to take away.
If the result’s GOOD, the regular sampling interval can proceed.
In case of a FAIR end result, the sampling interval ought to be decreased to fit the situation. Future evaluation ought to include a visible inspection of the oil for sediment and sludge.
If the result’s POOR based on the prescribed values in IEC 60422 Edition 4.0, the asset supervisor could determine to reclaim the oil or substitute it with new or reclaimed oil, whichever choice might 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.a hundred.10 to zero.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 check
This is a routine take a look at for all classes of electrical equipment, besides F and G
The dielectric dissipation factor or tan delta of this take a look at provides information relating to 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, leading to part displacement and dielectric losses. Other impurities that may affect the dissipation issue embrace water, dissolved insulating resin, and paper.
When the result is FAIR, extra frequent sampling and checking extra parameters is really helpful.
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 beneficial 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 check
DC resistivity of the oil is amongst the key parameters to assess the transformer insulation situation; that is based on the truth that DC resistance is delicate to grease degradation.
When the result’s FAIR, extra frequent sampling and checking further parameters is recommended.
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 original value<40% of unique worth
This check is restricted to oils with this additive.
It could be advisable to contact the oil provider to verify the small print relating to components.
The two commonest 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 aging course of in the oil and the stable insulation.
If the result’s FAIR, it’s suggested to high up the inhibitor stage to the prescribed level per supplier instructions. It is advised to use a subject skilled educated within the process to perform this process.
If the end result obtained is POOR, the advice for this situation would counsel that the tip consumer continues to use the oil “uninhibited,” however this will likely lead to extra fast degradation of both the liquid and solid insulation.
It ought to be famous that some transformers already have a built-in oil preservation system; that is designed to maintain dissolved oxygen at ranges under 1000ppm. This would be within the type 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 is not required, though it might add further protection towards 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 decrease of >10mg/kg/year<50 and decreasing at >10mg/kg/year
Passivators, also called steel deactivators, react with reactive metal surfaces and dissolved metals corresponding to copper and silver and scale back their rate of reaction with compounds within the oil. This contains oxidation reactions with organic 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 conscious, was in 1967 by J.J. Melchiore and I.W. Mills of the Sun Oil Company.[3]
As the oil ages, the passivator might deplete extra quickly; this depletion may speed up when the oil is un-inhibited.
With GOOD outcomes, common sample intervals may be maintained.
With FAIR outcomes, preserve common monitoring.
When POOR, it is suggested to take away the oil or remove the supply of corrosivity from the oil through special oil treatment.
I) Sediment and sludge
This just isn’t a routine test.
It is advised that this take a look at is performed when the oil outcomes indicate a excessive acid value and the dissipation factor is near the unacceptable limit.
The outcomes must be less than zero.02% by mass to be negligible. If the outcomes return a price of greater than zero.02% by mass, it is instructed that it be reclaimed; in any other case, an oil change is recommended.
j) Interfacial rigidity
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 pressure between transformer oil and water reduces through the growing older process. What this implies in practical terms is there may be more polar compound present in the oil, reducing the flexibility of an oil to serve as an insulator within the transformer system. There is a direct correlation between interfacial rigidity and neutralisation quantity. Therefore, the interfacial tension becomes a prime quality criterion: the oil must be modified below a predefined limit.
If results are GOOD, continue the regular 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 just 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 important. The extent of the corrosion injury brought on by the sulfur could be so extreme that it would cause failure of the tools if not checked. The addition of a copper passivator can reduce the impact of this compound on the transformer system.
In a research by Doble, it has been found that rubber merchandise used in transformers might 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 need of corrective actions based on this institute’s danger assessment research. [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 gear may require additional inspection. This value may differ in different countries.
It is advised to perform this take a look at when an uncommon 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 situation of the transformer; it is a well being and security impact check. PCB is hazardous to each humans and the surroundings; it is important to check for PCBs after the retro fill of a transformer. It can additionally be required every time any upkeep has been accomplished on the unit, and the risk of contamination is present. If PCB content material exceeds the recommended limits, the suitable motion needs to be taken.
Units with a PCB content of greater than 50ppm require a fireplace safety plan, environmental protection plan, and additional precautionary measures when maintenance is finished. This oil must be changed, and the oil disposed of as hazardous waste, with a certificates of protected disposal issued to the equipment proprietor.
Local regulatory our bodies define the bounds.
o) DGA (Dissolved Gas Analysis)
As DGA is an intricate science with plenty of knowledge and interpretation, we will talk about this phenomenon partly II of the article. The limits for the totally different gases and the interpretation of this knowledge according to worldwide standards might be discussed in detail, forming part of the overall well being score determination of the transformer.
Conclusion
Transformer condition monitoring is an interlaced, extremely thrilling field of research. In this article, we targeted on the types of checks to determine the situation of the transformer, the crucial values, and the recommended actions.
The Health Index indication makes it attainable to see the supposed reliability of a particular unit at a specific date and time. This makes it possible to ensure greatest apply utility and optimised maintenance. It additionally make it simpler to attract up a maintenance 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
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 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’ experience in the business, having beforehand labored as laboratory manager for a significant industrial laboratory group, specializing in transformer health. She has been intrigued by transformer chemistry proper from the start of her profession, notably within the evaluation of take a look at information. nuova fima pressure gauge ราคา has vast practical and theoretical knowledge of reliability upkeep programmes.
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