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 accumulating, measuring, recording, and evaluation of the relevant data concerning an asset’s operation. If we interpret the info accurately, it can give us nice insight into the asset’s situation.
Frequent monitoring of the asset may find yourself in much less maintenance required or extra prolonged intervals without any maintenance required.
It is crucial to establish the key parameters that are needed to give us an entire picture of the particular standing of the transformer and the motion we have to take to ensure the continued reliability of the asset to achieve the utmost lifetime.
What is the info telling us?
Has the situation of the unit modified because the last maintenance period?
Is it safe to function the unit?
Are there indicators of deterioration?
Is it protected to load the unit above the nameplate rating for a particular 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 think about replacement?
Are the recognized issues of a recurring nature?
Effective situation monitoring define
It is vitally necessary to determine clear objectives as part of your technique. What do you wish to achieve 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 might be a lot simpler to determine the required parameters.
Health indexing of assets is becoming a remarkable software in getting a clearer image of the situation of your transformer. Test parameters carry a numerical value-adding to the whole value of the Health Index Value of the transformer. pressure gauge ไฮ ด รอ ลิ ค had been calculated based mostly on the worldwide standards for mineral oils, indicating the critical values stipulated in the various standards.
The scope of oil analysis, interpretation of the info, and critical values
At the start of this section, it is essential to state that we deal with completely different dimension transformers in the industry. Transformers are divided into courses based on the kV scores of the gear. It is up to the reliability or asset manager to use the guidelines for bigger equipment, thereby implementing shorter increment oil evaluation and electrical exams.
The upkeep engineer or manager wants to discover out what sort of testing would profit him in identifying downside areas inside his fleet. Some of the evaluation has been recognized as to routine sort tests. Still, there might be an extensive vary of checks that may assist in identifying particular problem criteria throughout the system, which could not be clear through the standard day-to-day evaluation often carried out.
Please see the score lessons in TABLE 1
TABLE 1 FIG
TABLE 2 explains which oil analyses are beneficial and how typically or under which circumstances.
TABLE 2 FIG
Oil sampling
The taking of the oil sample is doubtless one of the most crucial and important influencers within the analysis consequence. If a sample is not taken to the prescribed procedure, then there is a significant risk that the analysis performed, and the results acquired, are of no use.
Care ought to be taken to ensure high quality control procedures are utilized in each step of the sampling course of as set out by international requirements. A good high quality pattern taken by applying the proper process is essential. A sample can be contaminated by numerous components, all of which can influence the outcome of the ends in a unfavorable manner.
All steps involved in sample taking should adhere to high quality control procedures, including the container that’s used, the sampling kit, the taking of the sample, the marking of the pattern, the closing of the pattern, the storage and dealing with of the sample, after which the delivery of the sample to the laboratory.
If the pattern identification and pattern data are handwritten, the human factor can lead to incorrect interpretation of the data. The label ought to 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 write on the label should be oil- and waterproof. Otherwise, some knowledge could be lost, making it extraordinarily troublesome for the laboratory personnel to complete the report or allocate the pattern to a specific transformer.
Now, let’s talk about the types of tests to find out the transformer’s condition, the important values, and the recommended actions in every case:
a) Colour and appearance
This is a routine inspection utilized to each oil pattern.
When an oil sample arrives on the laboratory, one of many “tests” is a visible inspection of the oil pattern in a clear vessel to determine the colour, turbidity, and attainable particle identification.
Dark oils would possibly indicate chemical degradation or contamination of the oil.
When there could be plenty of turbidity, it would 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 could be integrated into the pattern. If particles are recognized as carbon, it’d point out a potential electrical fault within the unit. The DGA evaluation of the oil will verify if that’s so.
Clear oils with out contamination will indicate a good situation, and no motion is beneficial.
When oils are dark or turbid, additional analysis will verify any issues. The oil analysis results may also determine the degree and kind 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 application
G <30
This is a routine inspection.
Breakdown voltage will point out the water content or the presence of foreign 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 must be excessive.
If the values are Good, it is suggested to continue with the present pattern interval action plan.
If the values are Fair, extra frequent sampling is really helpful in collaboration with other parameter results just like the water content material, DDF (dielectric dissipation factor), and acidity.
If values are Poor – it is strongly recommended to recondition the oil through oil reconditioning processes. If different checks indicate severe aging, the oil could be replaced with new or reclaimed oil. Another possibility 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 elements are removed from the oil. This course of removes acid and water as nicely as some other compounds. Another benefit is that the oil can be re-used, and in most conditions, this can be carried out without switching off the unit, which contributes to cost-saving. If doubtful – as an alternative change off the unit during this remedy process.
If the values are Poor, it is advisable to take action as soon as possible and not delay the upkeep course of. Excess water in the transformer system decreases the projected transformer lifetime significantly; extraordinarily high water content material can cause flashover within the unit, resulting in lack of the asset.
c) Water content material (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 test
This is a routine check for all lessons of electrical equipment, except class G
The outcomes of this check ought to all the time be considered along side the breakdown energy. If it is discovered that the water content is excessive and the breakdown power is low, further action needs to be taken. It is beneficial that a second pattern from the same unit is tested to verify the outcomes.
In the case of switching equipment, the place there is no paper current, the breakdown voltage is the determining factor.
It should be noted that the boundaries indicated by IEC 60422 Edition 4 apply to transformers with working temperatures between 40 and 70 °C. If it is found that the unit’s working temperature is outdoors this temperature range, it’s best to refer to Annex A of the standard.
When the value obtained through analyses is GOOD, the normal sampling interval could be maintained, requiring no additional motion.
When the value returns a FAIR result, more frequent sampling is beneficial. It is also helpful to suppose about other parameters like the breakdown voltage, particle content material and DDF/resistivity, and acidity to determine on the action to be implemented.
A POOR outcome will require instant motion from the asset manager. This may embrace taking one other pattern to confirm the outcomes from the first analysis. If it is confirmed that the water content material is high, the oil could be filtered; this process ought to remove a big portion of the moisture from the oil if applied correctly. Follow-up samples have to be taken to ensure that the moisture content material is still within the required limits. The purpose is that 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 conditions that favour this motion. It could be found later that the oil within the water has increased again with none obvious purpose, but the source could be the paper within the transformer.
A visible inspection can additionally be really helpful to determine if any water may transfer into the transformer or electrical tools through leaks. This problem could be extra severe if the transformer or electrical tools is exterior and never in a lined 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 0.25>0.20
C<0.100.15 to 0.30>0.30
F, G Not a routine test
This is a routine take a look at for all courses besides F and G
The acids in oils are shaped as a end result of 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 will improve paper degradation. If left untreated in transformers, this will result in sludge formation, often across the lower components of the transformer core. The sludge will eventually form a semi-solid substance that’s extremely troublesome to remove.
If the result is GOOD, the regular sampling interval can proceed.
In case of a FAIR result, the sampling interval ought to be decreased to suit the situation. Future analysis ought to include a visual inspection of the oil for sediment and sludge.
If the result’s POOR in accordance with the prescribed values in IEC 60422 Edition four.0, the asset supervisor might determine to reclaim the oil or exchange it with new or reclaimed oil, whichever possibility would possibly suit their necessities 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 test
This is a routine take a look at for all classes of electrical gear, except F and G
The dielectric dissipation issue or tan delta of this take a look at supplies info relating to the extent of the dielectric losses in transformer oil. This check measures the inefficiency of insulating materials.
When oil ages, we now have the formation of polar compounds, resulting in section displacement and dielectric losses. Other impurities that might influence the dissipation factor include water, dissolved insulating resin, and paper.
When the result’s FAIR, extra frequent sampling and checking additional parameters is beneficial.
When the result is POOR, reclamation or an oil change is beneficial. The construction of the oil is broken, in impact that the chemical bonds between the molecules have broken 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 test
DC resistivity of the oil is amongst the key parameters to evaluate the transformer insulation condition; that is based mostly on the truth that DC resistance is sensitive to oil degradation.
When the result is FAIR, extra frequent sampling and checking extra parameters is beneficial.
When the result’s POOR, reclamation or an oil change is really helpful.
g) Inhibitor content material %
PropertyCategoryGoodFairPoor
Inhibitor Content %AllRestricted to Inhibited oils,Consult oil supplier40% to 60% Of authentic value<40% of authentic worth
This take a look at 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 commonest oxidation inhibitors for transformer oils are 2,6-di-tertiary-butyl para-cresol (DBPC) and 2,6-di-tertiary butyl-phenol (DBP). The objective of the inhibitor is to forestall oxygen from reacting with the oil. This considerably slows the aging course of in the oil and the solid insulation.
If the result is FAIR, it’s advised to high up the inhibitor stage to the prescribed degree per provider directions. It is suggested to make use of a field professional trained within the process to perform this process.
If the result obtained is POOR, the advice for this state of affairs would suggest that the tip consumer continues to make use of the oil “uninhibited,” but this may lead to more rapid degradation of each the liquid and stable insulation.
It should be noted that some transformers already have a built-in oil preservation system; that is designed to maintain dissolved oxygen at ranges below 1000ppm. This could 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 under these circumstances isn’t required, though it would add additional safety 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 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 decreasing at >10mg/kg/year
Passivators, also referred to as steel deactivators, react with reactive metal surfaces and dissolved metals such as copper and silver and scale back their price of response with compounds within the oil. This contains 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 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 quickly; this depletion may speed up when the oil is un-inhibited.
With GOOD outcomes, regular pattern intervals may be maintained.
With FAIR results, maintain regular monitoring.
When POOR, it is advised to remove the oil or take away the supply of corrosivity from the oil via particular oil remedy.
I) Sediment and sludge
This is not a routine check.
It is suggested that this check is carried out when the oil results point out a high acid worth and the dissipation factor is close to the unacceptable limit.
The outcomes must be less than 0.02% by mass to be negligible. If the results return a value of greater than zero.02% by mass, it’s suggested that it be reclaimed; in any other case, an oil change is recommended.
j) Interfacial pressure
This is not a routine check
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 aging process. What this implies in practical terms is there’s extra polar compound current within the oil, reducing the ability of an oil to function an insulator in the transformer system. There is a direct correlation between interfacial tension and neutralisation quantity. Therefore, the interfacial tension becomes a top quality criterion: the oil should be changed under a predefined restrict.
If results are GOOD, continue the common sampling interval.
If results are FAIR, lower the sampling interval.
If outcomes are POOR, check 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 important. The extent of the corrosion injury brought on by the sulfur can be so severe that it would cause failure of the tools if not checked. The addition of a copper passivator can cut back the impression of this compound on the transformer system.
In a study by Doble, it has been discovered that rubber products used in transformers may add to the corrosivity of the oil. Nitrile rubber gaskets and hoses not permitted for oil filtration may contaminate the oil with corrosive sulfur.
CIGRE Brochure no 378, 2009 stipulates the need of corrective actions primarily based on this institute’s threat evaluation examine. [4]
l) Particle counting and sizing
Table three: 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 take a look at
If there is a maximum lower in flashpoints by 10%, the equipment may require further inspection. This value may differ in several nations.
It is advised to perform this check when an unusual odour is observed, the unit has been refilled, or an internal fault has occurred.
n) PCB (Polychlorinated Biphenyls)
This check is to not determine the situation of the transformer; this is a health and safety impact test. PCB is hazardous to both people and the setting; it is important to test for PCBs after the retro fill of a transformer. It is also required every time any maintenance has been done on the unit, and the potential of contamination is current. If PCB content material exceeds the really helpful limits, the appropriate motion must be taken.
Units with a PCB content of greater than 50ppm require a hearth safety plan, environmental protection plan, and extra precautionary measures when upkeep is finished. This oil must be replaced, and the oil disposed of as hazardous waste, with a certificate of secure disposal issued to the equipment proprietor.
Local regulatory our bodies define the boundaries.
o) DGA (Dissolved Gas Analysis)
As DGA is an intricate science with lots of data and interpretation, we are going to focus on this phenomenon partially II of the article. The limits for the different gases and the interpretation of this knowledge based on international standards shall be discussed in detail, forming part of the overall well being ranking willpower of the transformer.
Conclusion
Transformer situation monitoring is an interlaced, highly thrilling field of study. In this text, we focused on the types of exams to discover out the situation 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 specific date and time. This makes it attainable to make sure greatest follow utility and optimised upkeep. It additionally make it simpler to attract up a upkeep plan and action plan.
References:
1. IEC 60422 Edition 4.zero 2013-01 International Standard (Mineral insulating oils in electrical tools – supervision and upkeep guide)
2. Oxidation inhibitor and reinhabiting oil-filled transformers, by Andy Shkolnik
three. Passivators, what they’re 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 printed by Transformer Technology Magazine Issue sixteen – December 2021 https://www.transformer-technology.com
Author bio:
Corné Dames is a WearCheck transformer advisor. She has 20+ years’ experience in the trade, having beforehand worked as laboratory manager for a major industrial laboratory group, focusing on transformer health. She has been intrigued by transformer chemistry proper from the beginning of her profession, significantly in the analysis of test information. Corné has vast sensible and theoretical data of reliability upkeep programmes.
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