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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 evaluation of the relevant information concerning an asset’s operation. If we interpret the information appropriately, it can provide us great perception into the asset’s situation.
Frequent monitoring of the asset can result in much less upkeep required or extra prolonged durations without any upkeep required.
It is essential to establish the important thing parameters which might be needed to give us an entire picture of the particular standing of the transformer and the motion we have to take to make sure the continued reliability of the asset to realize the utmost lifetime.
What is the data telling us?
Has the situation of the unit changed since the final upkeep period?
Is it secure to function the unit?
Are there signs of deterioration?
Is it safe to load the unit above the nameplate rating for a specific period?
Are we required to implement action to make sure the continued reliability of the unit?
How lengthy can we use the unit earlier than we have to think about replacement?
Are the identified problems of a recurring nature?
Effective situation monitoring outline
It is vitally essential to identify clear objectives as a half of your strategy. What do you wish to achieve by implementing this situation monitoring plan? Is it in-service failure prevention? Or maybe life extension? Maintenance deferral? By stipulating the outcome and what you wish to accomplish, it would be much simpler to determine the required parameters.
Health indexing of property is changing into a remarkable tool in getting a clearer picture 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. These parameter weight values had been calculated based mostly on the international standards for mineral oils, indicating the important values stipulated within the various standards.
The scope of oil analysis, interpretation of the information, and important values
At the start of this section, it is important to state that we cope with totally different size transformers within the industry. Transformers are divided into lessons based on the kV ratings of the gear. It is as much as the reliability or asset supervisor to make use of the guidelines for bigger gear, thereby implementing shorter increment oil evaluation and electrical tests.
The upkeep engineer or supervisor wants to discover out what sort of testing would profit him in identifying downside areas inside his fleet. Some of the analysis has been identified as to routine type checks. Still, there is an intensive range of exams that may assist in figuring out particular problem criteria throughout the system, which could not be clear via the everyday day-to-day analysis usually 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 considered one of the most vital and significant influencers within the evaluation outcome. If a pattern just isn’t taken to the prescribed process, then there is a significant chance that the analysis carried out, and the outcomes acquired, are of no use.
Care should be taken to ensure quality control procedures are utilized in every step of the sampling process as set out by international standards. A good high quality pattern taken by making use of the proper process is important. A pattern could be contaminated by varied factors, all of which might influence the end result of the results in a unfavorable method.
All steps concerned in pattern taking must adhere to quality control procedures, together with the container that’s used, the sampling package, the taking of the pattern, 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 knowledge are handwritten, the human issue can lead to incorrect interpretation of the info. The label ought to be stuck onto the container to ensure 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 write on the label must be oil- and water-resistant. Otherwise, some information might be misplaced, making it extraordinarily troublesome for the laboratory personnel to complete the report or allocate the pattern to a particular transformer.
Now, let’s discuss the kinds of checks to determine the transformer’s situation, the critical values, and the really helpful actions in each case:
a) Colour and appearance
This is a routine inspection applied to every oil pattern.
When an oil pattern arrives on the laboratory, one of the “tests” is a visible inspection of the oil pattern in a transparent vessel to discover out the colour, turbidity, and possible particle identification.
Dark oils may point out chemical degradation or contamination of the oil.
When there could be lots of turbidity, it might indicate a high water content material in the oil.
If the drain valve was not cleaned by the sampler, the dirt particles within the drain valve may be integrated into the pattern. If particles are recognized as carbon, it’d point out a possible electrical fault in the unit. The DGA analysis of the oil will affirm if that is so.
Clear oils with out contamination will point out an excellent condition, and no motion is really helpful.
When oils are darkish or turbid, further analysis will verify any issues. The oil analysis results may even determine the degree 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 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 material 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 within the unit, the breakdown voltage should be high.
If the values are Good, it is strongly recommended to proceed with the present sample interval motion plan.
If the values are Fair, extra frequent sampling is really helpful in collaboration with other parameter results just like the water content, DDF (dielectric dissipation factor), and acidity.
If values are Poor – it is recommended to recondition the oil via oil reconditioning processes. If various checks indicate extreme getting older, the oil can be changed with new or reclaimed oil. Another option would be to perform on-site oil reclamation utilizing a reclamation plant.
Reclamation of oil has the benefit that the color of the oil is restored, and the polar elements are removed from the oil. This course of removes acid and water as well as another compounds. Another advantage is that the oil could be re-used, and in most conditions, this could be done without switching off the unit, which contributes to cost-saving. If in doubt – as a substitute change off the unit throughout this treatment course of.
If the values are Poor, it’s advisable to take motion as quickly as potential and never delay the upkeep course of. Excess water within the transformer system decreases the projected transformer lifetime considerably; extraordinarily high water content material can cause flashover within the unit, resulting in loss 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 take a look at
This is a routine take a look at for all courses of electrical equipment, besides class G
The results of this take a look at should all the time be thought-about at the aspect of the breakdown power. If it is found that the water content is excessive and the breakdown energy is low, additional motion must be taken. It is recommended that a second sample from the same unit is examined to verify the outcomes.
In the case of switching equipment, where there isn’t any paper current, the breakdown voltage is the figuring out factor.
It ought to be famous that the bounds indicated by IEC 60422 Edition four apply to transformers with working temperatures between forty and 70 °C. If it’s found that the unit’s operating temperature is outdoors this temperature vary, it’s best to check with Annex A of the usual.
When the worth obtained through analyses is GOOD, the conventional sampling interval may be maintained, requiring no additional action.
When the worth returns a FAIR outcome, extra frequent sampling is really helpful. It can additionally be helpful to assume about different parameters just like the breakdown voltage, particle content and DDF/resistivity, and acidity to decide on the action to be carried out.
A POOR end result would require quick action from the asset supervisor. This may embrace taking another sample to substantiate the results from the primary analysis. If it’s confirmed that the water content material is high, the oil can be filtered; this course of should take away a big portion of the moisture from the oil if utilized accurately. Follow-up samples must be taken to make sure that the moisture content material is still within the required limits. The reason is that probably the most good portion of the water is caught up in the paper system in the transformer. This moisture will transfer from the paper into the oil under conditions that favour this motion. It may be discovered later that the oil within the water has elevated once more with none apparent purpose, however the source can be the paper in the transformer.
A visible inspection can additionally be beneficial to determine if any water would possibly move into the transformer or electrical gear through leaks. This downside could be extra extreme if the transformer or electrical equipment is exterior and not in a covered space.
d) Acidity (mgKOH/g oil) Neutralization Number
PropertyCategoryGoodFairPoor
Acidity mgKOH/g oilO, A, D<0.100.10 to 0.15>0.15
B, E<0.a hundred.10 to zero.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 as a result of chemical reactions between the oil, water, and paper. เกจวัดแรงดันปั๊มลม or load increases will assist in the formation of the acids. Because acids are polar compounds, it’s going to adversely affect the insulation properties of the oil and can enhance paper degradation. If left untreated in transformers, this could result in sludge formation, often around the decrease components of the transformer core. The sludge will finally type a semi-solid substance that’s extraordinarily troublesome to take away.
If the result is GOOD, the common sampling interval can proceed.
In case of a FAIR result, the sampling interval ought to be decreased to suit the situation. Future evaluation should embrace a visible inspection of the oil for sediment and sludge.
If the result is POOR according to the prescribed values in IEC 60422 Edition 4.0, the asset supervisor might resolve to reclaim the oil or replace it with new or reclaimed oil, whichever possibility 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<0.100.10 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.a hundred.01 to 0.30>0.03
F, GNot a routine test
This is a routine check for all lessons of electrical gear, besides F and G
The dielectric dissipation issue or tan delta of this take a look at provides info relating to the extent of the dielectric losses in transformer oil. This check measures the inefficiency of insulating material.
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 embody water, dissolved insulating resin, and paper.
When the result is FAIR, more frequent sampling and checking extra parameters is beneficial.
When the result is POOR, reclamation or an oil change is recommended. The structure 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 one of the key parameters to evaluate the transformer insulation condition; this is based mostly on the reality that DC resistance is sensitive to grease degradation.
When the result’s FAIR, extra frequent sampling and checking additional parameters is really helpful.
When the result’s POOR, reclamation or an oil change is recommended.
g) Inhibitor content material %
PropertyCategoryGoodFairPoor
Inhibitor Content %AllRestricted to Inhibited oils,Consult oil supplier40% to 60% Of authentic value<40% of unique value
This check is restricted to oils with this additive.
It could be advisable to contact the oil supplier to confirm the details 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 function of the inhibitor is to stop oxygen from reacting with the oil. This considerably slows the getting older course of within the oil and the solid insulation.
If the result’s FAIR, it is advised to prime up the inhibitor level to the prescribed level per supplier directions. It is suggested to use a area professional skilled within the procedure to carry out this task.
If the result obtained is POOR, the recommendation for this situation would recommend that the tip user continues to use the oil “uninhibited,” but this may lead to extra rapid degradation of each the liquid and stable insulation.
เกจวัดความดันแก๊ส ought to be famous that some transformers have already got a built-in oil preservation system; this is designed to maintain dissolved oxygen at levels below 1000ppm. This would be in the type of a nitrogen system, a nitrogen tank or generator, or a conservator tank outfitted with a rubber diaphragm (bladder). Using inhibited oils underneath these circumstances just isn’t required, although it would add extra 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 reducing at >10mg/kg/year
Passivators, also recognized as steel deactivators, react with reactive steel surfaces and dissolved metals similar to copper and silver and scale back their rate of response with compounds within the oil. This includes oxidation reactions with natural compounds and reactions with corrosive sulfur. Passivators are composed of two fundamental varieties, sulfur-based and nitrogen-based. The first instructed 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 may deplete more rapidly; this depletion might accelerate when the oil is un-inhibited.
With GOOD results, regular pattern intervals may be maintained.
With FAIR outcomes, keep common monitoring.
When POOR, it is suggested to take away the oil or take away the supply of corrosivity from the oil via special oil treatment.
I) Sediment and sludge
This just isn’t a routine test.
It is advised that this test is carried out when the oil results point out a high acid worth and the dissipation issue is close to the unacceptable limit.
The results need to be less than zero.02% by mass to be negligible. If the results return a price of greater than 0.02% by mass, it is instructed that or not it’s reclaimed; in any other case, an oil change is beneficial.
j) Interfacial tension
This is not a routine take a look at
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 tension between transformer oil and water reduces through the getting older process. What this means in sensible terms is there might be extra polar compound current in the oil, lowering the power of an oil to function an insulator in the transformer system. There is a direct correlation between interfacial rigidity and neutralisation quantity. Therefore, the interfacial rigidity turns into a high quality criterion: the oil should be modified below a predefined limit.
If results are GOOD, continue the common sampling interval.
If results are FAIR, decrease the sampling interval.
If results are POOR, verify the oil for sediment and/or sludge.
k) Corrosive sulfur
This just isn’t a routine check.
Oil is both corrosive or non-corrosive.
The presence of corrosive sulfur in transformer oil and its impact on the transformer system can be vital. The extent of the corrosion damage caused by the sulfur can be so extreme that it might 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 examine 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 necessity of corrective actions based on this institute’s risk assessment 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 utilizing IEC 60970 [5]
m) Flashpoint ° C
Not a routine test
If there’s a maximum lower in flashpoints by 10%, the gear might require further inspection. This worth may differ in several nations.
It is advised to carry out this take a look at when an uncommon odour is observed, the unit has been refilled, or an inside fault has occurred.
n) PCB (Polychlorinated Biphenyls)
This test is not to decide the condition of the transformer; it is a health and safety influence test. PCB is hazardous to both people and the environment; it is important to test for PCBs after the retro fill of a transformer. It can be required whenever any maintenance has been accomplished on the unit, and the potential for contamination is present. If PCB content material exceeds the recommended limits, the suitable action needs to be taken.
Units with a PCB content material of greater than 50ppm require a fireplace security plan, environmental protection plan, and extra precautionary measures when maintenance is done. 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 boundaries.
o) DGA (Dissolved Gas Analysis)
As DGA is an intricate science with lots of knowledge and interpretation, we’ll focus on this phenomenon partly II of the article. The limits for the different gases and the interpretation of this data in accordance with international standards might be discussed intimately, forming part of the general health score dedication of the transformer.
Conclusion
Transformer situation monitoring is an interlaced, extremely thrilling subject of research. In this text, we targeted on the types of tests to determine the condition of the transformer, the critical values, and the beneficial actions.
The Health Index indication makes it attainable to see the supposed reliability of a selected unit at a particular date and time. This makes it potential to ensure best practice software and optimised maintenance. It also make it easier to attract up a maintenance plan and motion plan.
References:
1. IEC 60422 Edition 4.0 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 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 strength.”
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 supervisor for a significant industrial laboratory group, specializing in transformer well being. She has been intrigued by transformer chemistry right from the beginning of her profession, significantly in the analysis of check data. Corné has huge sensible and theoretical information of reliability upkeep programmes.
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