PETROL CHEMICALS
TALKING TRANSFORMER TESTING
by Brenna ShumbamhiniJune 9, 2022
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Introduction
Corne Dames
Condition monitoring is the frequent amassing, measuring, recording, and evaluation of the relevant data regarding an asset’s operation. If we interpret the information correctly, it can provide us nice insight into the asset’s situation.
Frequent monitoring of the asset can outcome in much less upkeep required or more extended periods with none upkeep required.
It is crucial to identify the key parameters which are wanted to offer us a complete picture of the particular standing of the transformer and the action we want to take to make sure the continued reliability of the asset to attain the maximum lifetime.
What is the data telling us?
Has the situation of the unit modified because the final maintenance period?
Is it protected to operate the unit?
Are there signs of deterioration?
Is it safe to load the unit above the nameplate score for a particular period?
Are we required to implement action to ensure the continued reliability of the unit?
How long can we use the unit before we need to think about replacement?
Are the identified problems of a recurring nature?
Effective condition monitoring define
It is vitally essential to identify clear objectives as part of your technique. What do you want to obtain by implementing this condition monitoring plan? Is it in-service failure prevention? Or perhaps life extension? Maintenance deferral? By stipulating the result and what you want to accomplish, it might be much easier to establish the required parameters.
Health indexing of assets is becoming a outstanding software 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 had been calculated primarily based on the international requirements for mineral oils, indicating the critical values stipulated within the numerous standards.
The scope of oil analysis, interpretation of the data, and important values
At the beginning of this part, it is essential to state that we cope with totally different measurement transformers within the business. Transformers are divided into courses based on the kV rankings of the equipment. It is as a lot as the reliability or asset supervisor to use the rules for bigger tools, thereby implementing shorter increment oil evaluation and electrical checks.
The upkeep engineer or supervisor wants to determine what sort of testing would benefit him in figuring out problem areas inside his fleet. Some of the analysis has been identified as to routine type exams. Still, there might be an extensive vary of exams that can assist in figuring out particular downside criteria inside the system, which could not be clear through the everyday day-to-day evaluation often carried out.
Please see the rating lessons in TABLE 1
TABLE 1 FIG
TABLE 2 explains which oil analyses are recommended and how often or underneath which circumstances.
TABLE 2 FIG
Oil sampling
The taking of the oil sample is amongst the most important and important influencers in the evaluation end result. If a pattern is not taken to the prescribed procedure, then there is a vital chance that the evaluation performed, and the outcomes 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 worldwide requirements. A good high quality pattern taken by applying the proper procedure is important. A pattern can be contaminated by various elements, all of which might affect the result of the ends in a negative manner.
All steps involved in pattern taking should adhere to high quality control procedures, together with the container that’s used, the sampling kit, the taking of the pattern, the marking of the sample, the closing of the pattern, the storage and dealing with of the sample, after which the supply of the pattern to the laboratory.
If the sample identification and sample information are handwritten, the human issue can lead to incorrect interpretation of the information. The label should 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 put in writing on the label must be oil- and water resistant. Otherwise, some data might be misplaced, making it extremely tough for the laboratory personnel to complete the report or allocate the sample to a specific transformer.
Now, let’s focus on the types of checks to find out the transformer’s situation, the important values, and the beneficial actions in each case:
a) Colour and appearance
This is a routine inspection applied to every oil pattern.
When an oil sample arrives on the laboratory, one of the “tests” is a visual inspection of the oil sample in a transparent vessel to determine the colour, turbidity, and possible particle identification.
Dark oils might point out chemical degradation or contamination of the oil.
When there could be plenty of turbidity, it might indicate a high water content within the oil.
If the drain valve was not cleaned by the sampler, the dirt particles in the drain valve may be integrated into the pattern. If particles are identified as carbon, it would point out a potential electrical fault within the unit. The DGA analysis of the oil will confirm if that is so.
Clear oils without contamination will point out a good situation, and no motion is recommended.
When oils are darkish or turbid, further evaluation will verify any problems. The oil evaluation 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 point application<40 kV for OLTC in delta or line-end utility
G <30
This is a routine inspection.
Breakdown voltage will point out the water content material 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 recommended to continue with the current sample interval action plan.
If the values are Fair, extra frequent sampling is really helpful in collaboration with different parameter results just like the water content material, DDF (dielectric dissipation factor), and acidity.
If values are Poor – it is recommended to recondition the oil by way of oil reconditioning processes. If alternative tests indicate severe growing older, the oil can be changed with new or reclaimed oil. Another possibility can 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 parts are removed from the oil. This process removes acid and water as properly as some other compounds. Another benefit is that the oil can be re-used, and in most situations, this might be carried out with out switching off the unit, which contributes to cost-saving. If doubtful – as a substitute switch off the unit during this treatment course of.
If the values are Poor, it’s advisable to take motion as quickly as possible and not delay the upkeep process. Excess water within the transformer system decreases the projected transformer lifetime considerably; extremely excessive water content can cause flashover within the unit, leading to lack 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 take a look at
This is a routine take a look at for all lessons of electrical tools, besides class G
The results of this test should always be thought of in conjunction with the breakdown power. If it’s discovered that the water content is high and the breakdown strength is low, further action needs to be taken. It is really helpful that a second pattern from the identical unit is tested to substantiate the results.
In the case of switching equipment, the place there is no paper current, the breakdown voltage is the figuring out issue.
It must be noted that the boundaries indicated by IEC 60422 Edition 4 apply to transformers with working temperatures between forty and 70 °C. If it’s discovered that the unit’s working temperature is exterior this temperature range, it is best to discuss with Annex A of the standard.
When the worth obtained by way of analyses is GOOD, the conventional sampling interval can be maintained, requiring no further action.
When the value returns a FAIR outcome, more frequent sampling is really helpful. It can be useful to suppose about different parameters like the breakdown voltage, particle content and DDF/resistivity, and acidity to decide on the motion to be carried out.
A POOR outcome will require instant action from the asset manager. This might embody taking another pattern to confirm the outcomes from the first evaluation. If it’s confirmed that the water content is high, the oil could be filtered; this process should take away a large portion of the moisture from the oil if applied correctly. Follow-up samples have to be taken to ensure that the moisture content continues to be 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 movement. It may be discovered later that the oil in the water has increased again without any obvious purpose, however the supply could be the paper within the transformer.
A visual inspection can also be really helpful to determine if any water may move into the transformer or electrical equipment via leaks. This problem may be more extreme if the transformer or electrical equipment is outside and not in a lined space.
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<0.100.15 to 0.30>0.30
F, G Not a routine test
This is a routine test for all classes except F and G
The acids in oils are formed as a end result 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 will lead to sludge formation, usually around the lower components of the transformer core. The sludge will finally type a semi-solid substance that’s extraordinarily tough to take away.
If the result’s GOOD, the regular sampling interval can continue.
In case of a FAIR end result, the sampling interval ought to be decreased to fit the state of affairs. Future evaluation should embrace a visual inspection of the oil for sediment and sludge.
If the result is POOR in accordance with the prescribed values in IEC 60422 Edition four.zero, the asset manager might determine to reclaim the oil or replace it with new or reclaimed oil, whichever possibility would possibly swimsuit 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.one hundred.10 to zero.20>0.20
B, C<0.a hundred.10 to 0.50>0.50
D<0.010.01 to 0.03>0.03
E<0.one hundred.01 to 0.30>0.03
F, GNot a routine check
This is a routine check for all courses of electrical gear, except F and G
The dielectric dissipation factor or tan delta of this take a look at supplies information regarding the extent of the dielectric losses in transformer oil. This test measures the inefficiency of insulating material.
When oil ages, we’ve the formation of polar compounds, leading to phase displacement and dielectric losses. Other impurities which may affect the dissipation issue embody water, dissolved insulating resin, and paper.
When the result’s FAIR, more frequent sampling and checking additional parameters is recommended.
When the result is POOR, reclamation or an oil change is beneficial. The structure of the oil is broken, in impact that the chemical bonds between the molecules have broken 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 considered one of the key parameters to assess the transformer insulation situation; that is based on the fact that DC resistance is delicate to grease degradation.
When the result is FAIR, more frequent sampling and checking additional parameters is beneficial.
When the result is POOR, reclamation or an oil change is really helpful.
g) Inhibitor content material percent
PropertyCategoryGoodFairPoor
Inhibitor Content %AllRestricted to Inhibited oils,Consult oil supplier40% to 60% Of original value<40% of authentic worth
This check is restricted to oils with this additive.
It could be advisable to contact the oil supplier to confirm the details concerning additives.
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 function 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 advised to high up the inhibitor degree to the prescribed degree per provider instructions. It is suggested to make use of a subject professional educated in the process to perform this task.
If the end result obtained is POOR, the advice for this state of affairs would suggest that the top consumer continues to use the oil “uninhibited,” however this will result in extra rapid degradation of each the liquid and stable insulation.
It should be famous that some transformers already have a built-in oil preservation system; that is designed to keep dissolved oxygen at levels under 1000ppm. This could be in the form of a nitrogen system, a nitrogen tank or generator, or a conservator tank geared up with a rubber diaphragm (bladder). Using inhibited oils under these circumstances just isn’t required, although it would add further 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 secure, (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 metallic deactivators, react with reactive metallic surfaces and dissolved metals similar 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 basic types, sulfur-based and nitrogen-based. The first suggested 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 may accelerate when the oil is un-inhibited.
With GOOD results, regular sample intervals may be maintained.
With FAIR outcomes, keep common monitoring.
When POOR, it’s suggested to remove the oil or remove the supply of corrosivity from the oil through special oil therapy.
I) Sediment and sludge
This just isn’t a routine test.
It is advised that this check is performed when the oil outcomes indicate a excessive acid worth and the dissipation factor is close to the unacceptable limit.
The results must be lower than 0.02% by mass to be negligible. If the outcomes return a price of more than 0.02% by mass, it’s suggested that it’s reclaimed; otherwise, an oil change is recommended.
j) Interfacial rigidity
This is not 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 check
F, GNot Applicable
The interfacial pressure between transformer oil and water reduces in the course of the aging process. What this means in sensible terms is there is more polar compound current in the oil, decreasing the flexibility of an oil to serve as an insulator within the transformer system. There is a direct correlation between interfacial tension and neutralisation quantity. Therefore, the interfacial tension becomes a quality criterion: the oil must be changed below a predefined limit.
If results are GOOD, continue the regular sampling interval.
If results 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 check.
Oil is both corrosive or non-corrosive.
The presence of corrosive sulfur in transformer oil and its effect on the transformer system can be vital. The extent of the corrosion harm brought on by the sulfur can be so severe that it’d trigger failure of the gear if not checked. The addition of a copper passivator can scale back the impact of this compound on the transformer system.
In a research by Doble, it has been found that rubber products utilized in transformers may add to the corrosivity of the oil. Nitrile rubber gaskets and hoses not permitted for oil filtration would possibly contaminate the oil with corrosive sulfur.
CIGRE Brochure no 378, 2009 stipulates the need of corrective actions based on this institute’s risk assessment examine. [4]
l) Particle counting and sizing
Table 3: 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 check
If there’s a maximum decrease in flashpoints by 10%, the gear may require further inspection. This value may differ in numerous countries.
It is advised to perform this take a look at when an uncommon odour is noticed, the unit has been refilled, or an inside fault has occurred.
n) PCB (Polychlorinated Biphenyls)
This test is to not determine the condition of the transformer; this could be a health and security impression take a look at. PCB is hazardous to each humans and the setting; it is important to check for PCBs after the retro fill of a transformer. It can additionally be required each time any upkeep has been carried out on the unit, and the potential of contamination is current. If PCB content exceeds the really helpful limits, the appropriate motion needs to be taken.
Units with a PCB content of more than 50ppm require a fireplace security plan, environmental protection plan, and further precautionary measures when upkeep is done. This oil needs to be changed, and the oil disposed of as hazardous waste, with a certificate of secure disposal issued to the gear proprietor.
Local regulatory bodies define the bounds.
o) DGA (Dissolved Gas Analysis)
As DGA is an intricate science with plenty of information and interpretation, we are going to discuss this phenomenon partly II of the article. The limits for the completely different gases and the interpretation of this data according to worldwide standards shall be mentioned intimately, forming part of the overall well being rating dedication of the transformer.
Conclusion
Transformer situation monitoring is an interlaced, extremely thrilling area of study. In this article, we centered on the forms of tests to find out the condition of the transformer, the crucial values, and the beneficial actions.
The Health Index indication makes it possible to see the supposed reliability of a selected unit at a particular date and time. This makes it potential to ensure best follow application and optimised maintenance. เกรดวัดแรงดัน make it easier to attract up a maintenance plan and action plan.
References:
1. IEC 60422 Edition 4.0 2013-01 International Standard (Mineral insulating oils in electrical tools – supervision and maintenance 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 published by Transformer Technology Magazine Issue 16 – December 2021 https://www.transformer-technology.com
Author bio:
Corné Dames is a WearCheck transformer consultant. She has 20+ years’ expertise in the industry, having beforehand worked as laboratory manager for a significant industrial laboratory group, focusing on transformer well being. She has been intrigued by transformer chemistry proper from the beginning of her career, notably in the analysis of check knowledge. Corné has vast practical and theoretical knowledge of reliability upkeep programmes.
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