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 related knowledge concerning an asset’s operation. If we interpret the info appropriately, it can provide us great insight into the asset’s condition.
Frequent monitoring of the asset can result in less upkeep required or extra prolonged periods with none maintenance required.
It is crucial to establish the key parameters which may be needed to provide us a whole image of the actual standing of the transformer and the motion we have to take to make sure the continued reliability of the asset to attain the maximum lifetime.
What is the information telling us?
Has the condition of the unit changed since the final maintenance period?
Is it protected to operate the unit?
Are there signs of deterioration?
Is it secure to load the unit above the nameplate score for a specific period?
Are we required to implement motion to ensure the continued reliability of the unit?
How lengthy can we use the unit earlier than we have to contemplate replacement?
Are the recognized issues of a recurring nature?
Effective condition monitoring define
It is vitally necessary to determine clear objectives as a part of your technique. What do you want to achieve by implementing this situation monitoring plan? Is it in-service failure prevention? Or possibly life extension? Maintenance deferral? By stipulating the result and what you wish to accomplish, it might be much simpler to establish the required parameters.
Health indexing of assets is turning into a exceptional device in getting a clearer image of the condition of your transformer. Test parameters carry a numerical value-adding to the entire value of the Health Index Value of the transformer. These parameter weight values have been calculated primarily based on the international requirements for mineral oils, indicating the crucial values stipulated within the various requirements.
The scope of oil analysis, interpretation of the info, and significant values
At the beginning of this section, it’s important to state that we cope with completely different measurement transformers in the industry. Transformers are divided into lessons based on the kV scores of the equipment. pressure gauge ลม is up to the reliability or asset supervisor to make use of the rules for bigger equipment, thereby implementing shorter increment oil evaluation and electrical checks.
The maintenance engineer or manager wants to determine what kind of testing would profit him in identifying problem areas inside his fleet. Some of the analysis has been recognized as to routine sort tests. Still, there might be an intensive range of tests that can help in identifying particular problem standards within the system, which might not be clear through the standard day-to-day evaluation often carried out.
Please see the score classes in TABLE 1
TABLE 1 FIG
TABLE 2 explains which oil analyses are beneficial and how typically or underneath which circumstances.
TABLE 2 FIG
Oil sampling
The taking of the oil sample is one of the most crucial and critical influencers within the analysis outcome. If a pattern is not taken to the prescribed procedure, then there’s a vital possibility that the evaluation carried out, and the results acquired, are of no use.
Care should be taken to make sure high quality management 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 important. A pattern can be contaminated by numerous elements, all of which might affect the result of the ends in a negative method.
All steps involved in sample taking should adhere to high quality management procedures, together with 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 dealing with of the sample, after which the supply of the pattern to the laboratory.
If the sample identification and pattern data are handwritten, the human factor can result in incorrect interpretation of the data. The label must be caught onto the container to make sure 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 ought to be oil- and water-resistant. Otherwise, some knowledge may be lost, making it extraordinarily difficult for the laboratory personnel to complete the report or allocate the pattern to a specific transformer.
Now, let’s talk about the types of checks to determine the transformer’s condition, the important values, and the really helpful actions in each case:
a) Colour and look
This is a routine inspection utilized to each oil sample.
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 determine the color, turbidity, and possible particle identification.
Dark oils might point out chemical degradation or contamination of the oil.
When there is a lot of turbidity, it would indicate a high water content in the oil.
If the drain valve was not wiped clean by the sampler, the dirt particles within the drain valve might be incorporated into the pattern. If particles are recognized as carbon, it’d point out a potential electrical fault in the unit. The DGA analysis of the oil will verify if that is the case.
Clear oils with out contamination will indicate a good situation, and no action is really helpful.
When oils are darkish or turbid, additional evaluation will affirm any problems. The oil analysis outcomes will also decide the diploma and kind 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 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 within the oil being analysed.
As the oil in transformers acts as an insulation medium to keep away from flashover in the unit, the breakdown voltage should be excessive.
If the values are Good, it is suggested to continue with the present pattern interval action 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 through oil reconditioning processes. If various tests point out extreme growing older, the oil may be changed with new or reclaimed oil. Another option would be to carry out on-site oil reclamation utilizing a reclamation plant.
Reclamation of oil has the advantage that the color of the oil is restored, and the polar elements are faraway from the oil. This process removes acid and water as nicely as another compounds. Another benefit is that the oil could be re-used, and in most conditions, this can be carried out with out switching off the unit, which contributes to cost-saving. If doubtful – instead switch off the unit during this therapy 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 in the transformer system decreases the projected transformer lifetime considerably; extremely high water content material can cause flashover within 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 test
This is a routine take a look at for all courses of electrical equipment, except class G
The results of this take a look at should always be thought-about in conjunction with the breakdown power. If it is found that the water content is high and the breakdown energy is low, additional action must be taken. It is recommended that a second sample from the same unit is examined to substantiate the results.
In the case of switching tools, where there isn’t a paper present, the breakdown voltage is the determining issue.
It should be noted that the bounds indicated by IEC 60422 Edition four apply to transformers with working temperatures between forty and 70 °C. If it is found that the unit’s working temperature is outdoors this temperature range, it is best to refer to Annex A of the standard.
When the value obtained by way of analyses is GOOD, the traditional sampling interval could be maintained, requiring no further action.
When the value returns a FAIR end result, extra frequent sampling is really helpful. It is also helpful to consider 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 outcome would require immediate motion from the asset manager. This may embrace taking one other pattern to substantiate the outcomes from the first analysis. If it is 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 utilized appropriately. Follow-up samples must be taken to guarantee that the moisture content continues to be inside the required limits. The cause is that 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 beneath situations that favour this motion. It could be discovered later that the oil within the water has elevated once more without any apparent reason, however the supply can be the paper in the transformer.
A visual inspection is also recommended to determine if any water would possibly transfer into the transformer or electrical gear by way of leaks. This drawback could be more severe if the transformer or electrical equipment is outdoors and not in a coated area.
d) Acidity (mgKOH/g oil) Neutralization Number
PropertyCategoryGoodFairPoor
Acidity mgKOH/g oilO, A, D<0.one hundred.10 to zero.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 test
This is a routine test for all lessons besides F and G
The acids in oils are formed as a 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 result in sludge formation, often around the lower components of the transformer core. The sludge will finally kind a semi-solid substance that’s extremely difficult to remove.
If the result’s GOOD, the common sampling interval can proceed.
In case of a FAIR end result, the sampling interval must be decreased to suit the scenario. Future evaluation ought to embrace a visual inspection of the oil for sediment and sludge.
If the result’s POOR according to the prescribed values in IEC 60422 Edition 4.zero, the asset supervisor might decide to reclaim the oil or exchange it with new or reclaimed oil, whichever choice might go well with 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<0.100.10 to zero.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 take a look at
This is a routine take a look at for all lessons of electrical equipment, except F and G
The dielectric dissipation issue or tan delta of this take a look at supplies info regarding the extent of the dielectric losses in transformer oil. This check measures the inefficiency of insulating materials.
When oil ages, we have the formation of polar compounds, resulting in phase displacement and dielectric losses. Other impurities which may influence the dissipation factor embrace water, dissolved insulating resin, and paper.
When the result’s FAIR, extra frequent sampling and checking additional parameters is really helpful.
When the result is POOR, reclamation or an oil change is recommended. The construction of the oil is broken, in effect that the chemical bonds between the molecules have damaged 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 check
DC resistivity of the oil is probably certainly one of the key parameters to evaluate the transformer insulation condition; this is based on the reality that DC resistance is delicate to oil degradation.
When the result’s FAIR, extra frequent sampling and checking additional parameters is recommended.
When the result’s POOR, reclamation or an oil change is really helpful.
g) Inhibitor content %
PropertyCategoryGoodFairPoor
Inhibitor Content %AllRestricted to Inhibited oils,Consult oil supplier40% to 60% Of authentic value<40% of original value
This test is restricted to oils with this additive.
It would be advisable to contact the oil provider to verify the major points concerning additives.
The two commonest 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 objective of the inhibitor is to prevent oxygen from reacting with the oil. This significantly slows the growing older process within the oil and the strong insulation.
If the result’s FAIR, it’s suggested to prime up the inhibitor level to the prescribed degree per supplier directions. It is suggested to use a field skilled trained within the procedure to perform this task.
If the result obtained is POOR, the recommendation for this situation would recommend that the end consumer continues to use the oil “uninhibited,” however this will result in extra fast degradation of both the liquid and stable insulation.
It must be noted that some transformers already have a built-in oil preservation system; this is designed to keep dissolved oxygen at levels under 1000ppm. This can 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 isn’t required, although it might add further protection in opposition to oil oxidation if the preservation system ever fails. [2]
h) Passivator content material
PropertyCategoryGoodFairPoor
Passivator Content (mg/kg)O,A,B,C,D,E,F.>70 and steady, (rate of lower < 10/mg/kg/year)50-70mg/kg or<70mg/kg, with a significantrate of decrease of >10mg/kg/year<50 and lowering at >10mg/kg/year
Passivators, also called steel deactivators, react with reactive steel surfaces and dissolved metals similar to copper and silver and cut back their rate of reaction with compounds in the oil. This includes oxidation reactions with organic compounds and reactions with corrosive sulfur. Passivators are composed of two primary sorts, sulfur-based and nitrogen-based. The first instructed use of passivators in transformer oil, of which the writer 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 may deplete extra quickly; this depletion may speed up when the oil is un-inhibited.
With GOOD outcomes, regular pattern intervals could be maintained.
With FAIR outcomes, keep common monitoring.
When POOR, it’s suggested to remove the oil or remove the source of corrosivity from the oil by way of special oil therapy.
I) Sediment and sludge
This just isn’t a routine test.
It is suggested 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 have to be less than zero.02% by mass to be negligible. If the outcomes return a worth of more than 0.02% by mass, it is suggested that it be reclaimed; in any other case, an oil change is really helpful.
j) Interfacial pressure
This just isn’t 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 during the aging course of. What this means in sensible terms is there’s extra polar compound current in the oil, decreasing the power of an oil to serve as an insulator within the transformer system. There is a direct correlation between interfacial pressure and neutralisation quantity. Therefore, the interfacial pressure becomes a high quality criterion: the oil have to be modified beneath a predefined limit.
If outcomes are GOOD, continue the regular 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 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 may be vital. The extent of the corrosion damage brought on by the sulfur may be so extreme that it might cause failure of the tools if not checked. The addition of a copper passivator can reduce the influence of this compound on the transformer system.
In a examine by Doble, it has been discovered 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 would possibly contaminate the oil with corrosive sulfur.
CIGRE Brochure no 378, 2009 stipulates the necessity of corrective actions primarily based on this institute’s risk evaluation research. [4]
l) Particle counting and sizing
Table 3: Particles
Table B.1 – Typical contamination ranges (particles) encountered on power transformer insulating oil as measured using IEC 60970 [5]
m) Flashpoint ° C
Not a routine check
If there’s a maximum lower in flashpoints by 10%, the equipment might require further inspection. This worth would possibly differ in numerous countries.
It is advised to carry out this test when an unusual odour is noticed, the unit has been refilled, or an inner fault has occurred.
n) PCB (Polychlorinated Biphenyls)
This test is to not determine the condition of the transformer; this is a health and safety influence test. PCB is hazardous to each humans and the environment; it’s critical to test for PCBs after the retro fill of a transformer. It is also required whenever any maintenance has been done on the unit, and the potential for contamination is present. If PCB content material exceeds the recommended limits, the appropriate action needs to be taken.
Units with a PCB content material of greater than 50ppm require a fireplace safety 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 secure disposal issued to the tools proprietor.
Local regulatory our bodies outline the limits.
o) DGA (Dissolved Gas Analysis)
As DGA is an intricate science with lots of data and interpretation, we’ll talk about this phenomenon partly II of the article. The limits for the different gases and the interpretation of this data based on worldwide requirements might be discussed in detail, forming a part of the overall well being ranking determination of the transformer.
Conclusion
Transformer situation monitoring is an interlaced, extremely exciting field of research. In this text, we centered on the kinds of checks 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 particular unit at a specific date and time. This makes it attainable to make sure finest apply application and optimised maintenance. It additionally make it simpler to draw up a upkeep plan and motion plan.
References:
1. IEC 60422 Edition four.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.
4. 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 advisor. She has 20+ years’ experience in the trade, having beforehand labored as laboratory manager for a significant industrial laboratory group, specializing in transformer well being. She has been intrigued by transformer chemistry right from the start of her profession, notably within the analysis of take a look at knowledge. Corné has vast sensible and theoretical knowledge of reliability upkeep programmes.
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