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 collecting, measuring, recording, and evaluation of the relevant data concerning an asset’s operation. If we interpret the info correctly, it can provide us nice insight into the asset’s situation.
Frequent monitoring of the asset can lead to much less upkeep required or more prolonged periods without any upkeep required.
It is essential to identify the important thing parameters that are wanted to provide us an entire picture of the actual status of the transformer and the action we need to take to ensure the continued reliability of the asset to attain the utmost lifetime.
What is the information telling us?
Has the condition of the unit modified because the last maintenance period?
Is เกจวัดแก๊ส secure to function the unit?
Are there signs of deterioration?
Is it protected to load the unit above the nameplate score for a particular period?
Are we required to implement action to make sure the continued reliability of the unit?
How long can we use the unit earlier than we want to contemplate replacement?
Are the recognized problems of a recurring nature?
Effective condition monitoring define
It is vitally important to establish clear targets as part of your technique. What do you want to achieve by implementing this condition monitoring plan? Is it in-service failure prevention? Or perhaps life extension? Maintenance deferral? By stipulating the outcome and what you wish to accomplish, it might be a lot easier to determine the required parameters.
Health indexing of belongings is changing into a outstanding tool in getting a clearer image of the condition of your transformer. Test parameters carry a numerical value-adding to the total value of the Health Index Value of the transformer. These parameter weight values have been calculated primarily based on the worldwide standards for mineral oils, indicating the critical values stipulated within the numerous requirements.
The scope of oil evaluation, interpretation of the information, and significant values
At the beginning of this section, it’s important to state that we take care of completely different size transformers in the industry. Transformers are divided into lessons according to the kV scores of the tools. It is up to the reliability or asset supervisor to use the guidelines for larger gear, thereby implementing shorter increment oil analysis and electrical exams.
The maintenance engineer or supervisor needs to determine what kind of testing would benefit him in figuring out drawback areas within his fleet. Some of the evaluation has been identified as to routine type checks. Still, there could be an extensive vary of checks that can assist in identifying specific drawback standards within the system, which might not be clear via the standard day-to-day analysis often performed.
Please see the ranking lessons in TABLE 1
TABLE 1 FIG
TABLE 2 explains which oil analyses are beneficial and the way often or beneath which circumstances.
TABLE 2 FIG
Oil sampling
The taking of the oil sample is one of the most important and significant influencers in the evaluation outcome. If a pattern just isn’t taken to the prescribed procedure, then there is a vital possibility that the analysis carried out, and the results acquired, are of no use.
Care ought to be taken to make sure high quality management procedures are utilized in every step of the sampling course of as set out by international standards. A good quality sample taken by applying the right process is important. A sample could be contaminated by numerous elements, all of which might influence the result of the results in a negative method.
All steps concerned in sample taking must adhere to quality control procedures, together with the container that is used, the sampling kit, the taking of the pattern, the marking of the pattern, the closing of the pattern, the storage and dealing with of the sample, and then the supply of the sample to the laboratory.
If the pattern identification and sample knowledge are handwritten, the human issue can lead to incorrect interpretation of the information. The label ought to be stuck onto the container to make sure no mix-ups in sample 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 should be oil- and water resistant. Otherwise, some data may be lost, making it extraordinarily troublesome for the laboratory personnel to finish the report or allocate the sample to a selected transformer.
Now, let’s focus on the kinds of checks to determine the transformer’s condition, the crucial 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 sample arrives on the laboratory, one of the “tests” is a visual inspection of the oil sample in a transparent vessel to discover out the color, turbidity, and attainable particle identification.
Dark oils would possibly point out chemical degradation or contamination of the oil.
When there might be a lot of turbidity, it would point out a high water content material in the oil.
If the drain valve was not cleaned by the sampler, the filth particles in the drain valve could be included into the sample. If particles are recognized as carbon, it’d point out a attainable electrical fault in the unit. The DGA analysis of the oil will affirm if that’s so.
Clear oils with out contamination will indicate an excellent condition, and no action is recommended.
When oils are dark or turbid, further analysis will confirm any problems. The oil evaluation outcomes may also decide the diploma and sort 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 software
G <30
This is a routine inspection.
Breakdown voltage will indicate 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 within the unit, the breakdown voltage should be high.
If the values are Good, it is recommended to proceed with the present sample interval action plan.
If the values are Fair, more frequent sampling is beneficial in collaboration with different 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 alternative exams point out severe getting older, the oil may be changed with new or reclaimed oil. Another option can be to perform 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 removed from the oil. This course of removes acid and water in addition to some other compounds. Another benefit is that the oil can be re-used, and in most conditions, this may be carried out with out switching off the unit, which contributes to cost-saving. If doubtful – as a substitute swap off the unit throughout this therapy course of.
If the values are Poor, it is advisable to take motion as quickly as possible and not delay the upkeep course of. Excess water within the transformer system decreases the projected transformer lifetime significantly; extraordinarily excessive water content material could cause flashover in the unit, resulting in 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 take a look at
This is a routine take a look at for all courses of electrical tools, besides class G
The outcomes of this take a look at should always be thought of in conjunction with the breakdown energy. If it’s discovered that the water content is high and the breakdown strength is low, additional action must be taken. It is recommended that a second pattern from the same unit is examined to substantiate the results.
In the case of switching equipment, where there is no paper present, the breakdown voltage is the determining issue.
It must be noted that the bounds indicated by IEC 60422 Edition 4 apply to transformers with working temperatures between forty and 70 °C. If it is discovered that the unit’s operating temperature is exterior this temperature vary, it’s best to check with Annex A of the standard.
When the worth obtained through analyses is GOOD, the traditional sampling interval may be maintained, requiring no additional action.
When the value returns a FAIR result, more frequent sampling is beneficial. It can be useful to suppose about other parameters like the breakdown voltage, particle content and DDF/resistivity, and acidity to determine on the action to be applied.
A POOR outcome will require instant action from the asset manager. This may embrace taking another sample to confirm the outcomes from the first evaluation. If it is confirmed that the water content is high, the oil can be filtered; this process should remove a large portion of the moisture from the oil if applied correctly. Follow-up samples have to be taken to guarantee that the moisture content material remains to be within the required limits. The purpose is that the most significant portion of the water is caught up in the paper system in the transformer. This moisture will move from the paper into the oil beneath situations that favour this movement. It may be discovered later that the oil within the water has increased again with none obvious reason, but the supply could be the paper in the transformer.
A visible inspection can also be beneficial to determine if any water might transfer into the transformer or electrical gear by way of leaks. This downside might be extra 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.a hundred.10 to zero.15>0.15
B, E<0.one hundred.10 to 0.25>0.20
C<0.one hundred.15 to 0.30>0.30
F, G Not a routine test
This is a routine check for all courses besides F and G
The acids in oils are shaped as a result of chemical reactions between the oil, water, and paper. Higher temperatures 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 will enhance paper degradation. If left untreated in transformers, this could lead to sludge formation, normally around the decrease elements of the transformer core. The sludge will ultimately kind a semi-solid substance that’s extraordinarily difficult to remove.
If the result’s GOOD, the regular sampling interval can proceed.
In case of a FAIR outcome, the sampling interval must be decreased to fit the state of affairs. Future analysis should include a visual inspection of the oil for sediment and sludge.
If the result is POOR based on the prescribed values in IEC 60422 Edition 4.0, the asset supervisor may decide to reclaim the oil or exchange it with new or reclaimed oil, whichever option might swimsuit their necessities 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.a hundred.10 to 0.20>0.20
B, C<0.100.10 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 check for all courses of electrical equipment, besides F and G
The dielectric dissipation issue or tan delta of this test provides data concerning 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 phase displacement and dielectric losses. Other impurities that may influence the dissipation issue embrace water, dissolved insulating resin, and paper.
When the result’s FAIR, more frequent sampling and checking additional parameters is beneficial.
When the result is POOR, reclamation or an oil change is really helpful. The structure of the oil is damaged, 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 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 take a look at
DC resistivity of the oil is considered one of the key parameters to assess the transformer insulation condition; this is based on the fact that DC resistance is delicate to oil degradation.
When the result is FAIR, extra frequent sampling and checking further 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 unique worth
This take a look at is restricted to oils with this additive.
It could be advisable to contact the oil supplier to confirm the small print regarding components.
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 function of the inhibitor is to stop oxygen from reacting with the oil. This significantly slows the getting older process in the oil and the strong insulation.
If the result is FAIR, it is advised to top up the inhibitor degree to the prescribed stage per supplier instructions. It is suggested to make use of a subject skilled educated in the procedure to perform this task.
If the result obtained is POOR, the recommendation for this scenario would counsel that the end consumer continues to make use of the oil “uninhibited,” but this will lead to more speedy degradation of each the liquid and strong 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 levels beneath 1000ppm. This can 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 beneath these circumstances is not 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 secure, (rate of lower < 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 called steel deactivators, react with reactive metallic surfaces and dissolved metals such as copper and silver and scale back their fee of response with compounds in the oil. This includes oxidation reactions with natural compounds and reactions with corrosive sulfur. Passivators are composed of two fundamental sorts, sulfur-based and nitrogen-based. The first advised 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 might accelerate when the oil is un-inhibited.
With GOOD outcomes, regular pattern intervals may be maintained.
With FAIR outcomes, maintain common monitoring.
When POOR, it’s advised to remove the oil or take away the supply of corrosivity from the oil by way of special oil remedy.
I) Sediment and sludge
This just isn’t a routine take a look at.
It is advised that this take a look at is carried out when the oil results point out a high acid worth and the dissipation factor is near the unacceptable limit.
The outcomes have to be lower than zero.02% by mass to be negligible. If the results return a value of greater than zero.02% by mass, it is instructed that it be reclaimed; otherwise, 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 check
F, GNot Applicable
The interfacial pressure between transformer oil and water reduces in the course of the growing older course of. What this means in sensible phrases is there is more polar compound present within the oil, decreasing the flexibility of an oil to function an insulator within the transformer system. There is a direct correlation between interfacial pressure and neutralisation number. Therefore, the interfacial pressure becomes a high quality criterion: the oil have to be changed beneath a predefined limit.
If results are GOOD, proceed the common sampling interval.
If outcomes are FAIR, lower the sampling interval.
If outcomes are POOR, verify 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 effect on the transformer system can be vital. The extent of the corrosion injury attributable to the sulfur could be so extreme that it might trigger failure of the equipment if not checked. The addition of a copper passivator can reduce the impact of this compound on the transformer system.
In ตัววัดแรงดันน้ำ by Doble, it has been found that rubber products utilized in transformers would possibly add to the corrosivity of the oil. Nitrile rubber gaskets and hoses not accredited for oil filtration might contaminate the oil with corrosive sulfur.
CIGRE Brochure no 378, 2009 stipulates the need of corrective actions based mostly on this institute’s danger evaluation research. [4]
l) Particle counting and sizing
Table 3: Particles
Table B.1 – Typical contamination levels (particles) encountered on power transformer insulating oil as measured utilizing IEC 60970 [5]
m) Flashpoint ° C
Not a routine test
If there is a most decrease in flashpoints by 10%, the tools may require further inspection. This worth would possibly differ in different countries.
It is advised to perform this take a look at when an uncommon odour is noticed, the unit has been refilled, or an internal fault has occurred.
n) PCB (Polychlorinated Biphenyls)
This test is to not decide the condition of the transformer; it is a health and security impact check. PCB is hazardous to each humans and the surroundings; it is important to test 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 chance of contamination is current. If PCB content exceeds the really helpful limits, the suitable action needs to be taken.
Units with a PCB content of greater than 50ppm require a hearth safety plan, environmental safety plan, and further precautionary measures when upkeep is finished. This oil needs to be changed, and the oil disposed of as hazardous waste, with a certificate of safe disposal issued to the gear proprietor.
Local regulatory bodies outline the boundaries.
o) DGA (Dissolved Gas Analysis)
As DGA is an intricate science with a lot of knowledge and interpretation, we’ll focus on this phenomenon partially II of the article. The limits for the completely different gases and the interpretation of this knowledge according to international requirements might be mentioned in detail, forming part of the general health score willpower of the transformer.
Conclusion
Transformer situation monitoring is an interlaced, extremely exciting subject of study. In this text, we centered on the types of checks to determine the condition of the transformer, the important values, and the recommended actions.
The Health Index indication makes it attainable to see the supposed reliability of a selected unit at a specific date and time. This makes it attainable to make sure best practice application and optimised maintenance. It also make it easier to draw up a maintenance plan and action plan.
References:
1. IEC 60422 Edition four.0 2013-01 International Standard (Mineral insulating oils in electrical gear – supervision and upkeep guide)
2. Oxidation inhibitor and reinhabiting oil-filled transformers, by Andy Shkolnik
3. Passivators, what they’re and how 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 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 marketing consultant. She has 20+ years’ experience in the trade, having previously 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, significantly in the analysis of take a look at knowledge. Corné has huge sensible and theoretical information of reliability upkeep programmes.
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