เนื้อแดดเดียว จัดส่งทั่วประเทศ

065-629-6350

PETROL CHEMICALS

TALKING TRANSFORMER TESTING

by Brenna ShumbamhiniJune 9, 2022

Share

Introduction

Corne Dames

Condition monitoring is the frequent accumulating, measuring, recording, and analysis of the related data concerning an asset’s operation. If we interpret the information appropriately, it may give us nice perception into the asset’s situation.
Frequent monitoring of the asset can result in much less maintenance required or extra prolonged intervals without any maintenance required.
It is essential to establish the necessary thing parameters which may be wanted to give us a whole image of the particular status of the transformer and the motion we have to take to ensure the continued reliability of the asset to achieve the maximum lifetime.
What is the data telling us?

Has the condition of the unit modified since the last upkeep period?

Is it secure to function the unit?

Are there indicators of deterioration?

Is it secure to load the unit above the nameplate score 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 recognized problems of a recurring nature?

Effective situation monitoring outline

It is vitally essential to determine clear objectives as a half of your strategy. What do you need to achieve by implementing this condition monitoring plan? Is it in-service failure prevention? Or maybe life extension? Maintenance deferral? By stipulating the outcome and what you need to accomplish, it might be a lot simpler to determine the required parameters.
Health indexing of belongings is becoming a outstanding tool in getting a clearer image of the situation 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 were calculated based mostly on the international requirements for mineral oils, indicating the critical values stipulated in the numerous standards.
The scope of oil analysis, interpretation of the information, and important values

At the beginning of this section, it’s essential to state that we cope with totally different size transformers within the business. Transformers are divided into classes in accordance with the kV scores of the tools. It is as much as the reliability or asset supervisor to use the guidelines for larger equipment, thereby implementing shorter increment oil evaluation and electrical checks.
The maintenance engineer or supervisor needs to determine what kind of testing would profit him in figuring out downside areas within his fleet. Some of the evaluation has been identified as to routine sort exams. Still, there is an extensive range of checks that can help in identifying specific problem standards throughout the system, which could not be clear via the typical day-to-day analysis usually carried out.
Please see the ranking 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 pattern is likely one of the most vital and important influencers within the analysis outcome. If a sample is not taken to the prescribed procedure, then there is a important possibility that the evaluation carried out, and the outcomes acquired, are of no use.
Care ought to be taken to make sure high quality management procedures are applied in each step of the sampling process as set out by worldwide requirements. A good high quality sample taken by making use of the proper procedure is crucial. A pattern could be contaminated by numerous factors, all of which can affect the outcome of the ends in a unfavorable method.
All steps concerned in sample taking should adhere to quality management procedures, including the container that is used, the sampling package, the taking of the sample, the marking of the pattern, the closing of the pattern, the storage and dealing with of the pattern, after which the delivery of the pattern to the laboratory.
If the sample identification and pattern information are handwritten, the human factor can lead to incorrect interpretation of the info. The label must 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 should be waterproof, and the pen used to put in writing on the label must be oil- and water-resistant. Otherwise, some knowledge may be misplaced, making it extremely difficult for the laboratory personnel to complete the report or allocate the sample to a selected transformer.
Now, let’s discuss the types of checks to determine the transformer’s situation, the important values, and the really helpful actions in each case:
a) Colour and look

This is a routine inspection utilized to every oil pattern.
When an oil sample arrives at the laboratory, one of many “tests” is a visible inspection of the oil pattern in a clear vessel to find out the color, turbidity, and potential particle identification.
Dark oils may indicate chemical degradation or contamination of the oil.
When there could be a lot of turbidity, it would point out a excessive water content material in the oil.
If the drain valve was not cleaned by the sampler, the dust particles within the drain valve might be integrated into the pattern. If particles are recognized as carbon, it might point out a possible electrical fault within the unit. The DGA analysis of the oil will verify if that’s so.
Clear oils with out contamination will point out a great condition, and no action is really helpful.
When oils are darkish or turbid, further analysis will verify any problems. The oil evaluation results may even determine the degree 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 point application<40 kV for OLTC in delta or line-end application G <30 This is a routine inspection.
Breakdown voltage will indicate 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 keep away from flashover in the unit, the breakdown voltage have to be high.
If the values are Good, it is strongly recommended to continue with the present pattern interval action plan.
If the values are Fair, extra frequent sampling is recommended in collaboration with different parameter results like the water content, DDF (dielectric dissipation factor), and acidity.
If values are Poor – it is strongly recommended to recondition the oil via oil reconditioning processes. If various checks indicate extreme getting older, the oil may be changed with new or reclaimed oil. Another choice could 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 elements are faraway from the oil. This process removes acid and water as nicely as another compounds. Another advantage is that the oil may be re-used, and in most conditions, this might be carried out with out switching off the unit, which contributes to cost-saving. If in doubt – as a substitute swap off the unit throughout this therapy course of.
If the values are Poor, it’s advisable to take motion as quickly as attainable and never delay the maintenance process. Excess water within the transformer system decreases the projected transformer lifetime considerably; extremely high water content can cause flashover in the unit, resulting in loss 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 classes of electrical tools, besides class G

The results of this check should always be considered along side the breakdown strength. If it is found that the water content material is high and the breakdown energy is low, additional motion needs to be taken. It is beneficial that a second pattern from the same unit is examined to substantiate the results.
In the case of switching tools, the place there is not a paper present, the breakdown voltage is the figuring out factor.
It should be famous that the bounds indicated by IEC 60422 Edition 4 apply to transformers with working temperatures between forty and 70 °C. If it is found that the unit’s operating temperature is outside this temperature vary, it is best to refer to Annex A of the usual.
When เกจวัดแรงดันลมดิจิตอล obtained by way of analyses is GOOD, the traditional sampling interval may be maintained, requiring no additional action.
When the value returns a FAIR result, extra frequent sampling is beneficial. It can also be helpful to contemplate other parameters like the breakdown voltage, particle content and DDF/resistivity, and acidity to decide on the motion to be implemented.
A POOR end result will require quick motion from the asset supervisor. This might embrace taking another sample to confirm the results from the first analysis. If it is confirmed that the water content is excessive, the oil can be filtered; this process should take away a big portion of the moisture from the oil if utilized accurately. Follow-up samples need to be taken to ensure that the moisture content material is still inside the required limits. The purpose is that probably the most good portion of the water is caught up in the paper system within the transformer. This moisture will move from the paper into the oil underneath situations that favour this motion. It could be discovered later that the oil within the water has increased once more without any apparent purpose, however the supply could be the paper in the transformer.
A visible inspection is also recommended to determine if any water would possibly move into the transformer or electrical equipment by way of leaks. This downside may be extra severe if the transformer or electrical tools is outside and not in a coated area.
d) Acidity (mgKOH/g oil) Neutralization Number

PropertyCategoryGoodFairPoor

Acidity mgKOH/g oilO, A, D<0.a hundred.10 to 0.15>0.15

B, E<0.100.10 to 0.25>0.20

C<0.one hundred.15 to zero.30>0.30

F, G Not a routine test

This is a routine take a look at for all classes besides F and G

The acids in oils are fashioned because of chemical reactions between the oil, water, and paper. Higher temperatures or load increases will help in the formation of the acids. Because acids are polar compounds, it will 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 form a semi-solid substance that’s extremely troublesome to take away.
If the result’s GOOD, the regular sampling interval can continue.
In case of a FAIR result, the sampling interval ought to be decreased to suit the situation. Future evaluation ought to embrace a visible inspection of the oil for sediment and sludge.
If the result’s POOR based on the prescribed values in IEC 60422 Edition four.0, the asset manager 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.one 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.a hundred.01 to 0.30>0.03

F, GNot a routine take a look at

This is a routine test for all lessons of electrical equipment, besides F and G

The dielectric dissipation factor or tan delta of this check supplies data concerning 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, leading to section displacement and dielectric losses. Other impurities that might influence the dissipation issue include water, dissolved insulating resin, and paper.
When the result is FAIR, extra frequent sampling and checking further parameters is recommended.
When the result is POOR, reclamation or an oil change is beneficial. The structure of the oil is broken, in effect that the chemical bonds between the molecules have damaged down, and even with filtration, the really helpful 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 test DC resistivity of the oil is certainly one of the key parameters to assess the transformer insulation condition; that is based mostly on the fact that DC resistance is sensitive to oil degradation.
When the result is FAIR, extra frequent sampling and checking further parameters is beneficial.
When the result is 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 original value<40% of unique value This test is restricted to oils with this additive.
It would be advisable to contact the oil supplier to verify the small print concerning components.
The two commonest oxidation inhibitors for transformer oils are 2,6-di-tertiary-butyl para-cresol (DBPC) and a couple of,6-di-tertiary butyl-phenol (DBP). The purpose of the inhibitor is to forestall oxygen from reacting with the oil. This significantly slows the aging process in the oil and the solid insulation.
If the result’s FAIR, it is suggested to prime up the inhibitor stage to the prescribed degree per supplier instructions. It is advised to use a area professional trained in the procedure to perform this activity.
If the end result obtained is POOR, the recommendation for this state of affairs would suggest that the end person continues to make use of the oil “uninhibited,” but this will likely lead to extra fast degradation of both the liquid and stable insulation.
It should be noted that some transformers already have a built-in oil preservation system; this is designed to maintain dissolved oxygen at levels under 1000ppm. This could 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 beneath these circumstances is not required, though it would add additional safety against 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 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 referred to as steel deactivators, react with reactive metallic surfaces and dissolved metals similar to copper and silver and reduce their rate of response with compounds in the oil. This contains oxidation reactions with natural compounds and reactions with corrosive sulfur. Passivators are composed of two fundamental types, sulfur-based and nitrogen-based. The first instructed use of passivators in transformer oil, of which the writer 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 rapidly; this depletion would possibly speed up when the oil is un-inhibited.
With GOOD outcomes, common pattern intervals can be maintained.
With FAIR outcomes, maintain common monitoring.
When POOR, it’s suggested to remove the oil or remove the supply of corrosivity from the oil via special oil treatment.
I) Sediment and sludge

This isn’t a routine take a look at.
It is suggested that this test is carried out when the oil outcomes indicate a high acid value and the dissipation issue is near the unacceptable limit.
The results need to be lower than 0.02% by mass to be negligible. If the results return a value of greater than zero.02% by mass, it’s instructed that or not it’s reclaimed; otherwise, an oil change is recommended.
j) Interfacial pressure

This 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 test F, GNot Applicable The interfacial tension between transformer oil and water reduces in the course of the aging course of. What this implies in sensible terms is there is more polar compound present within the oil, lowering the ability of an oil to function an insulator within the transformer system. There is a direct correlation between interfacial pressure and neutralisation quantity. Therefore, the interfacial tension becomes a excessive quality criterion: the oil must be changed under a predefined limit.
If outcomes are GOOD, proceed the regular sampling interval.
If results are FAIR, decrease 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 either 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 brought on by the sulfur may be so severe that it might 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 discovered that rubber merchandise used in transformers may add to the corrosivity of the oil. Nitrile rubber gaskets and hoses not permitted for oil filtration might contaminate the oil with corrosive sulfur.
CIGRE Brochure no 378, 2009 stipulates the necessity of corrective actions primarily based on this institute’s threat evaluation research. [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 check

If there’s a maximum decrease in flashpoints by 10%, the tools may require further inspection. This worth would possibly differ in numerous countries.
It is advised to perform this check when an uncommon odour is noticed, the unit has been refilled, or an inside fault has occurred.
n) PCB (Polychlorinated Biphenyls)

This check is not to decide the situation of the transformer; this could be a health and safety impression test. PCB is hazardous to each humans and the environment; it is vital to check for PCBs after the retro fill of a transformer. It can also be required each time any upkeep has been carried out on the unit, and the possibility of contamination is current. If PCB content material exceeds the recommended limits, the suitable motion needs to be taken.
Units with a PCB content material of greater than 50ppm require a fire security plan, environmental safety plan, and additional precautionary measures when maintenance is finished. This oil needs to be replaced, and the oil disposed of as hazardous waste, with a certificate of protected disposal issued to the tools proprietor.
Local regulatory bodies outline the limits.
o) DGA (Dissolved Gas Analysis)

As DGA is an intricate science with a lot of knowledge 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 data in accordance with international requirements will be discussed in detail, forming a part of the overall health score determination of the transformer.
Conclusion

Transformer situation monitoring is an interlaced, highly exciting area of examine. In this article, we targeted on the kinds of tests to determine the condition of the transformer, the crucial values, and the really helpful actions.
The Health Index indication makes it attainable to see the supposed reliability of a selected unit at a selected date and time. This makes it possible to ensure best follow software and optimised maintenance. It additionally make it simpler to draw up a upkeep plan and motion plan.
References:
1. IEC 60422 Edition four.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 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 revealed by Transformer Technology Magazine Issue 16 – 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 beforehand labored as laboratory supervisor for a serious industrial laboratory group, focusing on transformer well being. She has been intrigued by transformer chemistry proper from the start of her profession, significantly in the analysis of take a look at information. Corné has huge practical and theoretical knowledge of reliability maintenance programmes.
Share

Leave a Reply

Your email address will not be published. Required fields are marked *