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 related data relating to an asset’s operation. If we interpret the information accurately, it can give us nice perception into the asset’s situation.
Frequent monitoring of the asset may end up in much less upkeep required or extra extended durations with none maintenance required.
It is crucial to determine the key parameters that are wanted to provide us a complete image of the particular status of the transformer and the motion we need to take to ensure the continued reliability of the asset to attain the maximum lifetime.
What is the data telling us?
Has the condition of the unit changed for the explanation that final maintenance period?
Is it secure to operate the unit?
Are there indicators of deterioration?
Is it protected to load the unit above the nameplate ranking for a specific period?
Are we required to implement motion to ensure the continued reliability of the unit?
How long can we use the unit earlier than we want to consider replacement?
Are the recognized problems of a recurring nature?
เกจวัดแรงดันอากาศ monitoring define
It is vitally necessary to establish clear objectives as part of your strategy. What do you want to obtain by implementing this condition monitoring plan? Is it in-service failure prevention? Or possibly life extension? Maintenance deferral? By stipulating the end result and what you want to accomplish, it might be much easier to establish the required parameters.
Health indexing of property is changing into a exceptional software 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 were 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 part, it’s important to state that we deal with completely different measurement transformers in the trade. Transformers are divided into courses according to the kV scores of the gear. It is as a lot as the reliability or asset manager to make use of the guidelines for bigger tools, thereby implementing shorter increment oil evaluation and electrical checks.
The maintenance engineer or supervisor needs to discover out what kind of testing would benefit him in identifying drawback areas inside his fleet. Some of the analysis has been recognized as to routine kind exams. Still, there may be an extensive range of tests that can assist in figuring out specific drawback standards inside the system, which could not be clear via the everyday day-to-day analysis usually carried out.
Please see the score courses in TABLE 1
TABLE 1 FIG
TABLE 2 explains which oil analyses are recommended and the way usually or beneath which circumstances.
TABLE 2 FIG
Oil sampling
The taking of the oil pattern is amongst the most crucial and critical influencers in the evaluation consequence. If a pattern is not taken to the prescribed procedure, then there’s a important risk that the evaluation carried out, and the outcomes acquired, are of no use.
Care should be taken to ensure high quality control procedures are utilized in every 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 sample may be contaminated by various elements, all of which can affect the outcome of the leads to a unfavorable manner.
All steps concerned in pattern taking should adhere to high quality control procedures, together with 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 sample to the laboratory.
If the pattern identification and sample information are handwritten, the human issue can result in incorrect interpretation of the data. The label must be stuck onto the container to ensure no mix-ups in sample identification. Ensure that the label is accomplished in neat, easy-to-read handwriting. The label ought to be waterproof, and the pen used to write down on the label ought to be oil- and water resistant. Otherwise, some knowledge might be lost, making it extremely difficult for the laboratory personnel to complete the report or allocate the pattern to a particular transformer.
Now, let’s discuss the types of exams to discover out the transformer’s condition, the crucial values, and the really helpful actions in every case:
a) Colour and appearance
This is a routine inspection utilized to each oil sample.
When an oil pattern arrives on the laboratory, one of many “tests” is a visual inspection of the oil sample in a clear vessel to determine the colour, turbidity, and attainable particle identification.
Dark oils might indicate chemical degradation or contamination of the oil.
When there could be plenty of turbidity, it might point out a high water content material in the oil.
If the drain valve was not wiped clean by the sampler, the dust particles in the drain valve might 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 verify if that’s so.
Clear oils with out contamination will point out an excellent condition, and no motion is really helpful.
When oils are dark or turbid, further evaluation will confirm any problems. The oil evaluation results will also determine the degree and type 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 foreign particles, or both within the oil being analysed.
As the oil in transformers acts as an insulation medium to keep away from flashover within the unit, the breakdown voltage must be high.
If the values are Good, it is strongly recommended to continue with the present sample interval motion plan.
If the values are Fair, more frequent sampling is really helpful in collaboration with different parameter outcomes like the water content, DDF (dielectric dissipation factor), and acidity.
If values are Poor – it is strongly recommended to recondition the oil by way of oil reconditioning processes. If alternative tests indicate severe getting older, the oil may be replaced with new or reclaimed oil. Another option can be to carry out on-site oil reclamation using 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 in addition to some other compounds. Another benefit is that the oil could be re-used, and in most situations, this could be accomplished with out switching off the unit, which contributes to cost-saving. If unsure – as a substitute swap off the unit throughout this treatment process.
If the values are Poor, it is advisable to take motion as soon as potential and never delay the upkeep process. Excess water within the transformer system decreases the projected transformer lifetime significantly; extremely excessive water content material could cause flashover in the unit, resulting in loss of the asset.
c) Water content (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, except class G
The outcomes of this take a look at ought to at all times be thought of at the side of the breakdown strength. If it’s found that the water content is high and the breakdown power is low, further motion needs to be taken. It is recommended that a second pattern from the identical unit is tested to substantiate the results.
In the case of switching tools, the place there is not a paper current, the breakdown voltage is the figuring out factor.
It must be noted that the limits indicated by IEC 60422 Edition four apply to transformers with operating temperatures between 40 and 70 °C. If it’s found that the unit’s operating temperature is exterior this temperature vary, it is best to discuss with Annex A of the usual.
When the worth obtained through analyses is GOOD, the conventional sampling interval could be maintained, requiring no additional motion.
When the value returns a FAIR end result, more frequent sampling is really helpful. It is also helpful to contemplate different parameters just like the breakdown voltage, particle content and DDF/resistivity, and acidity to resolve on the motion to be applied.
A POOR end result will require instant action from the asset manager. This would possibly include taking one other pattern to confirm the outcomes from the primary evaluation. If it’s confirmed that the water content material is high, the oil may be filtered; this course of ought to 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 remains to be throughout the required limits. The cause is that probably 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 conditions that favour this movement. It might be found later that the oil in the water has increased again without any apparent purpose, however the source can be the paper in the transformer.
A visible inspection can also be really helpful to find out if any water would possibly transfer into the transformer or electrical tools via leaks. This drawback could be extra extreme if the transformer or electrical gear is exterior and not in a covered 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 take a look at
This is a routine check for all courses besides F and G
The acids in oils are shaped as a end result of chemical reactions between the oil, water, and paper. Higher temperatures or load will increase will help within the formation of the acids. Because acids are polar compounds, it will adversely have an effect on the insulation properties of the oil and will improve paper degradation. If left untreated in transformers, this can result in sludge formation, normally across the decrease components of the transformer core. The sludge will ultimately kind a semi-solid substance that is extraordinarily tough to remove.
If the result’s GOOD, the regular sampling interval can continue.
In case of a FAIR end result, the sampling interval should be decreased to fit the state of affairs. Future evaluation should include a visual inspection of the oil for sediment and sludge.
If the result’s POOR based on the prescribed values in IEC 60422 Edition 4.0, the asset manager may resolve to reclaim the oil or substitute it with new or reclaimed oil, whichever choice may 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.a hundred.10 to zero.20>0.20
B, C<0.one hundred.10 to 0.50>0.50
D<0.010.01 to 0.03>0.03
E<0.100.01 to 0.30>0.03
F, GNot a routine take a look at
This is a routine take a look at for all classes of electrical equipment, besides F and G
The dielectric dissipation issue or tan delta of this test supplies information relating to 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 that may affect the dissipation factor embrace water, dissolved insulating resin, and paper.
When the result’s FAIR, extra frequent sampling and checking further parameters is beneficial.
When the result’s POOR, reclamation or an oil change is really helpful. The structure 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 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 check
DC resistivity of the oil is considered 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’s FAIR, extra frequent sampling and checking further parameters is recommended.
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 original value<40% of unique worth
This test is restricted to oils with this additive.
It would be advisable to contact the oil supplier to confirm the small print concerning 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 purpose of the inhibitor is to stop oxygen from reacting with the oil. This considerably slows the getting older course of in the oil and the solid insulation.
If the result is FAIR, it’s suggested to prime up the inhibitor level to the prescribed degree per supplier instructions. It is suggested to make use of a field skilled educated in the procedure to carry out this task.
If the end result obtained is POOR, the advice for this scenario would suggest that the end consumer continues to use the oil “uninhibited,” however this will result in more fast degradation of each the liquid and solid insulation.
It must be famous that some transformers have already got a built-in oil preservation system; that 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 outfitted with a rubber diaphragm (bladder). Using inhibited oils beneath these circumstances just isn’t required, though it might add additional safety towards 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 decrease < 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 known as metal deactivators, react with reactive metal surfaces and dissolved metals such as copper and silver and reduce their rate of response with compounds within the oil. This consists of oxidation reactions with organic compounds and reactions with corrosive sulfur. Passivators are composed of two fundamental varieties, sulfur-based and nitrogen-based. The first suggested 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 extra 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 regular 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 is not a routine test.
It is advised that this take a look at is carried out when the oil results indicate a high acid worth and the dissipation issue is close to the unacceptable restrict.
The results must be less than zero.02% by mass to be negligible. If the results return a worth of more than 0.02% by mass, it’s instructed that it’s reclaimed; otherwise, an oil change is beneficial.
j) Interfacial rigidity
This just isn’t a routine take a look at
PropertyCategoryGoodFairPoor
Interfacial Tension (mN/m)O, A, B, C, DInhibited Uninhibited>28 >2522 to twenty-eight 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 getting older course of. What this means in sensible phrases is there is more polar compound current in the oil, reducing the power 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 tension becomes a quality criterion: the oil have to be changed below a predefined limit.
If results are GOOD, proceed the common 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 is not a routine take a look at.
Oil is either corrosive or non-corrosive.
The presence of corrosive sulfur in transformer oil and its effect on the transformer system may be vital. The extent of the corrosion harm brought on by the sulfur can be so extreme that it’d 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 a examine by Doble, it has been discovered that rubber products used in transformers would possibly 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 need of corrective actions based on this institute’s danger assessment study. [4]
l) Particle counting and sizing
Table 3: Particles
Table B.1 – Typical contamination ranges (particles) encountered on energy transformer insulating oil as measured utilizing IEC 60970 [5]
m) Flashpoint ° C
Not a routine check
If there’s a most lower in flashpoints by 10%, the tools would possibly require additional inspection. This value would possibly differ in different countries.
It is advised to carry out this take a look at when an unusual odour is observed, the unit has been refilled, or an inside fault has occurred.
n) PCB (Polychlorinated Biphenyls)
This take a look at is to not determine the situation of the transformer; this is a health and security impact test. PCB is hazardous to both humans and the setting; it is important to check for PCBs after the retro fill of a transformer. It is also required each time any upkeep has been done on the unit, and the potential of contamination is present. If PCB content exceeds the beneficial limits, the suitable motion needs to be taken.
Units with a PCB content of greater than 50ppm require a hearth security plan, environmental safety plan, and additional precautionary measures when upkeep is finished. This oil must be changed, and the oil disposed of as hazardous waste, with a certificates of secure disposal issued to the tools owner.
Local regulatory bodies define the limits.
o) DGA (Dissolved Gas Analysis)
As DGA is an intricate science with plenty of data and interpretation, we’ll focus on this phenomenon in part II of the article. The limits for the different gases and the interpretation of this data in accordance with international standards will be mentioned intimately, forming part of the overall health ranking dedication of the transformer.
Conclusion
Transformer situation monitoring is an interlaced, extremely exciting subject of research. In this text, we centered on the types 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 selected unit at a selected date and time. This makes it attainable to make sure greatest apply utility and optimised maintenance. It also make it simpler to draw up a maintenance plan and action plan.
References:
1. IEC 60422 Edition four.zero 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
three. Passivators, what they are and how 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 power.”
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 advisor. She has 20+ years’ experience in the business, having beforehand labored as laboratory manager for a serious industrial laboratory group, specializing in transformer health. She has been intrigued by transformer chemistry proper from the start of her profession, particularly in the evaluation of take a look at information. Corné has vast practical and theoretical knowledge of reliability upkeep programmes.
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