TALKING TRANSFORMER TESTING

PETROL CHEMICALS
TALKING TRANSFORMER TESTING
by Brenna ShumbamhiniJune 9, 2022
Share
Introduction
Corne Dames
Condition monitoring is the frequent accumulating, measuring, recording, and evaluation of the relevant data relating to an asset’s operation. If we interpret the data appropriately, it can provide us great insight into the asset’s condition.
Frequent monitoring of the asset can lead to less upkeep required or extra prolonged periods without any upkeep required.
It is crucial to establish the key parameters which are wanted to give us an entire picture of the actual standing 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 situation of the unit modified because the final upkeep period?
Is it protected to function the unit?
Are there indicators of deterioration?
Is it secure to load the unit above the nameplate score for a selected period?
Are we required to implement action to ensure the continued reliability of the unit?
How long can we use the unit before we want to consider replacement?
Are the identified problems of a recurring nature?
Effective situation monitoring define
It is vitally essential to establish clear goals as a part of your strategy. What do you need to obtain by implementing this situation monitoring plan? Is it in-service failure prevention? Or perhaps เกจวัดแรงอัดกระบอกสูบ ? Maintenance deferral? By stipulating the finish result and what you need to accomplish, it would be much easier to determine the required parameters.
Health indexing of property is changing into a outstanding tool in getting a clearer picture of the situation of your transformer. Test parameters carry a numerical value-adding to the total worth of the Health Index Value of the transformer. These parameter weight values were calculated based on the worldwide standards for mineral oils, indicating the critical values stipulated in the varied standards.
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 totally different measurement transformers in the industry. Transformers are divided into lessons according to the kV ratings of the tools. It is as much as the reliability or asset manager to make use of the guidelines for bigger gear, thereby implementing shorter increment oil evaluation and electrical exams.
The upkeep engineer or supervisor wants to determine what type of testing would benefit him in figuring out drawback areas within his fleet. Some of the evaluation has been identified as to routine type exams. Still, there might be an extensive vary of tests that can assist in identifying particular problem criteria inside the system, which might not be clear by way of the standard day-to-day evaluation usually performed.
Please see the ranking classes in TABLE 1
TABLE 1 FIG
TABLE 2 explains which oil analyses are really helpful and the way often or underneath which circumstances.
TABLE 2 FIG
Oil sampling
The taking of the oil sample is one of the most crucial and important influencers in the analysis end result. If a sample just isn’t taken to the prescribed process, then there is a significant possibility that the analysis carried out, and the results acquired, are of no use.
Care ought to be taken to make sure high quality control procedures are utilized in each step of the sampling process as set out by international standards. A good high quality sample taken by making use of the correct process is important. A pattern can be contaminated by varied factors, all of which may affect the finish result of the leads to a unfavorable manner.
All steps involved in sample taking should adhere to high quality control procedures, including the container that is used, the sampling equipment, the taking of the sample, the marking of the sample, the closing of the sample, the storage and handling of the sample, after which the supply of the pattern to the laboratory.
If the pattern identification and sample information are handwritten, the human factor 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 ought to be waterproof, and the pen used to put in writing on the label ought to be oil- and water resistant. Otherwise, some knowledge may be lost, making it extremely troublesome for the laboratory personnel to finish the report or allocate the pattern to a selected transformer.
Now, let’s discuss the forms of exams to determine the transformer’s situation, the crucial values, and the beneficial actions in every case:
a) Colour and appearance
This is a routine inspection applied to every oil pattern.
When an oil sample arrives at the laboratory, one of the “tests” is a visual inspection of the oil sample in a clear 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 เพรสเชอร์เกจลม of turbidity, it might indicate a excessive water content material within the oil.
If the drain valve was not wiped clean by the sampler, the filth particles within the drain valve could be integrated into the pattern. If particles are identified as carbon, it would indicate a potential electrical fault in the unit. The DGA evaluation of the oil will verify if this is the case.
Clear oils with out contamination will point out a good situation, and no motion is recommended.
When oils are darkish or turbid, additional evaluation will affirm any issues. The oil evaluation outcomes may even 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 point application<40 kV for OLTC in delta or line-end utility
G <30
This is a routine inspection.
Breakdown voltage will indicate the water content or the presence of overseas 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 must be excessive.
If the values are Good, it is strongly recommended to proceed with the current pattern interval motion plan.
If the values are Fair, extra frequent sampling is beneficial in collaboration with different parameter outcomes 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 checks indicate severe getting older, the oil can be changed with new or reclaimed oil. Another option can be to perform on-site oil reclamation using a reclamation plant.
Reclamation of oil has the advantage that the color of the oil is restored, and the polar components are removed from the oil. This process removes acid and water in addition to another compounds. Another advantage is that the oil may be re-used, and in most conditions, this can be accomplished with out switching off the unit, which contributes to cost-saving. If doubtful – instead change off the unit during this therapy process.
If the values are Poor, it is advisable to take action as soon as attainable and not delay the upkeep process. Excess water in the transformer system decreases the projected transformer lifetime considerably; extremely excessive water content may 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 check
This is a routine test for all lessons of electrical gear, besides class G
The outcomes of this check should always be thought-about at the facet of the breakdown power. If it is found that the water content material is high and the breakdown energy is low, additional motion must be taken. It is recommended that a second pattern from the identical unit is tested to verify the outcomes.
In the case of switching gear, the place there is not a paper present, the breakdown voltage is the figuring out factor.
It must be famous that the limits indicated by IEC 60422 Edition four apply to transformers with operating temperatures between forty and 70 °C. If it is found that the unit’s working temperature is outdoors this temperature range, it’s best to check with Annex A of the standard.
When the worth obtained via analyses is GOOD, the normal sampling interval can be maintained, requiring no further action.
When the worth returns a FAIR end result, extra frequent sampling is really helpful. It can additionally be useful to think about different parameters just like the breakdown voltage, particle content material and DDF/resistivity, and acidity to determine on the motion to be carried out.
A POOR end result would require immediate action from the asset supervisor. This would possibly embody taking another pattern to verify the outcomes from the primary evaluation. If it is confirmed that the water content is excessive, the oil may be filtered; this process ought to take away a large portion of the moisture from the oil if applied correctly. Follow-up samples must be taken to ensure that the moisture content continues to be inside the required limits. The purpose is that the most good portion of the water is caught up within the paper system in the transformer. This moisture will transfer from the paper into the oil beneath circumstances that favour this movement. It could be found later that the oil in the water has increased again without any obvious purpose, but the supply can be the paper within the transformer.
A visible inspection is also beneficial to discover out if any water might move into the transformer or electrical gear through leaks. This downside could be more extreme if the transformer or electrical tools is exterior and never in a covered space.
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 zero.25>0.20
C<0.100.15 to zero.30>0.30
F, G Not a routine check
This is a routine take a look at for all classes besides F and G
The acids in oils are shaped because of chemical reactions between the oil, water, and paper. Higher temperatures or load will increase will assist 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 could lead to sludge formation, normally across the decrease elements of the transformer core. The sludge will finally type a semi-solid substance that’s extremely difficult to take away.
If the result is GOOD, the regular sampling interval can proceed.
In case of a FAIR result, the sampling interval must be decreased to fit the situation. Future analysis should embody a visible inspection of the oil for sediment and sludge.
If the result is POOR according to the prescribed values in IEC 60422 Edition 4.0, the asset supervisor might determine to reclaim the oil or replace it with new or reclaimed oil, whichever option might suit their necessities one of the best.
e) Dielectric Dissipation factor at 40Hz to 60Hz at 90° C
PropertyCategoryGoodFairPoor
Dielectric Dissipation factorAt 40Hz to 60Hz at 90°CO, A<0.100.10 to 0.20>0.20
B, C<0.one hundred.10 to 0.50>0.50
D<0.010.01 to 0.03>0.03
E<0.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, besides F and G
The dielectric dissipation issue or tan delta of this check supplies info relating to the extent of the dielectric losses in transformer oil. This test measures the inefficiency of insulating material.
When oil ages, we have the formation of polar compounds, leading to phase displacement and dielectric losses. Other impurities that might affect the dissipation factor embrace 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 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 really helpful 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 test
DC resistivity of the oil is amongst the key parameters to assess the transformer insulation situation; that is based mostly on the reality that DC resistance is sensitive to oil degradation.
When the result is FAIR, more frequent sampling and checking additional 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 unique value<40% of unique worth
This test is restricted to oils with this additive.
It would be advisable to contact the oil provider to verify the details 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 getting older course of within the oil and the stable insulation.
If the result is FAIR, it’s suggested to high up the inhibitor degree to the prescribed degree per provider directions. It is advised to make use of a subject skilled educated in the procedure to carry out this activity.
If the end result obtained is POOR, the advice for this situation would recommend that the end consumer continues to make use of the oil “uninhibited,” but this will likely lead to more fast degradation of both the liquid and solid 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 under 1000ppm. This would 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 underneath these circumstances just isn’t required, though it might add additional protection 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 stable, (rate of lower < 10/mg/kg/year)50-70mg/kg or<70mg/kg, with a significantrate of decrease of >10mg/kg/year<50 and decreasing at >10mg/kg/year
Passivators, also referred to as steel deactivators, react with reactive steel surfaces and dissolved metals similar to copper and silver and cut back 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 basic sorts, 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 more rapidly; this depletion might speed up when the oil is un-inhibited.
With GOOD outcomes, common pattern intervals could be maintained.
With FAIR results, maintain regular monitoring.
When POOR, it is advised to take away the oil or remove the source of corrosivity from the oil through special oil therapy.
I) Sediment and sludge
This isn’t a routine check.
It is advised that this test is performed when the oil outcomes indicate a high acid worth and the dissipation factor is near the unacceptable restrict.
The outcomes must be less than 0.02% by mass to be negligible. If the results return a worth of greater than 0.02% by mass, it’s suggested that it’s reclaimed; otherwise, an oil change is really helpful.
j) Interfacial pressure
This isn’t 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 take a look at
F, GNot Applicable
The interfacial rigidity between transformer oil and water reduces through the aging process. What this means in sensible terms is there is extra polar compound present within the oil, decreasing the power of an oil to serve as an insulator within the transformer system. There is a direct correlation between interfacial rigidity and neutralisation quantity. Therefore, the interfacial rigidity becomes a quality criterion: the oil should be modified under a predefined limit.
If outcomes are GOOD, continue the regular sampling interval.
If results are FAIR, decrease the sampling interval.
If results are POOR, examine the oil for sediment and/or sludge.
k) Corrosive sulfur
This just isn’t a routine check.
Oil is either corrosive or non-corrosive.
The presence of corrosive sulfur in transformer oil and its effect on the transformer system could be significant. The extent of the corrosion harm caused by the sulfur may be so severe that it might trigger failure of the tools if not checked. The addition of a copper passivator can scale back the impression of this compound on the transformer system.
In a research by Doble, it has been found 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 might contaminate the oil with corrosive sulfur.
CIGRE Brochure no 378, 2009 stipulates the necessity of corrective actions based on this institute’s risk evaluation examine. [4]
l) Particle counting and sizing
Table three: Particles
Table B.1 – Typical contamination ranges (particles) encountered on power transformer insulating oil as measured utilizing IEC 60970 [5]
m) Flashpoint ° C
Not a routine take a look at
If there is a most decrease in flashpoints by 10%, the gear might require additional inspection. This worth would possibly differ in numerous countries.
It is suggested to perform this test when an unusual odour is noticed, the unit has been refilled, or an inside fault has occurred.
n) PCB (Polychlorinated Biphenyls)
This test is not to decide the situation of the transformer; this could be a health and security influence test. PCB is hazardous to each people and the surroundings; it’s critical to test for PCBs after the retro fill of a transformer. It is also required whenever any upkeep has been carried out on the unit, and the potential for contamination is present. If PCB content exceeds the really helpful limits, the suitable motion needs to be taken.
Units with a PCB content material of greater than 50ppm require a fireplace security plan, environmental protection plan, and extra 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 proprietor.
Local regulatory our bodies outline the bounds.
o) DGA (Dissolved Gas Analysis)
As DGA is an intricate science with lots of information and interpretation, we are going to focus on this phenomenon in part II of the article. The limits for the different gases and the interpretation of this knowledge in accordance with international requirements might be discussed in detail, forming a half of the general well being score determination of the transformer.
Conclusion
Transformer situation monitoring is an interlaced, highly thrilling subject of study. In this text, we targeted on the forms of tests to determine the condition of the transformer, the critical values, and the really helpful actions.
The Health Index indication makes it attainable to see the supposed reliability of a selected unit at a particular date and time. This makes it attainable to ensure greatest follow software and optimised upkeep. It additionally make it easier to attract up a upkeep plan and action plan.
References:
1. IEC 60422 Edition 4.0 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
three. Passivators, what they are 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 strength.”
6. Article initially published by Transformer Technology Magazine Issue sixteen – December 2021 https://www.transformer-technology.com
Author bio:
Corné Dames is a WearCheck transformer consultant. She has 20+ years’ expertise in the business, having previously worked as laboratory supervisor for a serious industrial laboratory group, specializing in transformer health. She has been intrigued by transformer chemistry proper from the start of her profession, notably in the analysis of check data. Corné has huge practical and theoretical information of reliability upkeep programmes.
Share

Leave a Comment