TALKING TRANSFORMER TESTING
by Brenna ShumbamhiniJune 9, 2022
Condition monitoring is the frequent accumulating, measuring, recording, and analysis of the related data relating to an asset’s operation. If we interpret the data correctly, it can provide us great perception into the asset’s situation.
Frequent monitoring of the asset can lead to less upkeep required or extra prolonged durations without any upkeep required.
It is essential to establish the vital thing parameters that are wanted to provide us a complete image of the particular standing of the transformer and the motion we want to take to ensure the continued reliability of the asset to realize the utmost lifetime.
What is the data telling us?
Has the situation of the unit modified because the last maintenance period?
Is it protected to operate 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 before we have to think about replacement?
Are the identified problems of a recurring nature?
Effective situation monitoring outline
It is vitally necessary to identify clear goals as a part of your strategy. What do you want to obtain 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 would be much simpler to identify the required parameters.
Health indexing of property is turning into a remarkable tool in getting a clearer picture of the condition of your transformer. Test parameters carry a numerical value-adding to the whole value of the Health Index Value of the transformer. These parameter weight values have been calculated primarily based on the worldwide requirements for mineral oils, indicating the important values stipulated within the varied requirements.
The scope of oil analysis, interpretation of the information, and critical values
At the beginning of this section, it’s important to state that we deal with different measurement transformers within the business. Transformers are divided into courses based on the kV scores of the gear. It is up to the reliability or asset manager to use the rules for larger gear, thereby implementing shorter increment oil evaluation and electrical exams.
The maintenance engineer or manager wants to discover out what sort of testing would benefit him in figuring out drawback areas inside his fleet. Some of the analysis has been recognized as to routine type tests. Still, there might be ราคาเกจวัดแรงดันน้ำ of tests that can help in identifying particular drawback standards within the system, which might not be clear by way of the typical day-to-day analysis normally performed.
Please see the rating lessons in TABLE 1
TABLE 1 FIG
TABLE 2 explains which oil analyses are recommended and the way usually or under which circumstances.
TABLE 2 FIG
The taking of the oil pattern is amongst the most vital and significant influencers within the evaluation end result. If a sample isn’t taken to the prescribed procedure, then there’s a important risk that the analysis carried out, and the results acquired, are of no use.
Care must be taken to make sure quality control 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 proper procedure is important. A pattern may be contaminated by numerous factors, all of which can influence the finish result of the leads to a negative method.
All steps involved in pattern taking should adhere to high quality control procedures, including the container that is used, the sampling package, the taking of the pattern, the marking of the pattern, the closing of the pattern, the storage and dealing with of the pattern, and then the delivery of the sample to the laboratory.
If the pattern identification and sample information are handwritten, the human issue can lead to incorrect interpretation of the information. The label should be stuck 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 put in writing on the label should be oil- and water-resistant. Otherwise, some knowledge might be misplaced, making it extraordinarily tough for the laboratory personnel to complete the report or allocate the pattern to a particular transformer.
Now, let’s talk about the forms of checks to determine the transformer’s condition, the critical values, and the recommended actions in each case:
a) Colour and look
This is a routine inspection utilized to every oil pattern.
When an oil sample arrives on the laboratory, one of the “tests” is a visible inspection of the oil pattern in a transparent vessel to find out the colour, turbidity, and attainable particle identification.
Dark oils might point out chemical degradation or contamination of the oil.
When there is plenty of turbidity, it’d indicate a high water content within the oil.
If the drain valve was not cleaned by the sampler, the filth particles within the drain valve might be integrated into the sample. If particles are recognized as carbon, it might indicate a potential electrical fault in the unit. The DGA evaluation of the oil will confirm if so.
Clear oils with out contamination will point out a great situation, and no action is recommended.
When oils are dark or turbid, additional evaluation will confirm any problems. The oil evaluation outcomes may even determine the degree and kind of motion.
b) Breakdown Voltage
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
This is a routine inspection.
Breakdown voltage will indicate 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 in the unit, the breakdown voltage should be excessive.
If the values are Good, it is strongly recommended to proceed with the present sample interval motion plan.
If the values are Fair, extra frequent sampling is recommended in collaboration with different parameter results like the water content material, DDF (dielectric dissipation factor), and acidity.
If values are Poor – it is recommended to recondition the oil through oil reconditioning processes. If different exams indicate extreme aging, the oil could be changed with new or reclaimed oil. Another option could be to carry out on-site oil reclamation utilizing a reclamation plant.
Reclamation of oil has the benefit that the colour of the oil is restored, and the polar parts are removed from the oil. This process removes acid and water as properly as another compounds. Another advantage is that the oil may be re-used, and in most conditions, this may be done with out switching off the unit, which contributes to cost-saving. If in doubt – instead change off the unit throughout this remedy process.
If the values are Poor, it’s advisable to take action as quickly as possible and never delay the maintenance process. Excess water within the transformer system decreases the projected transformer lifetime considerably; extraordinarily high water content material can cause flashover within the unit, leading to loss of the asset.
c) Water content material (mg/kg at transformer operating temperature)
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 check for all courses of electrical gear, except class G
The outcomes of this check should always be thought-about in conjunction with the breakdown energy. If it is discovered that the water content material is high and the breakdown energy is low, additional action must be taken. It is beneficial that a second pattern from the identical unit is examined to verify the results.
In the case of switching equipment, the place there isn’t any paper current, the breakdown voltage is the determining factor.
It ought to be famous that the boundaries indicated by IEC 60422 Edition 4 apply to transformers with operating temperatures between forty and 70 °C. If it’s found that the unit’s working temperature is outdoors this temperature range, it’s best to refer to Annex A of the usual.
When the worth obtained via analyses is GOOD, the traditional sampling interval can be maintained, requiring no additional action.
When the value returns a FAIR outcome, extra frequent sampling is recommended. It can additionally be useful to consider different parameters like the breakdown voltage, particle content and DDF/resistivity, and acidity to resolve on the motion to be carried out.
A POOR end result would require quick action from the asset manager. This would possibly embody taking one other pattern to verify the outcomes from the first analysis. If it is confirmed that the water content material is excessive, the oil can be filtered; this process should remove a large portion of the moisture from the oil if utilized correctly. Follow-up samples have to be taken to make certain that the moisture content remains to be throughout the required limits. The cause is that 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 circumstances that favour this movement. It might be found later that the oil in the water has increased once more with none obvious reason, however the source would be the paper within the transformer.
A visual inspection is also beneficial to discover out if any water would possibly transfer into the transformer or electrical tools by way of leaks. This downside could be extra extreme if the transformer or electrical equipment is outside and not in a covered space.
d) Acidity (mgKOH/g oil) Neutralization Number
Acidity mgKOH/g oilO, A, D<0.100.10 to 0.15>0.15
B, E<0.a hundred.10 to 0.25>0.20
C<0.one hundred.15 to 0.30>0.30
F, G Not a routine take a look at
This is a routine check for all classes except F and G
The acids in oils are formed as a outcome 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’ll adversely affect the insulation properties of the oil and can improve paper degradation. If left untreated in transformers, this can lead to sludge formation, usually across the lower elements of the transformer core. The sludge will eventually kind a semi-solid substance that’s extraordinarily difficult to take away.
If the result’s GOOD, the regular sampling interval can proceed.
In case of a FAIR result, the sampling interval must be decreased to fit the scenario. Future analysis should embody a visual inspection of the oil for sediment and sludge.
If the result is POOR in accordance with the prescribed values in IEC 60422 Edition 4.0, the asset manager might determine to reclaim the oil or exchange it with new or reclaimed oil, whichever possibility might swimsuit their necessities the most effective.
e) Dielectric Dissipation factor at 40Hz to 60Hz at 90° C
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 0.50>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 test
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 check offers info concerning the extent of the dielectric losses in transformer oil. This check measures the inefficiency of insulating material.
When oil ages, we have the formation of polar compounds, resulting in part displacement and dielectric losses. Other impurities that may influence the dissipation factor embrace water, dissolved insulating resin, and paper.
When the result is FAIR, more frequent sampling and checking further parameters is beneficial.
When the result’s POOR, reclamation or an oil change is really helpful. The construction of the oil is broken, in impact 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
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 likely considered one of the key parameters to assess the transformer insulation situation; this is based on the reality that DC resistance is delicate to grease degradation.
When the result is FAIR, more frequent sampling and checking further parameters is beneficial.
When the result is POOR, reclamation or an oil change is recommended.
g) Inhibitor content percent
Inhibitor Content %AllRestricted to Inhibited oils,Consult oil supplier40% to 60% Of original value<40% of original value
This take a look at is restricted to oils with this additive.
It would be advisable to contact the oil supplier to confirm the primary points concerning components.
The two most typical 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 objective of the inhibitor is to stop oxygen from reacting with the oil. This considerably slows the growing older course of in the oil and the stable insulation.
If the result’s FAIR, it is advised to prime up the inhibitor degree to the prescribed stage per provider instructions. It is advised to use a field skilled skilled within the procedure to perform this process.
If the outcome obtained is POOR, the recommendation for this state of affairs would recommend that the end person continues to make use of the oil “uninhibited,” however this will likely lead to more speedy degradation of each the liquid and stable insulation.
It should be famous that some transformers already have a built-in oil preservation system; that is designed to maintain dissolved oxygen at levels below 1000ppm. This would 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 underneath these circumstances isn’t required, though it might add additional protection against oil oxidation if the preservation system ever fails. 
h) Passivator content
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 lowering at >10mg/kg/year
Passivators, also referred to as steel deactivators, react with reactive steel surfaces and dissolved metals such as copper and silver and cut back their fee of response with compounds within 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.
As the oil ages, the passivator might deplete extra quickly; this depletion may accelerate when the oil is un-inhibited.
With GOOD results, regular sample intervals could be maintained.
With FAIR outcomes, maintain common monitoring.
When POOR, it is suggested to take away the oil or remove the supply of corrosivity from the oil by way of special oil therapy.
I) Sediment and sludge
This isn’t a routine check.
It is suggested that this take a look at is performed when the oil outcomes indicate a excessive acid value and the dissipation issue is close to the unacceptable limit.
The results need to be lower than zero.02% by mass to be negligible. If the results return a price of more than zero.02% by mass, it is suggested that it’s reclaimed; in any other case, an oil change is beneficial.
j) Interfacial tension
This just isn’t a routine take a look at
Interfacial Tension (mN/m)O, A, B, C, DInhibited Uninhibited>28 >2522 to twenty-eight 20 to 25<22 <20
ENot a routine test
F, GNot Applicable
The interfacial tension between transformer oil and water reduces during the growing older course of. What this means in sensible terms is there’s more polar compound present within the oil, reducing the flexibility of an oil to serve as an insulator within the transformer system. There is a direct correlation between interfacial rigidity and neutralisation number. Therefore, the interfacial pressure turns into a excessive quality criterion: the oil have to be changed below a predefined restrict.
If outcomes are GOOD, continue the common sampling interval.
If results are FAIR, lower the sampling interval.
If results are POOR, check the oil for sediment and/or sludge.
k) Corrosive sulfur
This is not 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 could be important. The extent of the corrosion harm caused by the sulfur may be so severe that it might cause 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 found that rubber products utilized in transformers would possibly add to the corrosivity of the oil. Nitrile rubber gaskets and hoses not approved for oil filtration would possibly contaminate the oil with corrosive sulfur.
CIGRE Brochure no 378, 2009 stipulates the necessity of corrective actions based mostly on this institute’s danger assessment research. 
l) Particle counting and sizing
Table three: Particles
Table B.1 – Typical contamination ranges (particles) encountered on energy transformer insulating oil as measured using IEC 60970 
m) Flashpoint ° C
Not a routine test
If there’s a maximum lower in flashpoints by 10%, the tools might require additional inspection. This worth may differ in several nations.
It is suggested to perform this take a look at when an unusual odour is noticed, the unit has been refilled, or an internal fault has occurred.
n) PCB (Polychlorinated Biphenyls)
This test is to not determine the condition of the transformer; this is a health and security impression take a look at. PCB is hazardous to each humans and the setting; it is important to test for PCBs after the retro fill of a transformer. It is also required every time any maintenance has been accomplished on the unit, and the risk of contamination is current. If PCB content exceeds the recommended limits, the appropriate action must be taken.
Units with a PCB content of greater than 50ppm require a hearth security plan, environmental protection plan, and further precautionary measures when upkeep is completed. This oil must be changed, and the oil disposed of as hazardous waste, with a certificates of secure disposal issued to the equipment owner.
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 partly II of the article. The limits for the different gases and the interpretation of this knowledge according to international standards will be mentioned intimately, forming a part of the overall health rating dedication of the transformer.
Transformer condition monitoring is an interlaced, extremely exciting subject of research. In this article, we centered on the types of checks to discover out the situation of the transformer, the crucial values, and the beneficial actions.
The Health Index indication makes it possible to see the supposed reliability of a selected unit at a specific date and time. This makes it attainable to ensure greatest follow software and optimised maintenance. It additionally make it easier to draw up a upkeep plan and action plan.
1. IEC 60422 Edition four.0 2013-01 International Standard (Mineral insulating oils in electrical equipment – supervision and maintenance guide)
2. Oxidation inhibitor and reinhabiting oil-filled transformers, by Andy Shkolnik
3. 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 strength.”
6. Article initially printed by Transformer Technology Magazine Issue sixteen – December 2021 https://www.transformer-technology.com
Corné Dames is a WearCheck transformer consultant. She has 20+ years’ expertise within the trade, having beforehand labored as laboratory manager for a significant industrial laboratory group, focusing on transformer well being. She has been intrigued by transformer chemistry right from the start of her profession, notably within the evaluation of check data. Corné has vast practical and theoretical information of reliability upkeep programmes.