by Brenna ShumbamhiniJune 9, 2022
Corne Dames
Condition monitoring is the frequent amassing, measuring, recording, and analysis of the relevant information relating to an asset’s operation. If we interpret the information appropriately, it can give us nice perception into the asset’s condition.
Frequent monitoring of the asset can lead to less maintenance required or more extended durations with none maintenance required.
It is crucial to establish the necessary thing parameters which may be wanted to offer us an entire image of the actual standing of the transformer and the motion we want to take to make sure the continued reliability of the asset to achieve the maximum lifetime.
What is the info telling us?
Has the situation of the unit modified since the final maintenance period?
Is it protected to function the unit?
Are there indicators of deterioration?
Is it safe to load the unit above the nameplate rating for a selected period?
Are we required to implement motion to make sure the continued reliability of the unit?
How lengthy can we use the unit earlier than we need to think about replacement?
Are the recognized problems of a recurring nature?
Effective situation monitoring define
It is vitally important to determine clear targets as a part of your strategy. What do you wish to obtain by implementing this situation monitoring plan? Is it in-service failure prevention? Or possibly life extension? Maintenance deferral? By stipulating the outcome and what you want to accomplish, it might be much easier to determine the required parameters.
Health indexing of belongings is changing into a remarkable tool in getting a clearer picture of the situation 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 based on the worldwide requirements for mineral oils, indicating the important values stipulated within the various requirements.
The scope of oil analysis, interpretation of the data, and critical values
At the beginning of this section, it is essential to state that we cope with different measurement transformers within the industry. Transformers are divided into courses in accordance with the kV rankings of the gear. It is as a lot as the reliability or asset supervisor to use the rules for bigger gear, thereby implementing shorter increment oil evaluation and electrical exams.
The maintenance engineer or manager wants to discover out what type of testing would benefit him in identifying drawback areas within his fleet. Some of the evaluation has been recognized as to routine type tests. Still, there’s an extensive range of tests that may assist in figuring out particular downside criteria inside the system, which could not be clear by way of the standard day-to-day analysis usually carried out.
Please see the ranking lessons in TABLE 1
TABLE 2 explains which oil analyses are beneficial and the way typically or underneath which circumstances.
Oil sampling
The taking of the oil pattern is doubtless considered one of the most important and critical influencers in the evaluation consequence. If a pattern isn’t taken to the prescribed procedure, then there’s a important possibility that the analysis performed, and the outcomes acquired, are of no use.
Care ought to be taken to make sure quality management procedures are utilized in each step of the sampling course of as set out by international standards. A good quality sample taken by applying the right procedure is essential. A sample can be contaminated by numerous components, all of which might affect the result of the results in a unfavorable manner.
All steps involved in pattern taking must adhere to quality management procedures, including the container that’s used, the sampling equipment, the taking of the sample, the marking of the sample, the closing of the pattern, the storage and handling of the sample, after which the delivery of the pattern to the laboratory.
If the pattern identification and pattern information are handwritten, the human issue can lead to incorrect interpretation of the info. The label must be caught onto the container to make sure no mix-ups in pattern identification. Ensure that the label is completed in neat, easy-to-read handwriting. The label should be waterproof, and the pen used to write on the label should be oil- and water resistant. Otherwise, some information may be misplaced, making it extremely tough for the laboratory personnel to complete the report or allocate the pattern to a particular transformer.
Now, let’s discuss the kinds of checks to discover out the transformer’s situation, the important values, and the recommended actions in each case:
a) Colour and look
This is a routine inspection utilized to each oil sample.
When an oil pattern arrives at the laboratory, one of the “tests” is a visual inspection of the oil sample in a transparent vessel to find out the colour, turbidity, and possible particle identification.
Dark oils might point out chemical degradation or contamination of the oil.
When there is lots of turbidity, it’d point out a high water content within the oil.
If the drain valve was not wiped clean by the sampler, the dirt particles within the drain valve may be integrated into the sample. If particles are identified as carbon, it might point out a possible electrical fault within the unit. The DGA analysis of the oil will affirm if that’s so.
Clear oils without contamination will point out a great situation, and no motion is recommended.
When oils are darkish or turbid, further analysis will confirm any issues. The oil evaluation outcomes may even determine the diploma and sort of action.
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 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 or the presence of foreign particles, or both in 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 have to be high.
If the values are Good, it is strongly recommended to continue with the current sample interval motion plan.
If the values are Fair, extra frequent sampling is really helpful in collaboration with other parameter results just 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 alternative exams point out severe getting older, the oil could be replaced with new or reclaimed oil. เกจวัดแก๊สหุงต้ม can be to carry out on-site oil reclamation utilizing 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 process 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 can be done without switching off the unit, which contributes to cost-saving. If doubtful – as a substitute change off the unit during this therapy course of.
If the values are Poor, it is advisable to take motion as soon as potential and never delay the upkeep course of. Excess water in the transformer system decreases the projected transformer lifetime significantly; extraordinarily high water content material can cause flashover in the unit, resulting in loss of the asset.
c) Water content (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 take a look at
This is a routine test for all lessons of electrical gear, besides class G
The outcomes of this check ought to always be thought of along side the breakdown energy. If it’s found that the water content is high and the breakdown energy is low, further motion needs to be taken. It is really helpful that a second sample from the identical unit is tested to substantiate the outcomes.
In the case of switching equipment, where there isn’t any paper current, the breakdown voltage is the determining issue.
เกจวัดแรงดันแก๊ส 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 is discovered that the unit’s working temperature is outside this temperature range, it’s best to check with Annex A of the standard.
When the worth obtained via analyses is GOOD, the conventional sampling interval can be maintained, requiring no additional action.
When the value returns a FAIR outcome, more frequent sampling is really helpful. It can also be useful to contemplate other parameters like the breakdown voltage, particle content and DDF/resistivity, and acidity to determine on the motion to be implemented.
A POOR result would require quick motion from the asset manager. This might embrace taking another pattern to verify the results from the primary analysis. If it’s confirmed that the water content is high, the oil may be filtered; this process should take away a big portion of the moisture from the oil if applied accurately. Follow-up samples have to be taken to ensure that the moisture content remains to be inside the required limits. The reason is that probably the most significant portion of the water is caught up within the paper system within the transformer. This moisture will move from the paper into the oil under conditions that favour this movement. It could be discovered later that the oil in the water has increased once more without any apparent cause, but the supply could be the paper in the transformer.
A visual inspection can also be really helpful to determine if any water might move into the transformer or electrical tools via leaks. This problem could be more extreme if the transformer or electrical tools is outside and never in a coated space.
d) Acidity (mgKOH/g oil) Neutralization Number
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< hundred.15 to zero.30>0.30
F, G Not a routine test
This is a routine take a look at for all lessons besides F and G
The acids in oils are fashioned due to chemical reactions between the oil, water, and paper. Higher temperatures or load increases will assist within the formation of the acids. Because acids are polar compounds, it’s going to adversely have an effect on the insulation properties of the oil and can enhance paper degradation. If left untreated in transformers, this will result in sludge formation, often around the decrease parts of the transformer core. The sludge will finally form a semi-solid substance that is extremely troublesome to remove.
If the result is GOOD, the common sampling interval can proceed.
In case of a FAIR result, the sampling interval should be decreased to suit the situation. Future analysis should embrace a visual inspection of the oil for sediment and sludge.
If the result’s POOR based on the prescribed values in IEC 60422 Edition, the asset manager may resolve to reclaim the oil or replace it with new or reclaimed oil, whichever choice would possibly suit their requirements the most effective.
e) Dielectric Dissipation issue at 40Hz to 60Hz at 90° C
Dielectric Dissipation factorAt 40Hz to 60Hz at 90°CO, A< hundred.10 to zero.20>0.20
B, C<0.a hundred.10 to zero.50>0.50
D<0.010.01 to 0.03>0.03
E< hundred.01 to zero.30>0.03
F, GNot a routine check
This is a routine test for all classes of electrical tools, besides F and G
The dielectric dissipation issue or tan delta of this check offers information concerning the extent of the dielectric losses in transformer oil. This take a look at measures the inefficiency of insulating materials.
When oil ages, we’ve the formation of polar compounds, leading to part displacement and dielectric losses. Other impurities that may affect the dissipation factor embrace water, dissolved insulating resin, and paper.
When the result’s FAIR, more frequent sampling and checking further parameters is really helpful.
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 damaged down, and even with filtration, the really helpful dielectric values can’t be achieved.
f) Resistivity (GΩm) at 20 °C or ninety °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 check
DC resistivity of the oil is certainly one of the key parameters to assess the transformer insulation condition; this is primarily based on the fact that DC resistance is delicate to grease degradation.
When the result is FAIR, more frequent sampling and checking additional parameters is beneficial.
When the result is POOR, reclamation or an oil change is recommended.
g) Inhibitor content material %
Inhibitor Content %AllRestricted to Inhibited oils,Consult oil supplier40% to 60% Of authentic value<40% of original worth
This test is restricted to oils with this additive.
It would be advisable to contact the oil provider to confirm the small print regarding additives.
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 growing older process in the oil and the stable insulation.
If the result is FAIR, it is advised to prime up the inhibitor degree to the prescribed degree per provider directions. It is suggested to make use of a subject skilled educated in the process to carry out this activity.
If the result obtained is POOR, the recommendation for this situation would suggest that the tip user continues to make use of the oil “uninhibited,” but this may result in more speedy degradation of each the liquid and solid insulation.
It must be noted that some transformers already have a built-in oil preservation system; this is designed to keep dissolved oxygen at levels beneath 1000ppm. This would 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 underneath these circumstances isn’t required, although it’d add additional safety against oil oxidation if the preservation system ever fails. [2]
h) Passivator content material
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 reducing at >10mg/kg/year
Passivators, also called steel deactivators, react with reactive metallic surfaces and dissolved metals such as copper and silver and reduce 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 types, sulfur-based and nitrogen-based. The first advised 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.[3]
As the oil ages, the passivator would possibly deplete extra quickly; this depletion might accelerate when the oil is un-inhibited.
With GOOD outcomes, regular sample intervals can be maintained.
With FAIR results, keep common monitoring.
When POOR, it’s suggested to take away the oil or take away the supply of corrosivity from the oil via special oil remedy.
I) Sediment and sludge
This is not a routine take a look at.
It is advised that this test is performed when the oil results point out a excessive acid value and the dissipation issue is near the unacceptable limit.
The outcomes must be lower than zero.02% by mass to be negligible. If the outcomes return a price of more than zero.02% by mass, it is advised that it’s reclaimed; otherwise, an oil change is really helpful.
j) Interfacial pressure
This just isn’t a routine test
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 tension between transformer oil and water reduces through the growing older course of. What this means in sensible terms is there is extra polar compound present in the oil, reducing the flexibility of an oil to function an insulator in the transformer system. There is a direct correlation between interfacial rigidity and neutralisation quantity. Therefore, the interfacial pressure becomes a quality criterion: the oil have to be modified under a predefined limit.
If outcomes are GOOD, proceed the common sampling interval.
If results are FAIR, decrease the sampling interval.
If outcomes are POOR, examine the oil for sediment and/or sludge.
k) Corrosive sulfur
This isn’t a routine test.
Oil is both corrosive or non-corrosive.
The presence of corrosive sulfur in transformer oil and its effect on the transformer system could be important. The extent of the corrosion harm caused by the sulfur can be so severe that it would trigger failure of the gear if not checked. The addition of a copper passivator can cut back the impression of this compound on the transformer system.
In a study by Doble, it has been found that rubber products used in transformers may 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 necessity of corrective actions based on this institute’s risk evaluation study. [4]
l) Particle counting and sizing
Table three: Particles
Table B.1 – Typical contamination ranges (particles) encountered on power transformer insulating oil as measured using IEC 60970 [5]
m) Flashpoint ° C
Not a routine check
If there is a maximum decrease in flashpoints by 10%, the gear would possibly require additional inspection. This value may differ in numerous international locations.
It is suggested to carry out this check when an uncommon odour is observed, the unit has been refilled, or an inside fault has occurred.
n) PCB (Polychlorinated Biphenyls)
This check is to not decide the situation of the transformer; this is a health and safety impression take a look at. 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 accomplished on the unit, and the potential for contamination is current. If PCB content material exceeds the really helpful limits, the appropriate motion must be taken.
Units with a PCB content material of more than 50ppm require a hearth security plan, environmental protection plan, and further precautionary measures when upkeep is completed. This oil needs to be changed, and the oil disposed of as hazardous waste, with a certificate of safe disposal issued to the equipment owner.
Local regulatory our bodies define the bounds.
o) DGA (Dissolved Gas Analysis)
As DGA is an intricate science with a lot of information and interpretation, we’ll talk about this phenomenon partly II of the article. The limits for the different gases and the interpretation of this data in accordance with international requirements shall be mentioned in detail, forming a half of the overall health rating dedication of the transformer.
Transformer condition monitoring is an interlaced, highly thrilling subject of study. In this text, we focused on the forms of exams to determine the situation of the transformer, the important values, and the recommended actions.
The Health Index indication makes it possible to see the supposed reliability of a specific unit at a selected date and time. This makes it potential to ensure greatest practice utility and optimised maintenance. It also make it simpler to draw up a maintenance plan and motion plan.
1. IEC 60422 Edition four.0 2013-01 International Standard (Mineral insulating oils in electrical gear – supervision and maintenance 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 published by Transformer Technology Magazine Issue sixteen – December 2021
Author bio:
Corné Dames is a WearCheck transformer consultant. She has 20+ years’ expertise in the industry, having previously labored as laboratory manager for a major industrial laboratory group, specializing in transformer health. She has been intrigued by transformer chemistry right from the start of her profession, particularly in the analysis of take a look at data. Corné has vast sensible and theoretical information of reliability maintenance programmes.

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