by Brenna ShumbamhiniJune 9, 2022
Corne Dames
Condition monitoring is the frequent accumulating, measuring, recording, and evaluation of the related information concerning an asset’s operation. If we interpret the data correctly, it can provide us great insight into the asset’s situation.
Frequent monitoring of the asset can lead to less maintenance required or extra extended durations without any upkeep required.
It is essential to determine the key parameters that are needed to give us a whole picture of the particular standing of the transformer and the motion we need to take to ensure the continued reliability of the asset to achieve the utmost lifetime.
What is the data telling us?
Has the condition of the unit changed since the final maintenance period?
Is it protected to operate the unit?
Are there signs of deterioration?
Is it protected to load the unit above the nameplate score for a particular 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 issues of a recurring nature?
Effective situation monitoring define
It is vitally essential to identify clear objectives as part of your strategy. What do you need to achieve by implementing this situation monitoring plan? Is it in-service failure prevention? Or perhaps life extension? Maintenance deferral? By stipulating the result and what you wish to accomplish, it would be much simpler to establish the required parameters.
Health indexing of assets is becoming a exceptional device in getting a clearer image of the situation of your transformer. Test parameters carry a numerical value-adding to the whole worth of the Health Index Value of the transformer. These parameter weight values had been calculated primarily based on the worldwide requirements for mineral oils, indicating the crucial values stipulated in the various requirements.
The scope of oil evaluation, interpretation of the data, and critical values
At the start of this part, it is essential to state that we deal with completely different measurement transformers within the business. Transformers are divided into classes according to the kV scores of the gear. It is as a lot as the reliability or asset manager to use the rules for bigger tools, thereby implementing shorter increment oil evaluation and electrical tests.
The upkeep engineer or supervisor wants to determine what sort of testing would benefit him in identifying problem areas within his fleet. Some of the analysis has been identified as to routine sort exams. Still, there is an intensive range of checks that can assist in figuring out specific problem criteria within the system, which could not be clear via the everyday day-to-day analysis normally carried out.
Please see the ranking lessons in TABLE 1
TABLE 2 explains which oil analyses are recommended and the way usually or under which circumstances.
Oil sampling
The taking of the oil pattern is among the most important and important influencers within the analysis consequence. If a sample is not taken to the prescribed procedure, then there is a important possibility that the analysis carried out, and the outcomes acquired, are of no use.
Care must be taken to ensure quality management procedures are utilized in every step of the sampling course of as set out by international standards. A good high quality pattern taken by making use of the right process is important. A pattern could be contaminated by numerous components, all of which can influence the outcome of the leads to a unfavorable manner.
All steps concerned in pattern taking must adhere to high quality control procedures, together with the container that’s used, the sampling package, the taking of the sample, the marking of the pattern, the closing of the pattern, the storage and handling of the sample, after which the delivery of the pattern to the laboratory.
If the sample identification and sample knowledge are handwritten, the human issue can lead to incorrect interpretation of the data. The label ought to be stuck 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 ought to be waterproof, and the pen used to write down on the label must be oil- and water-resistant. Otherwise, some knowledge may be misplaced, making it extraordinarily tough for the laboratory personnel to finish the report or allocate the pattern to a particular transformer.
Now, let’s focus on the forms of tests to find out the transformer’s condition, the critical values, and the beneficial actions in each case:
a) Colour and look
This is a routine inspection applied to each oil pattern.
When an oil sample arrives on the laboratory, one of many “tests” is a visible inspection of the oil pattern in a clear vessel to discover out the colour, turbidity, and attainable particle identification.
Dark oils may indicate chemical degradation or contamination of the oil.
When there’s plenty of turbidity, it might indicate a excessive 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 included into the sample. If particles are identified as carbon, it might point out a possible electrical fault in the unit. The DGA evaluation of the oil will affirm if that is so.
Clear oils without contamination will indicate 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 may even decide the diploma and type 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 application
G <30
This is a routine inspection.
Breakdown voltage will indicate the water content material or the presence of foreign particles, or each in the oil being analysed.
As the oil in transformers acts as an insulation medium to avoid flashover within 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 motion 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 suggested to recondition the oil by way of oil reconditioning processes. If alternative exams point out extreme growing older, the oil may 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 benefit that the colour of the oil is restored, and the polar components are removed from the oil. This process removes acid and water as properly as another compounds. Another benefit is that the oil can be re-used, and in most conditions, this may be carried out without switching off the unit, which contributes to cost-saving. If unsure – as a substitute change off the unit during this therapy course of.
If the values are Poor, it is advisable to take motion as quickly as attainable and never delay the maintenance process. Excess water in the transformer system decreases the projected transformer lifetime considerably; extraordinarily high water content can cause flashover within the unit, leading to lack 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 take a look at
This is a routine test for all classes of electrical equipment, besides class G
The outcomes of this take a look at should always be thought of in conjunction with the breakdown strength. If it is discovered that the water content material is excessive and the breakdown power is low, further motion must be taken. It is really helpful that a second pattern from the same unit is tested to verify the results.
In the case of switching tools, the place there isn’t a paper present, the breakdown voltage is the figuring out factor.
It must be famous that the bounds indicated by IEC 60422 Edition four apply to transformers with working temperatures between forty and 70 °C. If it’s found that the unit’s working temperature is outdoors this temperature vary, it’s best to check with Annex A of the usual.
When the value obtained through analyses is GOOD, the traditional sampling interval can be maintained, requiring no further motion.
When the worth returns a FAIR outcome, more frequent sampling is beneficial. It can be useful to contemplate different parameters just like the breakdown voltage, particle content and DDF/resistivity, and acidity to resolve on the action to be carried out.
A POOR outcome will require instant motion from the asset manager. This would possibly include taking one other pattern to verify the results from the primary analysis. If it is confirmed that the water content is high, the oil could be filtered; this process ought to remove a large portion of the moisture from the oil if utilized accurately. Follow-up samples must be taken to make sure that the moisture content continues to be within the required limits. The purpose is that probably 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 conditions that favour this movement. It may be found later that the oil within the water has elevated again without any apparent cause, however the supply can be the paper in the transformer.
A visible inspection is also recommended to discover out if any water might move into the transformer or electrical equipment via leaks. This problem might be extra extreme if the transformer or electrical equipment is outdoors and never in a coated area.
d) Acidity (mgKOH/g oil) Neutralization Number
Acidity mgKOH/g oilO, A, D<0.100.10 to zero.15>0.15
B, E<0.100.10 to 0.25>0.20
C< hundred.15 to 0.30>0.30
F, G Not a routine check
This is a routine take a look at for all classes except F and G
The acids in oils are formed because of 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 will adversely affect the insulation properties of the oil and will improve paper degradation. If left untreated in transformers, this can lead to sludge formation, usually across the decrease elements of the transformer core. The sludge will finally kind a semi-solid substance that is extremely difficult to take away.
If the result’s GOOD, the regular sampling interval can continue.
In case of a FAIR outcome, the sampling interval ought to be decreased to fit the state of affairs. Future analysis ought to 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 may resolve to reclaim the oil or replace it with new or reclaimed oil, whichever option would possibly swimsuit their necessities the most effective.
e) Dielectric Dissipation issue at 40Hz to 60Hz at 90° C
Dielectric Dissipation factorAt 40Hz to 60Hz at 90°CO, A<0.100.10 to 0.20>0.20
B, C< hundred.10 to zero.50>0.50
D<0.010.01 to 0.03>0.03
E< hundred.01 to 0.30>0.03
F, GNot a routine take a look at
This is a routine test for all classes of electrical tools, besides F and G
The dielectric dissipation issue or tan delta of this test provides information regarding 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 part displacement and dielectric losses. Other impurities which may influence the dissipation factor embrace water, dissolved insulating resin, and paper.
When the result’s FAIR, more frequent sampling and checking further parameters is beneficial.
When the result is POOR, reclamation or an oil change is recommended. The construction of the oil is broken, in effect that the chemical bonds between the molecules have damaged down, and even with filtration, the beneficial 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 evaluate the transformer insulation condition; that is based on the truth that DC resistance is delicate to oil degradation.
When the result’s FAIR, more frequent sampling and checking further parameters is recommended.
When the result is POOR, reclamation or an oil change is beneficial.
g) Inhibitor content material %
Inhibitor Content %AllRestricted to Inhibited oils,Consult oil supplier40% to 60% Of authentic value<40% of unique value
This check is restricted to oils with this additive.
It could be advisable to contact the oil provider to verify the small print concerning 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 function of the inhibitor is to forestall oxygen from reacting with the oil. This considerably slows the growing older course of within the oil and the solid insulation.
If the result’s FAIR, it is advised to top up the inhibitor stage to the prescribed degree per supplier directions. It is suggested to use a subject professional educated within the procedure to perform this task.
If the end result obtained is POOR, the recommendation for this state of affairs would recommend that the top person continues to use the oil “uninhibited,” however this will lead to more rapid degradation of each the liquid and stable insulation.
It ought to be noted that some transformers have already got a built-in oil preservation system; that is designed to keep dissolved oxygen at ranges beneath 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 underneath these circumstances is not required, although it would add extra protection towards 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 stable, (rate of decrease < 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 identified as steel deactivators, react with reactive metallic surfaces and dissolved metals corresponding to copper and silver and scale back their price of reaction with compounds in the oil. This consists of oxidation reactions with organic 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 creator 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 may deplete more rapidly; this depletion might accelerate when the oil is un-inhibited.
With GOOD results, common sample intervals can be maintained.
With FAIR results, preserve common monitoring.
When POOR, it is suggested to take away the oil or take away the supply of corrosivity from the oil by way of special oil remedy.
I) Sediment and sludge
This just isn’t a routine test.
It is suggested that this check is carried out when the oil outcomes point out a high acid value and the dissipation factor is near the unacceptable limit.
The results need to be lower than 0.02% by mass to be negligible. If the outcomes return a worth of more than 0.02% by mass, it’s instructed that it be reclaimed; otherwise, an oil change is really helpful.
j) Interfacial rigidity
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 check
F, GNot Applicable
The interfacial rigidity between transformer oil and water reduces through the getting older course of. What this implies in practical phrases is there’s extra polar compound present within the oil, lowering the ability of an oil to serve as an insulator in the transformer system. There is a direct correlation between interfacial tension and neutralisation quantity. Therefore, the interfacial pressure becomes a prime quality criterion: the oil have to be modified beneath a predefined restrict.
If results are GOOD, continue the common sampling interval.
If outcomes are FAIR, decrease the sampling interval.
If results are POOR, verify 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 impact on the transformer system may be vital. The extent of the corrosion damage caused by the sulfur can be so severe that it’d trigger failure of the tools if not checked. The addition of a copper passivator can reduce the impact of this compound on the transformer system.
In a study by Doble, it has been discovered that rubber merchandise used in transformers might add to the corrosivity of the oil. Nitrile rubber gaskets and hoses not permitted for oil filtration may contaminate the oil with corrosive sulfur.
CIGRE Brochure no 378, 2009 stipulates the need of corrective actions primarily based on this institute’s danger evaluation 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 is a maximum lower in flashpoints by 10%, the tools may require additional inspection. เกจวัดแรงดันน้ำไทวัสดุ would possibly differ in several nations.
It is advised to carry out this check when an uncommon odour is seen, the unit has been refilled, or an internal fault has occurred.
n) PCB (Polychlorinated Biphenyls)
This check is to not decide the situation of the transformer; this can be a health and safety impact check. PCB is hazardous to each humans and the setting; it is vital to check for PCBs after the retro fill of a transformer. It can additionally be required each time any upkeep has been accomplished on the unit, and the chance of contamination is present. If PCB content exceeds the recommended limits, the suitable motion needs to be taken.
Units with a PCB content material of more than 50ppm require a fireplace safety plan, environmental protection plan, and further precautionary measures when upkeep is finished. This oil needs to be changed, and the oil disposed of as hazardous waste, with a certificate of protected disposal issued to the tools proprietor.
Local regulatory our bodies define the limits.
o) DGA (Dissolved Gas Analysis)
As DGA is an intricate science with a lot of information and interpretation, we’ll discuss this phenomenon partially II of the article. The limits for the completely different gases and the interpretation of this knowledge in accordance with international standards shall be discussed in detail, forming part of the overall well being ranking determination of the transformer.
Transformer condition monitoring is an interlaced, extremely thrilling subject of examine. In this article, we focused on the forms of exams to determine the condition of the transformer, the important values, and the recommended 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 potential to make sure best follow software and optimised maintenance. It additionally make it simpler to attract up a maintenance plan and action plan.
1. IEC 60422 Edition 2013-01 International Standard (Mineral insulating oils in electrical gear – supervision and maintenance guide)
2. pressure gauge ด้าน ดูด and reinhabiting oil-filled transformers, by Andy Shkolnik
3. Passivators, what they’re and the way 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 revealed by Transformer Technology Magazine Issue sixteen – December 2021
Author bio:
Corné Dames is a WearCheck transformer marketing consultant. She has 20+ years’ experience within the industry, having beforehand labored as laboratory manager for a major industrial laboratory group, focusing on transformer health. She has been intrigued by transformer chemistry proper from the start of her career, particularly within the analysis of check data. Corné has vast sensible and theoretical information of reliability maintenance programmes.

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