by Brenna ShumbamhiniJune 9, 2022
Corne Dames
Condition monitoring is the frequent amassing, measuring, recording, and analysis of the related knowledge regarding an asset’s operation. If we interpret the data correctly, it can provide us great perception into the asset’s condition.
Frequent monitoring of the asset can result in much less upkeep required or extra prolonged periods without any maintenance required.
It is essential to determine the vital thing parameters that are needed to provide us an entire image of the particular status of the transformer and the action we have to take to ensure the continued reliability of the asset to attain the utmost lifetime.
What is the data telling us?
Has the condition of the unit changed for the explanation that last maintenance period?
Is it secure to operate the unit?
Are there indicators of deterioration?
Is it safe to load the unit above the nameplate rating for a particular period?
Are we required to implement action to make sure the continued reliability of the unit?
How long can we use the unit earlier than we need to consider replacement?
Are the identified problems of a recurring nature?
Effective condition monitoring outline
It is vitally important to identify clear goals as part of your technique. What do you want to achieve by implementing this situation monitoring plan? Is it in-service failure prevention? Or perhaps life extension? Maintenance deferral? By stipulating the finish result and what you want to accomplish, it would be much easier to establish the required parameters.
Health indexing of belongings is becoming a exceptional device in getting a clearer picture of the situation 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 had been calculated based on the worldwide requirements for mineral oils, indicating the important values stipulated in the various requirements.
The scope of oil analysis, interpretation of the information, and critical values
At the start of this section, it’s important to state that we deal with different size transformers within the industry. Transformers are divided into courses according to the kV rankings of the equipment. It is as much as the reliability or asset supervisor to use the guidelines for larger gear, thereby implementing shorter increment oil analysis and electrical tests.
The upkeep engineer or manager wants to find out what kind of testing would benefit him in figuring out problem areas within his fleet. Some of the evaluation has been identified as to routine type exams. Still, there’s an in depth vary of tests that may help in figuring out specific drawback standards throughout the system, which could not be clear by way of the everyday day-to-day analysis usually carried out.
Please see the ranking classes in TABLE 1
TABLE 2 explains which oil analyses are recommended and how usually or underneath which circumstances.
Oil sampling
The taking of the oil sample is likely certainly one of the most important and important influencers in the analysis end result. If a sample just isn’t taken to the prescribed procedure, then there’s a significant possibility that the analysis performed, and the results acquired, are of no use.
Care should be taken to make sure quality control procedures are applied in each step of the sampling course of as set out by international requirements. A good quality pattern taken by making use of the proper procedure is crucial. A pattern could be contaminated by numerous components, all of which can affect the result of the ends in a adverse manner.
All steps concerned in sample taking must adhere to quality management procedures, including the container that’s used, the sampling kit, the taking of the sample, the marking of the sample, the closing of the sample, the storage and handling of the pattern, after which the supply of the pattern to the laboratory.
If the pattern identification and sample information are handwritten, the human factor can result in incorrect interpretation of the data. The label ought to be stuck onto the container to ensure 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 put in writing on the label should be oil- and waterproof. Otherwise, some knowledge may be misplaced, making it extremely troublesome for the laboratory personnel to complete the report or allocate the sample to a selected transformer.
Now, let’s discuss the kinds of tests to determine the transformer’s situation, the important values, and the beneficial actions in every case:
a) Colour and look
This is a routine inspection utilized to each oil sample.
When an oil pattern arrives on the laboratory, one of many “tests” is a visible inspection of the oil pattern in a transparent vessel to discover out the color, turbidity, and potential particle identification.
Dark oils may point out chemical degradation or contamination of the oil.
When there could be a lot of turbidity, it might point out a high water content material within the oil.
If the drain valve was not wiped clean by the sampler, the filth particles in the drain valve may be incorporated into the pattern. If particles are recognized as carbon, it would point out a potential electrical fault within the unit. The DGA evaluation of the oil will confirm if that is so.
Clear oils with out contamination will indicate a good condition, and no motion is really helpful.
When oils are dark or turbid, additional evaluation will confirm any issues. The oil evaluation results may even determine the diploma 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 application
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 avoid flashover in the unit, the breakdown voltage should be excessive.
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 really helpful in collaboration with other parameter outcomes just 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 tests indicate severe growing older, the oil could be replaced with new or reclaimed oil. Another choice would be to perform 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 elements are removed from the oil. This process removes acid and water in addition to another compounds. Another benefit is that the oil could be re-used, and in most situations, this may be done without switching off the unit, which contributes to cost-saving. If in doubt – as a substitute change off the unit throughout this therapy process.
If the values are Poor, it’s advisable to take motion as soon as potential and not delay the maintenance course of. Excess water within the transformer system decreases the projected transformer lifetime considerably; extraordinarily excessive water content material can cause flashover within the unit, resulting in 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 test
This is a routine test for all courses of electrical tools, except class G
The results of this check should all the time be thought of at the aspect of the breakdown power. If it’s 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 same unit is tested to confirm the outcomes.
In the case of switching gear, the place there isn’t a paper present, the breakdown voltage is the figuring out issue.
It ought to be noted that the limits indicated by IEC 60422 Edition 4 apply to transformers with operating temperatures between forty and 70 °C. If it’s discovered that the unit’s working temperature is exterior this temperature range, it’s best to refer to Annex A of the usual.
When the worth obtained by way of analyses is GOOD, the conventional sampling interval can be maintained, requiring no further action.
When the worth returns a FAIR outcome, extra frequent sampling is beneficial. It can be helpful to consider different parameters just like the breakdown voltage, particle content and DDF/resistivity, and acidity to decide on the action to be applied.
A POOR end result would require instant action from the asset supervisor. This may embody taking one other pattern to substantiate the outcomes from the first analysis. If it is confirmed that the water content is high, the oil can be filtered; this process should remove a large portion of the moisture from the oil if applied correctly. Follow-up samples must be taken to ensure that the moisture content remains to be throughout the required limits. จำหน่ายเกจวัดแรงดัน is that probably the most significant slice of the water is caught up in the paper system in the transformer. This moisture will move from the paper into the oil under situations that favour this movement. It may be found later that the oil within the water has elevated again without any apparent reason, but the source could be the paper in the transformer.
A visual inspection can additionally be really helpful to find out if any water would possibly transfer into the transformer or electrical equipment through leaks. This downside could be extra extreme if the transformer or electrical tools is outdoors and never in a covered area.
d) Acidity (mgKOH/g oil) Neutralization Number
Acidity mgKOH/g oilO, A, D< hundred.10 to zero.15>0.15
B, E<0.a hundred.10 to 0.25>0.20
C<0.100.15 to 0.30>0.30
F, G Not a routine take a look at
This is a routine test for all classes 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 assist within the formation of the acids. Because acids are polar compounds, it will adversely affect the insulation properties of the oil and will enhance paper degradation. If left untreated in transformers, this can result in sludge formation, often around the lower parts of the transformer core. The sludge will finally form a semi-solid substance that is extremely troublesome to take away.
If the result is GOOD, the regular sampling interval can proceed.
In case of a FAIR end result, the sampling interval ought to be decreased to fit the situation. Future analysis should include a visible inspection of the oil for sediment and sludge.
If the result is POOR according to the prescribed values in IEC 60422 Edition, the asset supervisor might resolve to reclaim the oil or exchange it with new or reclaimed oil, whichever choice may 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<0.a hundred.10 to 0.20>0.20
B, C<0.100.10 to 0.50>0.50
D<0.010.01 to 0.03>0.03
E<0.a hundred.01 to zero.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 factor or tan delta of this test offers info relating to the extent of the dielectric losses in transformer oil. This take a look at measures the inefficiency of insulating materials.
When oil ages, we now have the formation of polar compounds, leading to section 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’s POOR, reclamation or an oil change is beneficial. The construction of the oil is broken, in effect that the chemical bonds between the molecules have broken down, and even with filtration, the recommended 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 likely certainly one of the key parameters to assess the transformer insulation situation; this is primarily based on the truth that DC resistance is delicate to grease 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 beneficial.
g) Inhibitor content material %
Inhibitor Content %AllRestricted to Inhibited oils,Consult oil supplier40% to 60% Of authentic value<40% of authentic value
This check is restricted to oils with this additive.
It could be advisable to contact the oil provider to verify the primary points concerning additives.
The two most common 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 significantly slows the aging process in the oil and the strong insulation.
If the result is FAIR, it’s suggested to top up the inhibitor level to the prescribed level per supplier instructions. It is advised to make use of a area professional skilled within the process to perform this activity.
If the result obtained is POOR, the advice for this situation would recommend that the top user continues to use the oil “uninhibited,” however this may result in extra speedy degradation of each the liquid and strong insulation.
It ought to be noted that some transformers have already got a built-in oil preservation system; that is designed to maintain dissolved oxygen at levels below 1000ppm. This would be in the form of a nitrogen system, a nitrogen tank or generator, or a conservator tank equipped with a rubber diaphragm (bladder). Using inhibited oils beneath these circumstances is not required, though it’d add extra protection towards oil oxidation if the preservation system ever fails. [2]
h) Passivator content
Passivator Content (mg/kg)O,A,B,C,D,E,F.>70 and steady, (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 recognized as metallic deactivators, react with reactive metal surfaces and dissolved metals corresponding to copper and silver and reduce their fee of reaction with compounds in the oil. This contains oxidation reactions with organic compounds and reactions with corrosive sulfur. Passivators are composed of two primary varieties, sulfur-based and nitrogen-based. The first suggested use of passivators in transformer oil, of which the creator 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 may deplete extra rapidly; this depletion would possibly accelerate when the oil is un-inhibited.
With GOOD outcomes, common sample intervals could be maintained.
With FAIR outcomes, preserve common monitoring.
When POOR, it is suggested to take away the oil or remove the supply of corrosivity from the oil via special oil therapy.
I) Sediment and sludge
This is not a routine take a look at.
It is suggested that this test is performed when the oil results indicate a excessive acid value and the dissipation issue is close to the unacceptable restrict.
The results have to be lower than zero.02% by mass to be negligible. If the outcomes return a value of more than 0.02% by mass, it is suggested that it be reclaimed; in any other case, an oil change is really helpful.
j) Interfacial pressure
This is not a routine test
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 aging course of. What this means in practical terms is there’s extra polar compound current in the oil, reducing the power of an oil to function an insulator in the transformer system. There is a direct correlation between interfacial tension and neutralisation quantity. Therefore, the interfacial pressure becomes a excessive quality criterion: the oil should be modified beneath a predefined restrict.
If results are GOOD, continue the common sampling interval.
If results are FAIR, lower the sampling interval.
If outcomes are POOR, examine the oil for sediment and/or sludge.
k) Corrosive sulfur
This is not a routine test.
เกจวัดแรงดันแก๊สlpgรถยนต์ is either corrosive or non-corrosive.
The presence of corrosive sulfur in transformer oil and its effect on the transformer system could be vital. The extent of the corrosion harm caused by the sulfur can be so severe that it’d trigger failure of the gear 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 merchandise utilized 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 need of corrective actions based mostly on this institute’s threat evaluation examine. [4]
l) Particle counting and sizing
Table three: Particles
Table B.1 – Typical contamination levels (particles) encountered on power transformer insulating oil as measured using IEC 60970 [5]
m) Flashpoint ° C
Not a routine take a look at
If there’s a maximum lower in flashpoints by 10%, the tools would possibly require additional inspection. This worth might differ in several countries.
It is suggested to carry out this take a look at when an uncommon odour is seen, the unit has been refilled, or an inner fault has occurred.
n) PCB (Polychlorinated Biphenyls)
This test is not to determine the situation of the transformer; it is a well being and security impact take a look at. PCB is hazardous to each people and the setting; it is important to test for PCBs after the retro fill of a transformer. It can be required each time any maintenance has been accomplished on the unit, and the potential for contamination is current. If PCB content exceeds the really helpful limits, the suitable motion must be taken.
Units with a PCB content material of more than 50ppm require a fireplace safety plan, environmental safety plan, and additional precautionary measures when upkeep is completed. This oil needs to be changed, and the oil disposed of as hazardous waste, with a certificate of secure disposal issued to the tools proprietor.
Local regulatory bodies define the bounds.
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 completely different gases and the interpretation of this knowledge in accordance with international requirements might be discussed intimately, forming part of the overall well being score willpower of the transformer.
Transformer condition monitoring is an interlaced, extremely exciting area of research. In this text, we centered on the kinds of tests 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 particular unit at a specific date and time. This makes it possible to make sure finest practice software and optimised maintenance. It additionally make it simpler to draw up a upkeep plan and action plan.
1. IEC 60422 Edition 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
three. Passivators, what they are and the way 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 16 – December 2021
Author bio:
Corné Dames is a WearCheck transformer marketing consultant. She has 20+ years’ experience within the industry, having previously worked as laboratory supervisor for a serious industrial laboratory group, focusing on transformer well being. She has been intrigued by transformer chemistry proper from the start of her profession, particularly in the evaluation of test knowledge. Corné has vast sensible and theoretical knowledge of reliability maintenance programmes.

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