by Brenna ShumbamhiniJune 9, 2022
Corne Dames
Condition monitoring is the frequent collecting, measuring, recording, and evaluation of the related information relating to an asset’s operation. If we interpret the information correctly, it can provide us nice insight into the asset’s condition.
Frequent monitoring of the asset may find yourself in less upkeep required or more extended durations without any maintenance required.
It is essential to identify the key parameters that are wanted to give us a whole image of the particular status of the transformer and the motion we have to take to make sure the continued reliability of the asset to achieve the utmost lifetime.
What is the information telling us?
Has the condition of the unit modified for the rationale that last upkeep period?
Is it safe 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 long can we use the unit before we need to think about replacement?
Are the recognized problems of a recurring nature?
Effective situation monitoring outline
It is vitally important to identify clear targets as a part of your strategy. What do you want to achieve by implementing this situation monitoring plan? Is it in-service failure prevention? Or possibly life extension? Maintenance deferral? By stipulating the finish result and what you wish to accomplish, it would be much easier to identify the required parameters.
Health indexing of assets 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 entire worth 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 crucial values stipulated within the varied standards.
The scope of oil evaluation, interpretation of the info, and important values
At the start of this part, it is important to state that we deal with completely different size transformers in the industry. Transformers are divided into classes according to the kV rankings of the equipment. It is up to the reliability or asset manager to make use of the rules for bigger tools, thereby implementing shorter increment oil analysis and electrical tests.
The maintenance engineer or manager needs to determine what kind of testing would benefit him in identifying downside areas within his fleet. Some of the analysis has been identified as to routine kind exams. Still, there might be an extensive range of tests that may assist in identifying specific drawback criteria within the system, which could not be clear through the everyday day-to-day analysis often performed.
Please see the rating classes in TABLE 1
TABLE 2 explains which oil analyses are recommended and how usually or beneath which circumstances.
Oil sampling
The taking of the oil pattern is likely one of the most crucial and significant influencers in the evaluation end result. If a sample is not taken to the prescribed procedure, then there’s a vital chance that the evaluation carried out, and the outcomes acquired, are of no use.
Care must be taken to ensure quality management procedures are applied in each step of the sampling course of as set out by worldwide standards. A good quality sample taken by applying the correct procedure is important. A sample may be contaminated by numerous factors, all of which might influence the outcome of the leads to a unfavorable method.
All steps involved in sample taking must adhere to quality management procedures, including the container that is used, the sampling package, the taking of the pattern, the marking of the sample, the closing of the pattern, the storage and handling of the sample, and then the delivery of the sample to the laboratory.
If the sample identification and pattern knowledge are handwritten, the human issue can result in 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 accomplished in neat, easy-to-read handwriting. The label must be waterproof, and the pen used to put in writing on the label ought to be oil- and water-resistant. Otherwise, some information could be misplaced, making it extraordinarily tough for the laboratory personnel to complete the report or allocate the sample to a specific transformer.
Now, let’s talk about the kinds of checks to discover out the transformer’s condition, the crucial values, and the really helpful actions in every 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 many “tests” is a visible inspection of the oil pattern in a transparent vessel to discover out the colour, turbidity, and attainable particle identification.
Dark oils might point out chemical degradation or contamination of the oil.
When there may be lots of turbidity, it would point out a high water content within the oil.
If the drain valve was not cleaned by the sampler, the dirt particles in the drain valve may be integrated into the pattern. If particles are recognized as carbon, it might point out a potential electrical fault within the unit. The DGA evaluation of the oil will confirm if so.
Clear oils without contamination will point out a great situation, and no action is really helpful.
When oils are dark or turbid, additional evaluation will confirm any problems. The oil evaluation results may also determine the diploma and sort 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 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 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 avoid flashover in the unit, the breakdown voltage should be high.
If the values are Good, it is recommended to proceed with the present pattern interval motion plan.
If the values are Fair, more frequent sampling is recommended in collaboration with different parameter outcomes just like the water content, DDF (dielectric dissipation factor), and acidity.
If values are Poor – it is strongly recommended to recondition the oil by way of oil reconditioning processes. If alternative checks indicate extreme growing older, the oil could be changed with new or reclaimed oil. Another choice would be to carry out 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 well as some other compounds. Another benefit is that the oil can be re-used, and in most conditions, this might be done without switching off the unit, which contributes to cost-saving. If in doubt – instead switch off the unit throughout this treatment process.
If the values are Poor, it’s advisable to take action as soon as attainable and not delay the upkeep course of. Excess water in the transformer system decreases the projected transformer lifetime considerably; extraordinarily high water content 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 check
This is a routine test for all courses of electrical tools, except class G
The outcomes of this check should all the time be thought of at the aspect of the breakdown strength. If it’s discovered that the water content is high and the breakdown strength is low, additional motion needs to be taken. It is beneficial that a second pattern from the same unit is tested to substantiate the outcomes.
In the case of switching gear, the place there is no paper present, the breakdown voltage is the determining factor.
It ought to be noted that the bounds indicated by IEC 60422 Edition 4 apply to transformers with working temperatures between 40 and 70 °C. If it’s discovered that the unit’s working temperature is exterior this temperature range, it is best to discuss with Annex A of the usual.
When the value obtained through analyses is GOOD, the normal sampling interval could be maintained, requiring no further motion.
When the value returns a FAIR outcome, extra frequent sampling is beneficial. It can be useful to contemplate different parameters like the breakdown voltage, particle content and DDF/resistivity, and acidity to determine on the motion to be implemented.
A POOR end result will require quick action from the asset manager. This might include taking another sample to substantiate the outcomes from the first evaluation. If it is confirmed that the water content material is high, the oil could be filtered; this course of should take away a large portion of the moisture from the oil if applied correctly. Follow-up samples need to be taken to guarantee that the moisture content continues to be throughout the required limits. The reason is that probably the most good portion of the water is caught up within the paper system in the transformer. เกจวัดแรงดันลมดิจิตอล will transfer from the paper into the oil underneath conditions that favour this movement. It could be discovered later that the oil within the water has elevated again with none obvious purpose, but the source would be the paper within the transformer.
A visual inspection can be recommended to discover out if any water may move into the transformer or electrical tools via leaks. This problem could be more severe if the transformer or electrical gear is exterior and never in a covered space.
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< hundred.15 to zero.30>0.30
F, G Not a routine take a look at
This is a routine test for all lessons except 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 help within the formation of the acids. Because acids are polar compounds, it’ll adversely have an result on the insulation properties of the oil and will enhance paper degradation. If left untreated in transformers, this will result in sludge formation, often around the decrease components of the transformer core. The sludge will ultimately form a semi-solid substance that is extraordinarily tough to remove.
If the result is GOOD, the regular sampling interval can continue.
In case of a FAIR result, the sampling interval must be decreased to fit the situation. Future evaluation ought to embrace 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 decide to reclaim the oil or substitute it with new or reclaimed oil, whichever possibility would possibly swimsuit their requirements one of the best.
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 zero.20>0.20
B, C<0.a hundred.10 to zero.50>0.50
D<0.010.01 to zero.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 check for all lessons of electrical equipment, besides F and G
The dielectric dissipation issue or tan delta of this take a look at provides data 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 phase displacement and dielectric losses. Other impurities that might affect the dissipation issue include water, dissolved insulating resin, and paper.
When the result’s FAIR, extra frequent sampling and checking extra parameters is recommended.
When the result is POOR, reclamation or an oil change is beneficial. The construction of the oil is broken, 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 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 test
DC resistivity of the oil is amongst the key parameters to assess the transformer insulation condition; that is based mostly on the truth that DC resistance is sensitive to oil degradation.
When the result’s FAIR, more frequent sampling and checking further parameters is recommended.
When the result’s POOR, reclamation or an oil change is really helpful.
g) Inhibitor content percent
Inhibitor Content %AllRestricted to Inhibited oils,Consult oil supplier40% to 60% Of unique value<40% of original worth
This test is restricted to oils with this additive.
It could be advisable to contact the oil provider to verify the details concerning additives.
The two most typical oxidation inhibitors for transformer oils are 2,6-di-tertiary-butyl para-cresol (DBPC) and 2,6-di-tertiary butyl-phenol (DBP). The purpose of the inhibitor is to stop oxygen from reacting with the oil. This considerably slows the aging process within the oil and the solid insulation.
If the result’s FAIR, it’s advised to high up the inhibitor level to the prescribed level per provider instructions. It is suggested to make use of a area professional educated within the procedure to perform this process.
If the outcome obtained is POOR, the advice for this state of affairs would recommend that the top person continues to make use of the oil “uninhibited,” but this may result in extra rapid degradation of both the liquid and stable insulation.
It ought to be famous that some transformers already have a built-in oil preservation system; that is designed to keep dissolved oxygen at ranges under 1000ppm. This can 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 isn’t required, although it’d add additional protection in opposition to 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 steady, (rate of lower < 10/mg/kg/year)50-70mg/kg or<70mg/kg, with a significantrate of lower of >10mg/kg/year<50 and reducing at >10mg/kg/year
Passivators, also identified as metal deactivators, react with reactive metallic surfaces and dissolved metals corresponding to copper and silver and reduce their price of reaction with compounds within the oil. This contains oxidation reactions with organic compounds and reactions with corrosive sulfur. Passivators are composed of two fundamental types, sulfur-based and nitrogen-based. The first suggested use of passivators in transformer oil, of which the author 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 extra quickly; this depletion might accelerate when the oil is un-inhibited.
With GOOD results, regular pattern intervals may be maintained.
With FAIR results, keep common monitoring.
When POOR, it is advised to take away the oil or remove the supply of corrosivity from the oil via special oil treatment.
I) Sediment and sludge
This is not a routine test.
It is advised that this check is performed when the oil outcomes indicate a high acid value and the dissipation issue is near the unacceptable restrict.
The results must be less than zero.02% by mass to be negligible. If the outcomes return a price of more than 0.02% by mass, it is advised that it’s reclaimed; otherwise, an oil change is beneficial.
j) Interfacial rigidity
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 take a look at
F, GNot Applicable
The interfacial rigidity between transformer oil and water reduces through the growing older process. What this implies in practical terms is there’s more polar compound present in the oil, decreasing the power of an oil to function an insulator in the transformer system. There is a direct correlation between interfacial rigidity and neutralisation number. Therefore, the interfacial tension becomes a high quality criterion: the oil should be modified beneath a predefined restrict.
If outcomes are GOOD, continue the regular sampling interval.
If outcomes are FAIR, lower the sampling interval.
If results are POOR, check the oil for sediment and/or sludge.
k) Corrosive sulfur
This isn’t a routine take a look at.
Oil is both corrosive or non-corrosive.
The presence of corrosive sulfur in transformer oil and its effect on the transformer system may be vital. The extent of the corrosion injury attributable to the sulfur could be so extreme that it’d cause failure of the equipment if not checked. The addition of a copper passivator can scale back the impact of this compound on the transformer system.
In a examine by Doble, it has been discovered 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 need of corrective actions based mostly on this institute’s threat assessment examine. [4]
l) Particle counting and sizing
Table three: 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 test
If there’s a maximum lower in flashpoints by 10%, the equipment may require additional inspection. This value might differ in numerous countries.
It is suggested to carry out this take a look at when an uncommon odour is noticed, the unit has been refilled, or an inside fault has occurred.
n) PCB (Polychlorinated Biphenyls)
This check is to not 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 surroundings; it’s critical 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 potential of contamination is current. If PCB content exceeds the beneficial limits, the suitable motion needs to be taken.
Units with a PCB content material of greater than 50ppm require a fireplace safety plan, environmental safety plan, and extra precautionary measures when upkeep is done. This oil needs to be changed, and the oil disposed of as hazardous waste, with a certificate of secure disposal issued to the equipment proprietor.
Local regulatory our bodies outline the limits.
o) DGA (Dissolved Gas Analysis)
As DGA is an intricate science with plenty of information and interpretation, we will talk about this phenomenon partially II of the article. The limits for the totally different gases and the interpretation of this information in accordance with worldwide requirements will be discussed in detail, forming part of the general health ranking dedication of the transformer.
Transformer situation monitoring is an interlaced, extremely thrilling field of study. In this text, we targeted on the types of checks to discover out the situation of the transformer, the important values, and the beneficial actions.
The Health Index indication makes it possible to see the supposed reliability of a particular unit at a selected date and time. This makes it attainable to make sure greatest practice software and optimised upkeep. It also 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 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.
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 printed by Transformer Technology Magazine Issue sixteen – December 2021
Author bio:
Corné Dames is a WearCheck transformer advisor. She has 20+ years’ expertise in the industry, having beforehand worked as laboratory manager for a major industrial laboratory group, focusing on transformer health. pressure gauge หน้าปัด 2 นิ้ว has been intrigued by transformer chemistry right from the start of her profession, notably in the analysis of take a look at information. Corné has huge practical and theoretical information of reliability upkeep programmes.

Leave a Comment