TECHNICAL PAPER PRESENTATION

Transcription

1 1 W E L C O M E T O A C O M E T TECHNICAL PAPER PRESENTATION

2 2 POWER TRANSFORMERS - Online detection of markers for cellulose aging. BY KAI HAEMEL

3 3 A B O U T T H E A U T H O R BRIEF BIO Kai Haemel General Manager GRIDINSPECT GmbH Dipl. Ing. (graduated engineer) precision engineering and sensor technologies Professional with 15 years of experience in development and application engineering of protection devices, sensors and monitoring systems for high voltage equipment. Worked 10 years for MR/Messko as head of R&D department with responsibility for new and running products, test department and technical sales support. Together with Joerg Preusel founder of GRIDINSPECT GmbH in Main focus on application engineering of sensors and monitoring solutions for high voltage equipment including installation, commissioning and data evaluation.

4 4 O V E R V I E W & ABSTRACT SUMMARY Power transformers have to work reliable over many years. Finding the right point for exchanging it is a hard target. Taking it out too early is wasted money, taking it out too late is a high risk. This presentation should give some ideas which markers can be used to figure out aging of the isolation system. LEARN MORE

5 5 S L O W L Y A G I N G O F Y O U R T R A N S F O R M E R U N T I L I T s T O O L A T E What happens in my transformer? The oil/paper insulation system of transformers age very slowly. Over a long period of time the tensile strength gets worse until the system can not withstand the next high energy event like arcing or phase to ground failure. The component oil can be analyzed very exactly and it is easy to improve the quality when it has fallen under a defined quality level. For the component paper it looks different.

6 6 P O W E R T R A N S F O R M E R S Indicator DP value Isolation paper consists 90% of cellulose, 6-7% of hemicellulose and the rest is lignin. The cellulose molecules are long glycosechains with an oxygen binding. The length of the chain is defined with the degree of polymerization (DP) value. It describes the tensile strength of the system. New insulating paper has typically a DP value of appr Paper in a new transformer when leaving the factory appr It is considered as bad when falling below With a DP value below it is possible that it can not withstand the next arcing or fault due to the lost tensile strength.

7 7 P O W E R T R A N S F O R M E R S 3 enemies of a transformer Heat Aging rate doubles with 6-8K temperature increase. Aging rate for Kraft paper is one at 98 C hotspot temperature and for thermally upgraded paper at 110 C. Take care about your cooling system. Moisture Water is created internally due to cellulose decomposition. One water molecule results in 3 to 5 new water molecules. A very slow growing chain reaction. Water also comes from outside when e.g. having bad maintained breathers in open system or through leakages: Where oil comes out water gets in!!! Oxygen Oxygen reacts as a catalyst with other molecules to e.g. CO -> CO2. It also forces acid rising.

8 P O W E R T R A N S F O R M E R S C O M E T DP value determination State of the art are 4 methods known to determine the DP value Direct DP measurement Advantage: Exact measurement for evaluation of paper quality Disadvantage: Not practical during operation CO 2 /CO ratio Advantage: Easy measurement with DGA. Can be used for further investigations. Disadvantage: Influenced from other reactions like oil oxidation or air components. Furane (2FAL) Advantage: Relation to DP value. Can be easily done with lab analysis. Disadvantage: Low concentration especially for thermally upgraded paper. Only integrated average value, no relation to hotspot. Methanol (MeOH) Advantage: Linear relation to DP value even at the beginning of decomposition. Disadvantage: Still under investigation.

9 9 S T A T E O F T H E A R T F U T U R E Direct DP- measurement Tensile strength You need to open the transformer. Take a paper probe directly at the point where you consider the highest paper degradation usually the hot spot. In the lab the paper is cut into very small pieces and put in a special copper solution. The viscosity of this solution is an indicator for the DP value. Measurements are often not meaningful due to handling influences At the end: Very expensive and usually only done post mortem. To eliminate the handling influences it is discussed to change to a standardized method for measuring the tensile strength like done with metal, concrete or other materials. At the end: It also can t be done during operation.

10 10 S T A T E O F T H E A R T S T A T E O F T H E A R T CO 2 /CO-ratio Furan 2FAL 3 < CO 2 /CO < 10: Normal paper aging acc. to IEC60599 CO 2 /CO < 3: Mainly paper aging CO 2 /CO > 10: Overheating of paper (>160 C) or oil oxidation especially for free breathing transformers Normal aging when CO/CO 2 ratio between 1:4 to 1:6 ATTENTION: Big influence from air gases, oil oxidation and overheating of oil and paper!!! Critical level is below DP Big influence of moisture, oxygen and acid Post mortem DP investigations showed big deviations to expected DP values at hot spot.

11 11 P O W E R T R A N S F O R M E R S Markers for cellulose aging Moisture Moisture is one of the accelerators and also a chemical result for paper aging. If paper aging has increased you get rising moisture values inside the cellulose and oil. Moisture can also get in from outside. When analyzing data always take in mind that it can not be the one and only indicator. There are relations between oil moisture and cellulose moisture. Cellulose moisture above 3-4 is seen as critical. Different thresholds are available in literature. Relative moisture is easy to measure online and nearly independent from temperature. Oil ppm from Karl-Fischer in the lab is influenced from acids and alcohols and also high dependency from temperature. Oxygen If you have abnormal reactions inside the transformer the oxygen level will be reduced. Easy to measure online. Not a real indicator for cellulose aging, but take care if it comes along with CO or respectively CO 2 /CO ratio increasing.

12 12 P O W E R T R A N S F O R M E R S Markers for cellulose aging CO 2 /CO ratio Raising CO and CO2 values are markers for either paper aging or oil oxidation resp. overheating of paper. A ratio of CO 2 /CO below 3 indicates advanced paper aging CO and CO 2 are easy to measure with online DGA Check acid number if something comes from oil oxidation Furan 2FAL If something from above is abnormal a lab furan analyze should be done in a higher frequency Methanol Methanol is a marker which will be investigated in the future. At the moment no clear relation is published, but it seems to deliver a much more precise indication than 2FAL Other markers Other markers are under investigation, also markers like paper color and ε r

13 13 P A P E R A G I N G Conclusion Evaluation of paper aging There is no backwards counter for the lifetime of a transformer available on the market. Further investigations will bring more methods or algorithms to evaluate the rest lifetime. But it will never be an indication which tells you that your transformer will survive for x weeks or month. It is essential to check markers for aging and to draw the right actions. Minimizing paper aging There are several ways how you can minimize the aging even if it is in an advanced status. Sometimes it is possible to decrease the load resp. temperature. It is often possible to dry the cellulose during operation. Risk management and invest planning To optimize the conflict between reducing investment costs for exchanging equipment and minimizing the risk for unplanned outtakes it is essential to know the status of your equipment much more detailed. Further investigations New knowledges live from real field data. For universities and manufacturers of devices it is essential to work together with operators of the equipment. All the utilities and operators are invited to take part.

14 14 H O W D O W E P R O G E S S F R O M H E R E? The future of GRIDINSPECT Our company is focused to provide customers in the energy market helpful solutions. Together with our partners like Qualitrol and also the university of Hannover, Germany we work on investigations around the topic paper aging. STEP ONE GOING FORWARD STEP TWO GOING FORWARD STEP THREE Having the state of the art. Find new ways how to investigate paper aging Develop sensors for detection of paper aging Getting field experience Development of much more precise algorithms for paper aging

15 15 PAPER Q&A C O M E T C O L L A B O R A T E S H A R E K N O W L E D G E P R O G R E S S

16 16 GET IN TOUCH Kai Haemel. GRIDINSPECT GmbH General Manager +49 (0) LINKEDIN