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1University of Missouri, United States of America; 2SEA MARCONI TECHNOLOGIES S.a.s.; 3University of Roma "La Sapienza"
Natural esters (triglycerides) possess desirable attributes such as the higher fire points and better environmental compatibility relative to petroleum-derived insulating mineral oil, as a result, the use of such natural esters is on the rise as insulating and heat transfer fluids in electrical devices such as transformers. However, natural esters differ significantly in chemical composition from mineral oils and are more prone to oxidation than mineral oils. High susceptibility of natural esters can be addressed in part through the use of natural esters with higher monounsaturated fatty acid-high oleic natural esters. Recently several high oleic acid soybeans have been introduced commercially. These include Plenish® (Pioneer / Dupont) Vistive Gold® (Monsanto / Bayer) and Soyleic® (Missouri Soybean Association). Both Plenish® and Vistive Gold® are obtained from GMO soybeans, while Soyleic® has been developed through more traditional plant breeding. The oleic acid content of the three natural esters was found to be 79%, 71%, and 81% respectively. While polyunsaturated fatty acid (linoleic and linolenic) contents of the three natural esters were found to be 10.3%, 22.5%, and 7.8% respectively. High oleic soybean oils along with canola oil with oleic content of 75% and polyunsaturated fatty acid content of 17.2% and generic soybean with oleic content of 24.5% and polyunsaturated fatty acid content of 60.0% were subjected to accelerated aging under conditions outlined in IEC 62770 2013. Test results showed that natural esters with higher oleic and lower polyunsaturated acid contents were more stable than the natural esters with lower oleic and higher polyunsaturated content. This stability was reflected in little or no increase in kinematic viscosity and little increase in dissolved acidity. These natural esters are therefore more suitable for dielectric applications where long-term stability is of paramount concern.
ID: 1135 / S3: 2
Increasead Lodability of Transformers Immersed in Natural Esters
Fabio Scatiggio, Francesco Maria Pepe, Simone Sacco, Claudio Angelo Serafino
TERNA RETE ITALIA, Italy
Mineral-base oil has been the main insulating liquid for filling power transformers since the 1900’s due to its ready worldwide availability, low cost and good properties. Anyway, in recent times the new desires for a safer nonflammable, an environmental acceptable and a less impacting on sustainable common resources fluid has driven many users in the research and use of alternative fluids to mineral oil. Despite the availability of other fluids, the synthetic and natural (from vegetable seeds) esters (NE) represent the major alternative to mineral insulating oils. Terna as Italian Transmission System Operator (TSO) in according to European Union Directive 2001/42/EC should aim at guaranteeing high levels of environmental protection and safety, so Terna is also aware of its responsibility towards the community and has translated this into a single strategy: to find the right balance between the country's energy needs, nature conservation and the safeguarding of Italy's cultural heritage. In addition to the environmental and fire safety benefits, the review of the possible advantages of natural ester-filled transformers allowed identifying alternative design criteria with relevant financial benefits. The TERNA goal was to increase the loading ability of their transformers, mainly by enhancing a much higher limit for overloading in comparison to traditional transformers. For this prototype TERNA selected a 400/135 kV 250 MVA autotransformer, a standard practice for their network. To explore the superior thermal class of the new insulation system, the transformer manufacturer confirmed the possibility of designing this transformer with a “permanent additional capacity”. Five autotransformers with NE are already in service and in its next-2-years strategic plan Terna has planned the installation of more than 20 new power autotransformers filled with natural ester
ID: 1318 / S3: 3
Experience of Synthetic Ester Filled Transformers in SP Energy Networks
ShengJi Tee, David Walker, Malcolm Bebbington
SP Energy Networks, United Kingdom
A fire in an embedded substation triggered a policy change in SP Energy Networks (SPEN) which led to the use of synthetic ester filled transformers in 11kV distribution embedded substations. Driven by improved understanding from research and increased experience in operating synthetic ester filled transformers, the use of synthetic ester then expanded to 33kV primary and 132kV grid transformers. This paper charts the increased use of synthetic ester filled transformers in SPEN along with sharing the benefits realised from adopting synthetic ester applications. Factory acceptance test and condition monitoring data are also presented which indicated the suitability of synthetic ester filled transformers as viable alternatives to conventional mineral oil filled units.
ID: 1334 / S3: 4
Natural ester liquid-filled transformers power the Olympic Games
Kevin James Rapp1, Revin Wang2, Alan Sbravati1, Roberto Ignacio3, Vander Tumiatti4, Massimo Pompili5
1Cargill, Plymouth, MN United States of America; 2Cargill China; 3Cargill Brazil; 4Sea Marconi, Turin, Italy; 5University of Roma-Sapienza
This paper will present natural ester transformer operating data with liquid test results from the units since installation. Various facts and experiences from transformers of two Olympic cities will be shared. The results of physicalchemical and electrical testing including dissolved gas analysis will provide the performance history in the field of a group of power transformers of 138 kV design and of unique designed submersible 10 kV distribution units filled with natural ester fluid, some in service for more than 4 years.
ID: 1307 / S3: 5
Investigation of the Total Flow Rates in Oil Natural Transformer Retrofilling Scenarios
Xiang Zhang1, Zhongdong Wang1, Qiang Liu1, Attila Gyore2, Kevin Rapp3
1The University of Manchester, United Kingdom; 2M&I Materials; 3Cargill Bioindustrial- Global Dielectric Fluids Technology
Retrofilling transformers with a new liquid has been considered as an option for life extension and/or uprating purposes. The determination of the new total liquid flow rate is of vital importance in assessing the effect of retrofilling on flow and temperature distributions in the winding, especially for ON transformers. This paper presents the determination of flow rate ratios for four liquids—a mineral oil, a GTL oil, a synthetic ester and a natural ester—in ON transformer retrofilling scenarios. Flow rate ratios among different liquids are provided for a simplified condition of linear radiator oil temperature variation. For a more realistic exponential radiator oil temperature variation, the detailed transformer geometric information is needed to estimate the total flow rate. In addition, a hydraulic winding network model is established to prove that “minor pressure losses” due to change of flow directions is indeed minor for ON transformer liquid flow conditions, justifying neglecting the minor losses in the deduction of the total liquid flow rate.
ID: 1358 / S3: 6
Fire simulation tests of mineral oil and natural esters transformers
Michele Mazzaro1, Domenico De Bartolomeo1, Luigi Calcara2, Massimo Pompili2, Fabio Scatiggio3, Andrea Valant3, Massimo Rebolini3, Elisabetta Bemporad4, Alessandro Ledda4, Flavio Mauri5, Mauro Salvadori5, Alfonso Sturchio5, Marco Falconi6, Antonella Vecchio6
1Italian Ministry of Home Affairs National Fire and Rescue Service Dept., Italy; 2University of Roma "La Sapienza", Italy; 3Terna Rete Italia, Italy; 4Italian National Institute for Insurance against Accidents at Work (INAIL), Italy; 5e-distribuzione, Italy; 6ISPRA Dept. for Geological Survey of Italy
This paper describes the work carried out by the Italian Institutional Working Group on Natural Esters; this Group has been promoted by the University of Roma "La Sapienza", the National Firefighters Authority, the National Institute for Insurance against Accidents at Work (INAIL) and the Department for Geological Survey of Italy (ISPRA) with the objective of further validating the real possibility of risk mitigation for humans and environment through a more widespread use of a new generation of transformers insulated with natural ester liquids. A useful contribution to the activities of the Italian Institutional Group on Natural Esters has been also given by the participation of some of the major players in the electrical sector, such as: Italian TSO, main Distributors, Natural Ester producers and transformer manufacturers. The development of this Italian Group at international level has been the set-up of the CIGRE WG D1.68 “Natural and synthetic esters – Evaluation of the performance under fire and the impact on environment”, which is actually preparing a report on this subject. The present paper reports the main results of experimental comparative fire simulations of both mineral oil and natural esters distribution transformers.