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Delegates are invited to meet and discuss with the poster presenters in this topic directly after the session 'Storage & grid integration' taking place on Wednesday, 12 March 2014 at 16:30 -18:00. The meet-the-authors will take place in the poster area.

Bram Cloet CG Power Systems Belgium, Belgium
Bram Cloet (1) F P Pieter Jan Jordaens (2) Jama Nuri (1) Raymond Van Schevensteen (1)
(1) CG Power Systems Belgium, Mechelen, Belgium (2) OWI-lab (Sirris), Antwerpen, Belgium

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Presenter's biography

Biographies are supplied directly by presenters at EWEA 2014 and are published here unedited

Mr. Cloet has been working in the transformer industry since 2007. He is currently R&D Teamleader at the R&D Centre of Excellence for Distribution Transformers of CG Power Systems. He got his master degree in Mechanical Electrical Engineering (option electrical energy) at the KULeuven in Leuven, Belgium. After his studies he started working for Pauwels Trafo Belgium, now CG Power Systems Belgium where he worked mainly on the development and improvement of distribution transformers.


Cold start of a 5.5MVA offshore transformer


SLIM® transformers are compact liquid-immersed transformers according to IEC 60076-14, customized for typical applications such as on- and off-shore wind turbines. The state of the art SLIM® wind turbine generator transformers (WTGT) have to operate in wind farms which are often located in remote locations with harsh conditions and very low temperatures. After some days of no wind the transformer can be cooled down to -30°C or even -40°C, these conditions need to be tested in advance.


To ensure the reliability of CG Power System Belgium’s WTGT’s and the possibility to start in cold conditions several tests were conducted in OWI-Lab’s large climatic test chamber . OWI-Lab’s test facility is the first public test centre in Europe that deals with extreme climatic tests of heavy machinery applications up to more than 150 ton.

Main body of abstract

When WTGT’s have to operate in cold condition CG has to prove that the internal cooling is still working. Due to the higher viscosity at low temperature of the used cooling liquids, the natural convection cooling of the internal windings may be limited.
According to the properties of the cooling liquid that is used inside the WTGT it remains ‘liquid’ above -45°C (pour point), but due to the high viscosity the natural convection may be limited and it may be possible that the initial losses generated inside the transformers’ windings cannot be evacuated fast enough. To verify if the natural convection starts, a full load cold start test was conducted at -30°C to prove that the natural cooling of the internal windings starts immediately. During the cold start test the internal pressure and several temperatures where measured such as the top oil. Also a storage test was done at -40ºC to check if the transformer can resist this ambient temperature. This storage test was conducted to prove that no leaks or other visual issues occurred on the tank and gaskets.


These tests have proved that the WTGT can start at full load even when it has been cooled down to -30°C. The evolution of the temperature rises measured on the tank wall of the transformer didn’t show any signs of cooling problems. This test was very interesting to learn about cold start behavior of WTGT’s. There are ideas to do the test again but on a special build WTGT equipped with fiber optic temperature sensors inside the windings to be able to analyze the cooling behavior of the windings itself.

Learning objectives
• The importance of testing at extreme conditions
• How testing is done at extreme conditions
• Influence of cold temperatures on transformers
• Possible future tests giving even more insight