Evaluation of the need for having neutral sections in Banverkets catenary system
Examensarbete för masterexamen
From the start of the electrification of the railway in Sweden Banverket has been building neutral sections in the sections point between two feeding stations. The other 16,7 Hz countries (Germany, Austria, Switzerland and Norway) does not have as many neutral sections as Sweden does. This report will evaluate the need for having neutral sections in the Swedish catenary system. To achieve the wanted 16,7 Hz and 15 kV Banverket buys power locally and then converts it in converter stations placed throughout the country. There exist two different types of converter stations, static and rotating converters. In the 1980s when the train’s weight increased the demand for higher current also increased. To handle this Banverket either had to build many new converters stations or do like Germany and build a high voltage grid. Banverket decided to build high voltage grid between Boden in the north and Häggvik and Hallsberg in the southern middle part of Sweden. The advantage with a high voltage grid is that there will not be any phase difference between two neighbouring stations. Banverket however has a problem with the power flow in this system, there are still some test with phase shifting transformers to handle this problem. Neutral sections are used as borders both for reducing the short circuit power and to use the catenary system in island mode. In the same way they are used to securely prevent that a voltage not is transferred to an overhead line that for safety reasons should be kept de-energized. They reduce the risks of creating electric arcs and the damage on section points. However they cost a lot of money to build and the heavy section isolator that are used in some cases might damage the pantograph. Neutral sections can be removed in some places, where the energizing is done from the high voltage grid or from static converters. The parts of the Swedish railway that are energized from converter stations will however still need neutral sections. The converters stations are connected with the Swedish 50 Hz grid and it does that if a fault happens in the national grid it is transferred into the catenary system. Air isolated neutral sections effect the pantographs less and will therefore cause less damage on the catenary system.
Elkraftteknik , Electric power engineering