Availability of different transmission systems for long distance transmission

摘要

In the next ten years the power generation from renewables in Germany will increase to 25 up to 30 %. Thelargest portion will be produced by offshore wind energy generation far away from the load centres. Caused bythe changed generation and by additional horizontal loadings of the EHV (Extra High Voltage) grid due to aconsiderable increase of trading activities strong transmission routes from the northern to the southern part inGermany have to be provided.The extension of the existing EHV grid on the 220 kV and 380 kV level presumably cannot avoid contingencies,since this grid will reach its capacity limits and due to the extensive loading stability problems cannot beexcluded. Therefore an overlay grid is under discussion at which different technical solutions, e. g. 750 kV ACtransmission, ± 500 kV DC transmission, are considered.A very important planning criterion is the availability of the transmission systems installed. It gives informationwhich redundancy is necessary in the overlay grid, but also in the subordinate underlayed grids. For this, thetransmission systems are subdivided in the different components. The most complex system, the DC connection,comprises AC switchyard with filters, converter transformer, converters, control and protection, auxiliarydevices, DC switchyard with filters, DC lines consisting of towers, conductors and insulators. The 750 kV ACconnection is subdivided in the same way: AC switchyard, AC lines consisting of towers, conductors andinsulatorsThe investigations regarding unavailabilty reflect the failure rates and the outage time for repair, replacing andputting into service. The failure rates and outage time are derived from own service experience or reference ismade to different CIGRE data. The overall unavailability of the system in question is determined by logicallinking of the unavailabilty of the various components. Finally the unavailability of the 500 kV DC connection iscompared to that of the 750 kV AC connection and to a system based on meshed or serious compensated 380 kVtransmission lines.The results indicating that the two solutions feature a comparable unavalaibilty are an important input for thedecision making process with regard to the future grid extension.