Reactive power compensation
Due to the 150-kV underground cabling, the network in the city of Zurich can potentially manifest capacitive behaviour (as seen by the 220-kV network) during “low-load” conditions. This causes voltage increases and can lead to voltage violations. As part of the network expansion plan, the local distribution grid operator (ewz) is planning, jointly with the utility Axpo, the Swiss Federal Railways SBB and the transmission system operator swissgrid, the renovation and construction of power lines in the south of Zurich. In particular, it is planned to change the southern infeed from the 150 kV substations in Obfelden and Samstagen to the 220 kV substation in Waldegg. In this context, a 8.3 km long cable between Waldegg and Frohalp is planned at the 220-kV voltage level. Since voltages exceeding 247 kV were measured at the substations during off-peak times, each additional meter of cable would make reactive power compensation necessary. The study addresses the following points.
- In terms of network planning variants (one/two cables through Uetlibergtunnel or single line/cable between Thalwil and Wollishofen substations), the rating and location of the reactive power compensation necessary to keep the voltages within the permissible limits should be determined.
- Determination of system losses for both planning variants with and without reactive power compensation, depending on the rating and location of the latter.