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Switching Installation

The switching facility is an electrical installation that makes the reception or sending of electrical energy possible. Due to the gradual construction of the units at the Šoštanj thermal plant, the high tension outlets on individual units are adapted to the transmission network.

Units one, two and three send their energy output into the system at 110kV, via two-system switchgear. The switching installations are enclosed and insulated by the SF6 insulating gas (sulphur hexafluoride) with a pressure of 6.1 bars on the circuit breakers and 3.8 bar in the rest of the installation. The nominal data for this switch is: Un=123 kV, In=2kA, Ik3=31kA, Iu=80 kA. It is the SF6 gas that allows for a fourfold reduction of the switch facility operating surface compared to an open-air version. The facility is controlled by a computer system with the possibility of remote switching of the transmission lines from the Maribor regional control centre. The switching facility has 15 lines, three for generators 1-3, a connective line, five transmission lines, five lines for the general-purpose transformers and a monitoring line.

Generating unit four outputs its energy into the 220kV grid through a switching facility, which is also insulated with the SF6 gas, but is an open-air version. The old facility was completely replaced in 2002. The gas pressure on the circuit breakers is at 0.78 bars. The nominal data for the facility is Un=245kV, In=1,25kA, Ik3=40kA, Iu=100kA.

Generating unit five, which sends its output to the 400kV grid, is also connected to the transmission line by a SF6 gas insulated switch; this one replaced its predecessor in 2001. The gas pressure on the circuit breakers is at 0.69 bar, Un=400kV, In=2kA, Ik3=40kA, IU=100kA*. The gen. unit four and five switches control system is integrated in the functional management group for the turbines during the start-up of the units, shutdown can be instructed manually or can be activated by safety mechanisms.