Gas turbine units PB 1-3

Three gas blocks from the producer AEG Kanis started operating in 1975. At the time of construction, the exhaust system had built-in utilisers - boilers for waste heat of exhaust gases. They produced steam for two steam turbines and thus replaced coal boilers. This facility was the first combined gas-steam process in former Yugoslavia. Due to wear and tear and a small number of operating hours of the steam part of the plant, the utilisers were removed in 2012. From then on, the PB 1-3 gas blocks have been operating in a simple process.
The blocks were originally equipped for the use of liquid propellants and in the mid-1990s the PB 2 and PB 3 gas blocks were upgraded with the possibility of using natural gas.
The gas blocks are characterized by an extremely reliable construction and a quick start-up, because they need less than 15 minutes to achieve rated power. For start-up, each gas turbine is equipped with a diesel engine which allows start-up from a de-energised state ("black start") and island operation. In the event of a breakdown of the power system, any of the PB 1-3 gas blocks can be used to start the PB 4 and PB 5 gas blocks. In this way a start-up of all of the gas blocks of the power plant is possible without the power supply from the network.
After the construction of the Krško Nuclear Power Plant, the PB 1-3 gas blocks, with the capacity to start from a de-energised state, have become one of the independent external power sources, which enables a safe shutdown of Krško in the event of a breakdown of the power system.
Gas blocks are of batch version and consist of the following main packages. 


Command package
It contains electronic systems for gas turbine control and systems for the supply of auxiliary drives. Particularly important are the systems for the start-up and shutdown control, for speed control, for the regulation of the load on the gas block, and the protective systems.
Turbine Package
The turbine package consists of a compressor, a combustion chamber, a gas turbine and auxiliary drives, which include a diesel engine to start the turbine, an auxiliary reducer, fuel pumps, lubricating oil and cooling water pumps, and other auxiliary mechanical systems necessary for the operation of the block.
Generator package
The generator package consists of a reducer, which adjusts the rated turbine rotation speed (5120 min^-1) to the rated generator rotation speed (3000 min^-1), and a generator. The generator converts the mechanical work of the turbine into electricity and is connected via a generator circuit breaker to a block transformer and to a transformer for its own use of the block.
The generator voltage is transformed to a 110 kV voltage level via a block transformer (10.5 kV/110kV-28 MVA) and is transmitted via a 110 kV GIS to the Slovenian electric power system.