Formin power plant: with the largest Slovene reservoir
As the last in the chain of power plants on the Drava, this plant rates as the second largest in terms of electric power generated and at the same time boasts the largest reservoir in the Slovene section of the Drava River.
The power plant was completed in 1978 and due to the natural conditions, was designed as a channel-type power plant, similar to the Zlatoličje HPP. With its 29 m available head on the section between Ptuj and the national border with Croatia and with a net capacity of 116 MW, it generates 548 million kWh of electricity annually.
The damming of the Drava River with a dam in Markovci resulted in the creation of the largest Slovene artificial lake with a length of 7 km and a water surface of 3,46 km2. It is called the Ptuj Lake and it contains 17,1 million m3 of water of which 4,5 million m3 can be used for the generation of electricity. The lateral dykes are constructed on gravel and their insides are sealed with a 10 cm thick asphalt lining. Disturbances to the ground water due to leakage are prevented with drainage canals located on the outside of the dykes. The high waves that are possible in strong winds led to the construction of wave protection walls at critical spots.
The Markovci Dam has six 17 m wide spillways and is equipped with radial gates and top flaps. The dam's spilling capacity is 4200 m3/s. Above the intake of the supply channel a submerged wall has been placed that, together with the dam bridge section, prevents floating material to enter into the supply channel.
The supply channel, with a length of 8,1 km is trapezium-shaped and partly buried and partially running in a dyke raised above ground level. The bottom and inner walls are coated with a waterproof lining of asphalt and it contains seven water offtakes for the irrigation of the Ptuj Field.
The high-rise powerhouse in Formin has two overhead travelling cranes. The two Kaplan turbine units are vertical and main transformers are located to the left and right of the powerhouse. Cranes for inserting stoplogs are available at both the intake and the outlet for maintenance purposes. The intake crane also serves for cleaning the trashrack.
The discharge channel is 8,5 km long, trapezium-shaped and deeply buried. Downstream from the powerhouse, a 300 m portion of the channel is lined with concrete plates.
A 110 kV switchyard has been built on the right bank alongside the powerhouse connecting the power plant to both the Slovene and the Croation power supply system. The switchyard consists of double busbars, five line bays and two generator bays.