News / 1.9.2015

New underground substation to open in expanding Pasila

A new underground substation will be inaugurated in Ilmalantori. The substation will strengthen electricity distribution in the nearby areas and improve the security of electricity supply.

The Pasila region is growing rapidly, and construction will continue in the forthcoming years. Further construction and the growing number of residents also require increased substation capacity. In order to save valuable urban space, the new substation has been built into an underground cavern at a depth of 30 metres. Helen Oy’s district cooling storage facility is also located in the same network of tunnels beneath Pasila.

– Underground construction differs slightly from ordinary construction, explains project manager Tero Pietikäinen of Helen Sähköverkko Oy. – The long but narrow substation at Ilmalantori has been built into an elongated network of caverns. The facility was built into its rooftop height in three stages, starting from the back of the cave.

At the Ilmalantori substation, excess heat coming from the main transformers is utilised in the heating of the substation premises. The substation uses earth-fault current compensation equipment, which improves the security of supply in the electricity network and minimises power cuts.

Helen Sähköverkko has a total of 23 substations throughout Helsinki. The Ilmalantori substation is the fourth one to be built underground. The other underground substations are located in Punavuori, Kamppi and Kluuvi. The Meilahti and Vallila substations also utilise underground facilities. The next new substation will be built in Kalasatama, and its construction work will start in spring 2016.


  • The size of the cavern facility excavated at the Ilmalantori substation: 
  • length 132 m x width 15 m x height 13.5 m
  • The excavation of the cavern facility was completed in 2010
  • The substation base is 32 metres below Ilmalankatu
  • The total length of the substation is 70 metres
  • A total of some 33 kilometres of cabling was laid in the construction stage
  • The construction of the substation was launched in 2013, and the new station will be inaugurated in September 2015
  • Helen Sähköverkko has a total of 23 substations in Helsinki.

 Ilmalantori substation