Extension of Innertkirchen Power Plant 1

The upgrading of Innertkirchen Power Plant 1 aims to optimise and develop the output and energy production in Innert-kirchen. The existing machinery will be upgraded with the addition of a parallel penstock pipeline and a new underground power house with a Pelton turbine.

IUB Engineering Ltd provided the following project planning services:

  • Plant design and optimisation
  • Hydraulic calculations incl. transients
  • Connection to the pressure tunnel Ø = 4.3 m, length 9'600 m
  • Upgrade of surge tank with new machine room 35 x 12 m as upper chamber
  • Steel-lined pressure shaft and horiz-ontal section, each with intenal Ø = 2.4 m, length 1 km and inclinisation/slope 70 % / 10 % (TBM excavation Ø = 3.10 m)
  • Underground power house 45 x 20 m. This cavern houses the 6-jet Pelton turbine, the generator as well as the generator transformer
  • Increase of the power from 240 MW to 390 MW
  • Throttle valve housing, connection structure
  • 2'100 m long regulated tailrace tunnel using drilling and blasting method with a cross-section of 45 m2
  • Stilling basin for the purpose of dampening hydropeaking including return structure (regulated valve and radial gate)
  • Control/regulation strategy for stilling basin and tailrace tunnel
  • Several access tunnels using drilling and blasting methods
  • Concept for access to construction site with cableway for material transport


Kraftwerke Oberhasli AG, Innertkirchen


IUB Engineering Ltd. / IM Maggia Engineering Ltd.

Construction period


Construction costs

110 mio. CHF

Scope of services

  • Construction project
  • Tendering (construction, hydromechanics)
  • Application design for construction, construction supervision and as-built drawings.