Wanjii power station is situated in Murang’a County  80km from Nairobi. This is a run-of-river plant with a small sized dam having low water storage capacity. It has Mathioya dam on Mathioya River and Maragua dam on Maragua River. The source for the two rivers is the Aberdare forest. The station has a total capacity of 7.4MW. Units 1 & 2 are each rated at 2.7MW and they get their water from Mathioya River through a tunnel that is 5.2km long and runs under Murang’a town. The water from these machines flows into Maragua River. Units 3 & 4 are served by Maragua River. A project to modernize and upgrade the units has already been awarded to Voith Hydro, Germany. Site installation works are planned to start in June 2019.

Units 1 & 2 (Merilla units)
Year of commissioning: 1952
Installed capacity: 2 x 2.7MW
Turbine type: Horizontal Francis
Turbine manufacturer: Harland, UK
Design head:  {51.2m – 1 Machine; 40.5m – 2 Machines}
Design speed: 333rpm
Runner type: Vertical Francis runner

Generator manufacturer: UCM Hydro Romania
Generator rating: 9100kVA
Generator voltage: 11000V
Generator current: 478A
Rated power: 7735kW
Frequency: 50Hz
Power factor: 0.85

Excitation voltage: 130V
Excitation current: 520A
Excitation system: Brushes

Units 03 and 04 (Maragwa units)
Year of commissioning: 1954 units
Installed capacity: 2 x 1.0MW
Turbine type: Horizontal Francis
Turbine manufacture: Harland, UK
Design head: 68.2m
Design speed: 500rpm
Runner type: Vertical Francis runner

Generator manufacturer: UCM Hydro Romania
Rating: 6070kVA
Rated voltage: 11000V
Rated power: 5159kW
Frequency: 50Hz
Power factor: 0.85

Exciter Voltage: 85V
Exciter current: 550A
Excitation System: Brushes
Protection degrees: IP44