Photo by Linda HeronPhoto Credit

Harmon Generating Station, Mattagami River

The Lower Mattagami Project is a hydroelectric project that includes the addition of a new third generating unit to the existing two-unit Harmon Generating Station.

Existing Facility

The existing Harmon facility includes two vertical propeller turbine-generator sets, penstocks and draft tubes, and three existing single-phase transformers. Harmon has been in-service since the mid-1960’s.

Located 90 km north of Kapuskasing, Ontario, the facility is operated remotely from OPG’s Northeast Control Centre located at the Porcupine Transformer Station in Timmins, Ontario.


The expansion includes one vertical propeller turbine-generator set, penstocks and draft tubes, and one new three-phase transformer. The addition of the new generating unit adds 78.3 MW to the existing capacity for a total site capacity of 219.3 MW at a head of 31.1 metres.

As part of the expansion, a tailrace gate hoisting system is installed on the existing powerhouse tailrace deck, extending over the new tailrace deck of the powerhouse extension.

Water from the Mattagami River is conveyed from the existing Harmon GS intake structure for the third generator unit to the new spiral case via a concrete encased steel penstock.

The new generating unit is installed at the existing concrete structure. All three generating units share the same gravity dam and powerhouse.

The new generating unit is connected to Hydro One’s 230kV L20D circuit.

Location: Harmon Township, Ontario
River System: Mattagami River
Nameplate Capacity: 219.3 MW
OPA Contracted Capacity: 219.3 MW
Operator: Ontario Power Generation
Technology: Hydroelectric
Turbines: Three vertical propeller turbines
Originally Built: Mid-1960’s
Coordinate: 50° 06’ 43” N, 82° 12’ 30” W


Project Progress (December 31, 2013)

  • Installation of new intake gate completed
  • Marine pad and spillway bridge removed
  • Operational testing to start in Q1 2014



Ontario Power Generation Inc.