response to a fire alarm or a power failure automatically close the doors. Ventilation of the generator floor was further enhanced in 2002 by installing a ducted fan to import cool air from a dam drainage gallery. Interconnecting transformer In 2012 the original 50 MVA 220/110 kV interconnecting transformer T10 was replaced with a new 150 MVA unit which removed a significant restriction on operating of the Southland 110 kV network. This also removed the station's previous restriction of the 110 kV generation to 90 MW and hence the total station output to 290 MW. Design The power station consists of an , concrete gravity dam from which eight steel penstocks supply water to a powerhouse containing the turbines. The penstocks change from an intake section to 18 ft in diameter before tapering to 15 ft (1.4 m) where they enter the scroll case. Three 135 ton (137 tonne) spillway gates supplied by Sir William Arrol & Co. are located on the West (right) side of the dam. The designers anticipated a 500-year flood of . As a result, the spillway was designed with a capacity of . At the base of the spillway were three 80 ton (81.3 tonne) low-level sluice gates supplied by Stahlbau of Reinhausen in Germany designed to pass . During construction these sluice gates were used to divert the river via a diversion channel. The upstream section of the diversion channel was unlined and followed an old natural channel of the river before reaching the spillway and sluice gate block which is curved at the exit to direct water away from the outdoor switchyard. The surfaces were finished to a high standard to ensure a smooth flow of the water during medium and high flows. One sluice gate was subsequently plugged with concrete leaving only sluice gates No. 2 and No. 3 in service. Powerhouse The superstructure of the powerhouse is constructed of welded steel framed clad in precast concrete panels. Two 118 ton (120 tonne) overhead cranes manufactured by Sir William Arrol & Co run over the full length of the powerhouse, including the unloading bay. The main generating equipment arranged on three floors: the main floor at , the generator floor at , and the turbine floor at with cable galleries on the downstream side that run the length of the building. The choice of the level of the main floor was governed