ELECTRIC POWER

Waikato Times, Volume 129, Issue 21583, 20 November 1941, Page 6

ELECTRIC POWER

PLANT FOR KARAPIRO HUGE UNITS TO BE INSTALLED TURBINES OF NEW TYPE WELLINGTON, Wednesday The three 42,000 horse-power turbines on order for the Karapiro hydro-electric station are of a type not generally known in New Zealand. They are the recently-developed “Kaplan” type, in which the blades of the water-wheel are varied in pitch to suit the amount of power that is being generated. They are thus analagous to the modern aircraft airscrew, of which the blades are varied in pitch to obtain highest efficiency at different air speeds and engine power. One works in air, the otner in water; the aims and ends are the same, though the constant speed airscrew and the Kaplan type turbine were arrived at by aeronautical and power engineers working independently in search of higher efficiencies under varying load conditions. Precision and Weight In the water turbine the speed of the rotor will be constant, but by varying the pitch of the blades the efficiency can be kept very high over a wide range of loads, and thereby the maximum amount of electricity can be generated from the water available. It is not a matter of jet adjustment alone; the blades of the water wheel are altered automatically in conformity with changes in load. Each of the live stainless steel blades of the turbines weighs about 2{ tons. Stainless steel is used to prevent corrosion, a serious trouble in turbines unless special precautions are taken against it.

The 30,000 k.v.a. generators are coupled directly to the turbines below by a vertical shaft and will generate power at 11,000 volts. The total weight of each unit will be 621 tons, the turbine weighing 282 tons and the generator 329 tons. The overall diameter will be 32 feet and the total height of each unit will be over 50 feet.

To house these great machines, auxiliary generating units, switch gear and controls, workshops, offices, test rooms, stores, etc., the powerhouse, in reinforced concrete, will be 260 feet long, 95 feet wide, and over 100 feet from foundations to roof. Two 100-ton cranes will travel the length of the building to handle the great weights of sections of turbines and generators. Waikato Developments

The power in water flow may be used and used again, given sufficient fall form one development to another. At Waikaremoana the water from the lake may ultimately be used three times over, and plans for Waikato hydro developments are for several stations spaced down from the river from Taupo. Horahora was the first Waikato scheme; Arapuni was the second; Karapiro is the third, but when Karapiro is developed the small Horahora station will be dismantled and removed, for the site will be submerged by the new lake. Surveys at Karapiro began some years ago and preliminary exacuation and construction about 18 months ago. Steady progress has been made by the Public Works Department during the past year. Arapuni and Karapiro Excavation work on both sides of the river is preparing for the placing of the concrete abutments of the dam, cast into the solid rock of the country. The dam will be mass concrete, 170 feet high from foundations to crest —more than one and a half times the height of any Wel--1 i’gton building—and about 1000 feet long. It will be a combined gravity and arch type. The Arapuni dam gives a fall of 175 feet; the fall at Karapiro will be 100 feet, and as the same volume of water will pass through the turbines at both stations the capacity of Karapiro cannot be so great: 90,000 k.w., as compared with 109,500 k.w. now installed at Arapuni. At Karapiro, however, three generating units will produce this great output of power, compared with Arapuni’s six, for rower plant design has advanced fast since Arapuni was planned to the then up-to-the-moment practices of hydro-electric engineering seventeen years ago.