Bay of Plenty Beacon Published Mondays, Wednesdays and Fridays, WED. MAY 28, 1947. VISIT TO KARAPIRO

Bay of Plenty Beacon, Volume 11, Issue 34, 28 May 1947, Page 4

Bay of Plenty Beacon Published Mondays, Wednesdays and Fridays, WED. MAY 28, 1947.

VISIT TO KARAPIRO

BAY ELECTRICIANS Members of the Bay of Plenty Electricians’ Institute recently travelled to Karapiro and Arapuni to inspect the hydro electric works. Following is a report of the visit.

About half a mile off the main highway and about three miles on the Rotorua side of Cambridge lies the most modern hydro-electric power station in New Zealand, and when fully completed' capable of supplying into the power line of the North Island 90,000 kilowatts. Karapiro—like Arapuni—has a fairly large residential area which is situated above the dam on the road side of the river. The power station and dam provide a great sight looking down from above. Behind the dam is the newly-formed lake, stretching fourteen miles long and approximately a mile wide in the widest place. This vast area no doubt will be the haunt of yachting regattas, fishing and picnics. The dam is of solid reinforced concrete, 576 feet long, and 100 feet from waterlevel to the roadway which is situated on the top of the dam with convenient passing places. The foundations of the dam' are 43 feet into the river-bed and set below sea-level. It is 57 feet wide at the base up to the road width at the top. The lake level is controlled by three self-priming siphons placed one above the other. The purpose of these is that in the event of heavy rain the siphon with its inlet at the lower level will automatically commence work and so in turn will numbers 2 and 3, so keeping the lake at a constant level. However, if in "the event of a heavy flood the siphons will not control the rise, the spillway gates which weigh fourteen tons would be raised by a travelling crane. From the top of the dam to the power house, which is about 80 feet below, an electric lift-conveys visitors and workmen, with an alternative of several hundred steps. On the eastern side of the dam is the diversion tunnel which had to be built to take all the water flowing down the Waikato before the dam proper could be commenced. This tunnel is of concrete and is 1000 feet long and 27 feet in diameter. This has now been closed by a gate weighing 100 tons and will need to be disturbed only in the case of major repairs to the dam. There will be three units in the power house capable of producing 30,000 kilowatts or in simple terms about 40,215 h.p. At present there is only one unit completed and this is not yet fully tested.

These units are of the vertical type and run at a speed of 176 revolutions a minute. 'An idea of the size of these units may be gained when it is stated that one unit weighs 2760 tons. All the operations of the alternators are recorded in the control room. This is a beautifully finished room with panels all along one side on which are mounted instruments in separate sections for each alternator. The attendant can tell at a glance such things as voltage frequency, power factor etc.

This station like all the others through the North Island is worked into the grid system.