D.—l

The survey of the 50 kv. duplicate line from Tuai to Euakit'uri was carried out, but, due to the unsatisfactory nature of the foundations, the final plans have been delayed pending a more intensive investigation. The survey of the Masterton-Melling 110 kv. line was started and a considerable amount of location work has been done. A survey was made of the Khandallah-Ngahauranga 11 kv. line for the Wellington-Paekakariki railway electrification. Other survey-work was carried out on the Mangahao-Khandallah, Woodville-Masterton, and Napier-Waipukurau lines. A design was prepared for a wood guy-insulator, which it is proposed to use on all guys in future. Several were made up and tested, the results of the tests being very satisfactory. (d) TELEPHONE SYSTEM. Radio-telephone transmitting and receiving sets are being installed at Mangahao and Waikaremoana power-houses. These will facilitate communication in the event of the telephone-lines being damaged by earthquakes or other causes. A new motor-generator ringing-set is also being installed at Mangahao to aid in ringing Arapuni. 2. Operation and Maintenance. (a) POWER-STATIONS. Mangahao Power-house and Headworks. —This part of the system operated very satisfactorily during the year. The water-supply was well maintained generally, but in November and December the level in No. 1 dam fell 41 ft. 3 in. below normal, due to the dry weather and the fact that Waikaremoana was out of parallel. In February and March the dam had to be emptied to enable repair- work to be carried out. The rainfall at No. 1 dam was again below the average, amounting to 113-24 in. During the winter damage was caused to the power, telephone, and indicator lines to the headworks, due to heavy wind, rain, and snow, as much as 2|r in. of snow being observed on the wires on one occasion. Some very large slips, which blocked access to No. 1 dam, had to be cleared during the year. At No. 1 dam advantage was taken of the low water-levels to overhaul the automatic gates, all the steelwork being scraped and painted. In February a failure occurred in the disperser-valve which, under normal conditions, is used to regulate the flow of water from the dam, to prevent wastage of water from No. 2. The valve apparently stuck and became too stiff to be operated by the motor. The dam was emptied, and the valve dismantled and thoroughly overhauled. An ammeter has now been installed in the motor circuit so that a check may be kept on the operating-condition of the valve. While attempting to open the by-pass tunnel sluice-gates to empty the dam trouble was met with, due to the accumulation of rust and debris on the rollers and sliding faces. The gate was thoroughly cleaned and painted, the rollers and sliding faces being well greased. A further survey was made in connection with shingle deposits in the dam, but the results have not yet been plotted. At No. 2 dam the cushion-pool was pumped out and examined. A survey was made of the pool and the toe of the dam, and any erosion that has taken place has not affected the stability of the dam. Plans have been prepared to place concrete, where required, to prevent further erosion. The water-level recorder was shifted to a new position nearer the clam and a stone retaining-wall was built to prevent debris falling on the sill of the automatic gates. Damage has been caused by this debris in the past, when the gates have been operated under flood conditions. Willow and flax planting has been carried on at Arapeti (No. 3) dam. The main pipe-lines were inspected internally and are in good order. An 8 in. diameter drainvalve was fitted to one 72 in. pipe just below the surge-chamber, and both pipes were scraped and painted externally. Nos. 4 and 5 bus-pipes were sandblasted and painted internally, the deepest pits being welded. A noteworthy feature is that sandblasting was successfully carried out in pipes as small as 24 in. and 27 in. diameter. In addition, the main valves at the entrance to the power-house were replaced by straight pipes and the tee in No. 5 was removed and used to replace the cross in No. 4 pipe. These modifications have improved the hydraulic efficiency of the pipes considera-bly. While sandblasting was being carried out on the bus-pipes Nos. 4 and 5 turbines and governor gear were completely overhauled. After ten years' continuous service on heavy loading the turbines and governors were in very good condition. It was found necessary to fit bronze bushes to the needlevalve operating-rods, and provision was made for better lubrication of the needle-shafts. Minor repairs to the governor-gear were carried out. After cleaning and drying out the generators, comprehensive governor tests were carried out on both machines. The protection of concrete-brick walls and apparatus in the power-houses against earthquakes was completed. Alterations to the main-system diagram-board were carried out and a smaller one was made up for the telephone-booth. An earth-indicator system was fitted to the D.C. bus-bars, emergency trips were fitted to the II kv. cubicle-doors, and the station earthing-system was strengthened. Waikaremoana Power-station and Headworks. —The variation in lake-level during the year was 6 ft. and the average discharge was 512 cusecs. The average rainfall was 68-27 in. Experiments were carried out tripping the pipe-line gates with a view to improving the closing of these gates under load conditions. Further work will be carried out after experience is obtained with the new gates at Mangahao.

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