D.—l

95

The lighting and wiring of the plant were overhauled. On the 23rd January broken cross-head bolts on the air-pump of one turbine set resulted in considerable damage to the pump, and the set was out of service for repairs until the Bth March. The Junction plant was not called upon to deliver its maximum capacity until the present winter, and its maximum supply to date was 3,400 kw. in June, 1929. Diesel Plant, Penrose. The erection of the Diesel plant was completed in May, 1928. (See last annual report.) Trouble very soon after operation started, mainly in pitting and corrosion of the exhaust-valves, owing to unsuitability of the atomizers for use with the fuel oil supplied. A large number of trials were run with different adjustments of the engines, but without much improvement, and finally the makers were asked if they could supply new atomizers suitable for the oil available. In the meantime arrangements were made to get a sufficient supply of another oil from the Admiralty fuel-tanks at Devonport, and from October to the end of January this oil was used, with satisfactory results. Tests were made early in February, using the original oil with the new atomizers on No. 3 set, with good results after a number of adjustments had been tried, and arrangements were therefore made to change over completely to this oil, which has been used exclusively from the 21st April, 1929. Operating troubles with the engines have been principally due to carbonization of oil, both the cooling-oil in the piston-heads and the lubricating-oil in the air-compressor. On a number of occasions carbonization of the cooling-oil has resulted in blockage of the supply of oil, and on one occasion deposit of carbon inside the piston-head has reduced the cooling effect, this resulting in burning of patches on the piston-head, followed by slight cracking at the burnt patch. Carbonization of lubricating-oil in the air-compressor results in blockage in the intercooler, requiring the set to be shut down until the blockage is removed. In June, 1928, shortly after starting up, a bolted joint in the piston cooling-oil system of No. 1 set came adrift, causing failure of oil-supply and slight seizing of the piston on the cylinder-liner, scoring the latter so that it had to be replaced. In addition to the foregoing, there have been a number of minor troubles on smaller parts, requiring frequent attention and occasional replacement, but on the whole the plant has worked satisfactorily. It has been in regular operation since September, 1928, two units running nearly all the time on full load on six days a week from 5 a.m. to 10 p.m., and three units running occasionally when required. The maximum load carried to date was 4,240 kw., on the 24th April, 1929. 11,000-volt Lines and Substations. There has been little trouble with these during the year. Eight decayed poles were replaced in August on the Horahora Leamington section. Power purchased and generated by Stand-by Plants. Power purchased during the year amounted to 12,776,370 units, including 10,514,730 units from McLaren's Falls and 1,762,070 units from the Auckland Power Board, the latter being mostly obtained in September, 1928, following the fire at Horahora. In addition to this, the Grand Junction plant supplied 5,046,740 units and the Diesel plant 7,070,912 units, a total of 12,917,652. The total units from all these plants was thus 25,694.022, or approximately one-quarter of the total output, as compared with one-eighth for the previous year. Interruptions. Due to 50 kv. Transmission-lines. —Athough interruptions to supply have been more numerous than usual for the year, this has been due rather to the extraordinary conditions of operation than to actual defects in the lines. No insulator breakdowns have occurred on any of the following line sections: WaiorongomaiWaihou, Waikino-Kerepeehi, Waikino-Aongatete, Horahora-Arapuni, Horahora - Mystery Creek-Te Awamutu - Hangatiki, Mystery Creek - Hamilton, Horahora-Hamilton-Bombay-Penrose (110 kv. construction), Penrose-Henderson-Takapuna. The Horahora-Waiorongomai section was responsible for seven interruptions due to insulator failure, one due to a turkey flying into the line, one to trees falling across it, and one to binders and mechanical clips broken in a storm. The Waiorongomai-Waikino section was responsible for four interruptions due to insulator failure. On the Bombay-Kerepeehi section one insulator failed during the year, punctured by lightning. There were no other faults on this section. On the Arapuni-Ngongotaha section there was one flash-over at the time of a severe lightningstorm, and later on pole 77 was discovered to have the top burnt off, with no insulators damaged, but with the telephone and power wires in contact, this being responsible for an interruption of 12 hours 28 minutes. On the Ngongotaha-Edgecumbe section lightning shattered one insulator at pole 320, burning about 2 ft. of the pole-top, and causing an interruption of 17 hours 38 minutes. In addition to the foregoing, there were nine interruptions due to unknown causes, in most cases more than one line being affected.