D.—l.

Transformers : The 11 kv. bushings on almost all the main transformers had been found to be leaking and allowing the compound in them to drop down into the transformers, necessitating cleaning of the tops of the transformer-cores and filtering of the oil This work, and alteration of the bushings to prevent it, carried on into the present year. Switch-gear : There were four cases of failure of 110 kv. insulators on air-break switches. Five other similar insulators were damaged by the flying pieces of porcelain. 110 kv. condenser bushings on oil circuit-breakers failed in three cases. One 50 kv. bus-support failed. No. 1 Unit—Vibration : No. 1 unit was tried early in April and was found to have the same vibration on load as before. A number of measurements were made of the frequency and amplitude of the vibration, the most striking result being that wear on the pivot ring indicated that the lower shroud of the runner under vibration was displaced or was whipping as much as 7 mm. from its central position. This, however, was very much greater than any bending that could be observed in the shaft, and tended to confirm previous opinions that the trouble was in the waterwheel itself. The frequency of vibration was 455 to 465 per minute. It was then decided to try the runner of No. 3 unit on No. 1, depending on the other two machines to carry the load. No. 1 unit was dismantled and the runner removed between the 16th and 29th January. The pivot ring, which had been badly worn due to vibration and rubbing of the runner on it, was built up by welding and turned to its proper dimensions, and No. 3 unit was dismantled, the runner fitted to No. 1, and No. 1 unit was assembled in the week ending 12th February. No. 1 unit was then tested with No. 3 runner on the 15th February, was found to be free from any trace of dangerous vibration, and was put on commercial load. No. 1 runner was tested for balance, although as a whole it was approximately correct, and it was found that the lower shroud ring near the bottom of the runner was out of balance, whereas the balancing-weight was in the top of the runner. When run at speed the efiect of this out-of-balance on the greater diameter was sufficient to offset the balancing done at no speed on the smaller diameter. This original balancing-weight (about 129 lb.) was removed, and plates of the right weight (totalling about 114 lb.) were cut, shaped, and welded on the inside of the lower shroud ring to balance it. No. 3 unit was assembled with No. 1 runner on it, from the 6th April to the 15th April, and dried out, A newly metalled upper guide bearing was installed during the assembly. It was tested on the 26th April, and ran without trace of dangerous vibration. No. 4 Unit—Tests : Tests were carried out to find the efficiency of the turbine at various loads. The flow of water was measured by twelve Ott water-meters in the penstock, mounted on a bar which was first vertical and then rotated to 60° on either side of the vertical, thus giving velocity at thirtvsix points in the pipe. Five-minute runs were taken at each position of the bar, each meter recording separately on a chr.nograph. The efficiencies thus found were as follow:— Horse-power. Per Cent. Quarter-load .. . . .. .. 5,250 65 Half-load .. .. .. ..10,500 80 Three-quarter load . . .. .. 15.750 90 Full load .. .. .. .. 92-8 Overload .. .. .. .. 25,000 85 With no load on the generator the turbine takes about 180 cubic feet of water per second, and at full load about 1,110 cubic feet of water per second. Horahora (Generators, 10,300 kw. capacity; transformers, 5/50 kv. 11,880 kv.a., 5/11 kv. 2,501 kv.a.). —For part of the year Horahora was run on reduced load, with parts of the station shut down in rotation, but it was found that considerable difficulty resulted on account of condensation of moisture on the windings. Turbines : Two upstream guide castings on No. 1 unit were replaced with reconditioned castings, and two upstream runners and guide castings on No. 2 were replaced with new runners and castings! Generators : In April Nos. 1 and 2 exciter motor stators both broke down and were repaired. On the 16th September No. 8 generator stator broke down and was repaired later. Switch-gear : Two condenser bushings broke down. The local service transformer (100 kv.a.) broke down, due to damage caused by lightning. Grand Junction Steam Plant (1,640 kw. Turbine and Generator). —This plant has not been run during the year. Huntly Steam Plant (1,500 kw. Turbine and Generator). —This plant was shut down on the 14th April, after which a considerable amount of work was done to prevent deterioration of the plant while not in use. Penrose Diesel Plant (3 1,250 kw. units). —This plant was shut down on the 9th April, and was then overhauled. The plant is now given a short run weekly to keep it in order. (b) Transmission-lines. There were two cases of breakdown in service of insulators during the year, as compared with two last year and four the year before. 395 defective pin insulators and 15 strain or suspension units were located by live-line testing or otherwise and replaced, as compared with 326 pin insulators and 29 suspension-type units in the previous year. In addition, 552 50 kv. pin insulators of an old type were replaced by new ones. A total of 42 defective wood poles was replaced, as compared with 65 and 92 respectively in the two previous years. On all lines during the year there was a total of 33 accidental interruptions, due to faults on lines (21) and unknown causes (12), involving outages of the lines on which they occurred of a total time of

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