85

D.—l

operating equipment has been cleaned and overhauled. The turbines and generators have operated very satisfactorily during the year, practically all trouble being due to broken turbine buckets. In order to cope with the increased demand on the station a new set of nozzles, slightly larger than the originals, has been purchased. These are now to hand, and will be fitted when the Waikaremoana Station is able to take over the bulk of the load on the system, thus releasing the local machines when required. Transmission-lines. —110,000-volt Lines. Mangaore- Khandallah Line. —During the year there have been nine complete interruptions on this line, totalling 22 hours 17 minutes. Of these, five interruptions, totalling 22 hours 2 minutes, were due to trouble caused by salt spray on insulators; two, totalling 9 minutes, were due to unknown causes ; one, of 4 minutes, was traced to a flash-over ; while one, of 2 minutes, was due to a switching error at the power-house. In the light of subsequent experience it is reasonable to assume that the interruptions on this line due to unknown causes were actually -caused by salt spray on the insulators. This line has been thoroughly overhauled, and is now in good order. Mangaore - Bunnythorpe Section —West Line. —This line has been in service through the year, supplying power to the Manawatu-Oroua and Wanganui-Rangitikei Power Boards. Other than prearranged shut-downs, totalling 6 hours 10 minutes, there have been nine interruptions to service, totalling 5 hours 18 minutes, and these were all caused by salt deposits on the insulators on the Bunny-thorpe-Wanganui section of the line. The lengthening of junipers and hanging of weights on the Bunnythorpe-Wanganui section have been completed, and this line is now in good condition. Mangaore - Bunnythorpe Section—East Line.—This line has been in service during the year for the supply of power to Hawke's Bay and Wairarapa, and since the end of January, 1929, for the supply of power from the Waikaremoana Power-station to the Mangahao system. Other than prearranged shut-downs, totalling 2 hours 16 minutes, there have been nine interruptions to service, totalling 2 hours 13 minutes. Two interruptions, totalling 42 minutes, were due to the failure of rotating insulators on the air-break switch at Woodville Switching-station, while another interruption, of 3 minutes, was possibly due to a fault in one of these insulators which later failed completely; one interruption, of 8 minutes, was traced to a flash-over at an air-break switch at Waipukurau Substation which brought the line out at the power-house. Pour, of a total duration of 54- minutes, were due to flash-overs caused by salt deposits on insulators ; and one, of 26 minutes, was due to some cause unknown. The lengthening of jumpers and hanging of weights to the revised schedule have been completed, and this line is now in good condition. The groyne at the Manawatu River crossing has been cleared of debris and a few more willows planted to fill gaps. Bunnythorpe-Wanganui Line. —Service to the Wanganui-Rangitikei Power Board has been given on this line during the year. Interruptions recorded total forty-four, of 127 hours 16 minutes duration. Of these, twenty, totalling 15 minutes, were traced to faults on the Power Board system, which tripped the 0.C.8. at Bunnythorpe ; two, totalling 4 hours 40 minutes, were due to a lightningstroke which set fire to a transmission-line pole ; twelve interruptions, totalling 33 hours 55 minutes, were due to line troubles caused by salt deposits on insulators ; one, of 12 minutes, was occasioned by switching operations, during the transfer of load to the Waikaremoana Power-station, whilst another, of 10 minutes, was due to the failure of supply from that station ; two interruptions, totalling 3 hours 47 minutes, were necessitated by troubles which developed in parts of the equipment at Wanganui Substation; while for the remaining one, of 18 minutes, no cause has been found. During the period that trouble was experienced due to salt deposits on insulators this length of line suffered rather severely. Investigation showed that one make of insulator gave somewhat low value of leakage resistance, and it was therefore decided to remove those of that make from this section of line, substituting insulators of higher leakage resistance. The line has been patrolled regularly throughout the year and trees cut where necessary. Bunnythorpe-Woodville Section. —Other than prearranged shut-downs, totalling 5 hours 42 minutes, there were thirty interruptions to service, totalling 4 hours 36 minutes. Three interruptions, of 1 hour 7 minutes total duration, were due to the failure of rotating insulators on an air-break switch at Woodville Switching-station, while three others, totalling 10 minutes, were probably due to the same insula tors before they failed completely ; five interruptions, totalling 21 minutes, were caused by surges when tests were being carried out on the synchronous condenser at Napier Substation ; one interruption, of 8 minutes, was due to a flash-over on an air-break switch at Waipukurau Substation which brought out the line at the power-house ; one, of 10 minutes, was due to trouble at the Waikaremoana Station ; and two, of 7 minutes total duration, were occasioned by switching operations when changing the load from the Mangahao to the Waikaremoana Station ; one interruption, of 8 minutes, was probably due to a jumper on the Mangamaire-Masterton line being blown into contact with a cross-arm during a gale, and one, of 5 minutes, was due to lightning ; three interruptions, totalling 57 minutes, were caused by salt deposits on insulators ; ten, totalling 1 hour 13 minutes, were due to causes which could not be ascertained. A close watch has been kept on the Bunnythorpe-Ashhurst section of this line for cable-strands broken by vibration, but during the year no trouble of this nature has been encountered. At pole No. 177, near Ashhurst, a parallel-groove clamp was tightened under live-line conditions. The line has been patrolled regularly throughout the year and trees cut and tracks cleared where necessary. Generally this line has given good service, and at the present time is in good condition. Woodville-Mangamaire Section.—Other than prearranged shut-downs, totalling 37 hours 49 minutes, there have been forty-two interruptions to service, totalling 10 hours 16 minutes, on this line during the year. Of the remainder, thirty-one were due to the same causes as on the Bunnythorpe-Woodville