87

D.—]

Khandallah-Petone Railway Section.—Other than prearranged shut-downs, totalling 104 hours, there were thirteen interruptions to supply, totalling 12 hours d minutes, recorded during the year. One, of 7 hours 53 minutes, was due to the breakdown of a transformer supplying solenoids on remotecontrolled air-break switches in the railway-yard ; one, of 5 minutes, was due to the failure of supply from power-house owing to a flash-over at pole 629 on the main transmission-line, while two others, totalling 12 minutes, were due to insulator troubles on the main line ; three interruptions, totalling 2 hours 37 minutes, were occasioned by fires on poles on the Hutt line. Six interruptions, totalling 1 hour 17 minutes, occurred on a Sunday when the Railway Department's feeder was being used by the Power Board to supply Hutt Valley. Of these, two, lasting 2 minutes, were due to overload, and one, of 1 minute, was to enable the overload-relay settings to be altered. Two interruptions, lasting 1 hour 12 minutes, were due to troubles on the Power Board's lines, and one of 1 minute was due to some unknown cause. Khandallah-W ellington Meat Export Co. Section.—Other than prearranged shut-downs, totalling 28 hours 3 minutes, there have been six interruptions, totalling 12 hours 35 minutes, on this section during the year. One, of 4 hours 37 minutes, was due to water getting into current-transformers at the Ngahauranga Works, and one, of 7 hours 38 minutes, was caused by a break in the line where chafing had taken place at a binder ; one interruption, of 5 minutes, was caused by a flash-over at pole 629 on the power-house-Khandallah transmission-line, and two, lasting 12 minutes, were due to insulator trouble on the main line. The remaining one, of 3 minutes, was due to switching operations at Khandallah Substation. Transmission-lines.—General. The third series of tests on insulators by the buzz-stick method is now nearing completion, only a portion of the Bunnythorpe-Wanganui section requiring retests on insulators reported a.s defective after the initial test. All units reported as defective have been replaced with tested units and forwarded to Khandallah for testing on the oscillator. This latter test is a gauge of the efficiency of the buzz-stick method, and generally the results of the latter are confirmed. Generally, all lines have operated satisfactorily throughout the year. A large percentage of interruptions recorded on the main transmission-line was due to salt deposits, which gave trouble in February and March last, after a long spell of dry weather. Such conditions will have to be guarded against in the future, and it is clear that all insulators must be cleaned periodically. It seems not improbable that some means will be devised whereby this can be done under live-line conditions, thus reducing considerably the number of interruptions required for work on the lines. With the commencement of operation of the Waikaremoana Station the existing protective equipments at substations between the two generating-stations became inadequate to cope with the altered conditions of power being fed from either end of the system, and a complete new system of protective gear has been ordered. This will be coming to hand and will be installed during the current year. In addition, a high-tension synchronizing equipment is being installed at the Mangahao Station to enable the two power-houses to be paralleled on the 110 kv. side of the main transformers. At present paralleling can only be done on the 11 kv. bus-bars, necessitating a short interruption on the Bunnythorpe east line every time the two stations are paralleled. Sap-testing has been continued on the poles of the whole system, and experiments have been carried out with a view to arriving at the best means of strengthening poles which show an undue proportion of sap. Several poles have been replaced on the Woodville-Masterton section, and at the present time others are being strengthened by " stubbing." A check has been kept on lightning-storms occurring in the area traversed by Mangahao lines, seventeen being recorded during the year. Only one storm did appreciable damage to the system, pole d 32 on the Bunnythorpe-Wanganui line being damaged by fire after the line had been struck by lightning. Two strings of insulators were shattered, and the lightning-arrester fuses at Wanganui Substation were blown. At the same time one of the Wanganui Power Board's feeders was struck and a potential transformer on their switch-gear at the substation damaged. Another lightningdischarge struck the Bunnythorpe-Wanganui telephone-line, burning through the wire. Substations. The apparatus at all substations has operated satisfactorily throughout the year. Synchronous condensers have been erected at Khandallah, Dannevirke, and Mangamaire Substations, and have been run as required for voltage regulation. _ Two rotating insulators on air-break switches at Woodville Switching-station and one at Mangamaire Substation failed during the year and were replaced. All the damaged insulators were of the hollow type, with which trouble has been experienced previously. New metering equipments have been installed at Khandallah, Bunnythorpe, Mangamaire, Masterton, Dannevirke, and Waipukurau Substations, and the metering-apparatus at othfir stations has been checked during the year. A new substation is in course of erection at Marton, to provide a second point of supply to the Wanganui-Rangitikei Power Board. At Napier Substation a battery-room has been erected and a 110-volt battery installed for 0.C.8. controls. Similar batteries have been installed at other substations in place of the 30-volt primary batteries originally used for 0.C.8. controls. A fire did considerable damage to the garage at Woodville Switching-station, and destroyed a truck housed therein. The garage has since been reconstructed. A considerable amount of work has been done at all substations in improvement of grounds, and at Khandallah a large amount of testing-work has been carried out for the whole system.