D.—l.

There were also nine faults on the Department's system which were cleared without causing an interruption to supply to any consumer. Due to faults on the Department's system, supply to Khandallah Substation was interrupted on four occasions during the year of a total duration of 42 minutes. The most serious one, of 27 minutes, was due to a flashover caused by a gorse fire under the Mangahao-Khandallah transmission-line near Pahautanui. The average number of interruptions to each of the eighteen consumers was five, faults on the Department's system being responsible for four of these. The average duration of each interruption was 37 minutes, but, excluding seven major interruptions, details of which are given below, this time is reduced to 6-3 minutes.

Major Interruptions to Supply during Year 1936-37.

The following table gives a comparison of the causes of troubles on the Department's system over the last three years : —

(3) General. —In addition to the normal routine duties, several special features were dealt with. A commutator-grinder was designed to facilitate the trueing-up of slip-rings and commutators, and is attachable to the various generators, exciters, and synchronous condensers on the system. So far this has been used only at Mangahao Power-station, but has come up to all requirements. In connection with the additions to accommodation required at the various substations and powerstations, standard designs for a five-roomed cottage and a single men's quarters were prepared. Investigations were made in connection with the supply of power to the East Coast Railway works, particular attention being given to the loading-conditions on the line. The load during June, 1937, has been very heavy, and, due to the new units at Arapuni being late, it has been necessary to give a considerable amount of study to the operation of the system. The operation of the system under overload conditions has required from the operators of all power-houses very close attention, and, considering the limited facilities at their command, they are to be congratulated on the way in which they have carried out their duties.

85

T ' ' j : Consumer. Duration. Remarks. Hrs. Mine. Dannevirke Electric-power Board 3 02 Pothead on main 11 kv. cable at Dannevirke blew up. Horowhenua Electric-power Board 2 57 Fault on Power Board's system. Opossum came into contact with Mangaore-Shannon 11 kv. line. New Plymouth Borough Council .. 16 00 Due to lightning in Taranaki District. Interruption prolonged, as Borough Council was able to carry its own load. Poverty Bay Electric-power Board 4 57 Jumper on 50 kv. A.B.S. at Tiniroto pulled out of socket due to solder melting. Wairoa Electric-power Board .. 8 44 11 kv. cable-box in Wairoa Substation failed. A twophase supply was maintained for 2 hours 43 minutes of this period. Lake House . . .. .. 4 281 Both due to failure of an 11 kv. transformer at OneThomas' Mill .. .. .. 4 28 J poto. Total time .. 44 36 11 r ■

Year ending 31st March, 1935. 1936. 1937. (1) In 11 kv. apparatus .. .. .. 4 . . g (2) In 50 kv. apparatus .. .. .. . . 1 1 (3) In 110 kv. apparatus .. .. .. 6 10 4 (4) On 11 kv. lines .. .. .. . . 3 1 3 (5) On 50 kv. lines .. .. .. . . 1 5 1 (6) On 110 kv. lines (defects) . . .. . . 2 (7) On 110 kv. lines (external causes) .... 6 3 6 (8) Generators .. .. .. .. .. 3 (9) Relays .. .. ... .. .. .. 3 Operation— (10) Mistakes .. .. .. .. 3 3 2 (11) Accidents .. .. .. 1 5 2 (12) Errors of judgment (13) Lightning .. .. .. ,. 13 8 5 (14) Earthquakes (15) Unknown causes .. .. .. .. 6 5 4 Totals .. .. .. .. 45 47 34