D.—l

(6) Insulator Deterioration. —Live-line testing of all insulators in service was carried out with the following results : —

Total number tested .. .. .. .. .. .. 129,111 Total defective .. .. .. .. .. .. ■ • 235 Percentage defective .. .. .. .. .. •• 0-182 The above table does not include 50 kv. pin type insulators. (7) Survey of Lines. —The check survey of the Woodville-Napier line was completed and that of the Bunnythorpe-Wanganui line is under way. The resurvey of the Mangahao-Khandallah lines is being checked. (d) TELEPHONE-LINES. An analysis of all the interruptions to telephone service, of which there was a record in the powerstation logs, was made back to January, 1931. It was found that there had been a total of 503 interruptions in the period. These were grouped into eight general causes, with about forty separate individual causes within these general subdivisions. It was plain that no general cure could be devised, and that it would be necessary to deal with individual causes and eliminate them one by one. To this end a Telephone Interruption Report was instituted from which a complete analysis can be made from time to time, and with causes definitely ascertained suitable remedies devised. Vibration breaks, as a cause, have now disappeared, due to the installation of dampers, and the elimination of the bulk' of the other causes is within sight. (e) COMMUNICATION SYSTEM. The question of telephone protection against induced voltages received further attention, and the basic data for the design of insulating transformers for use with a mid-point earthing system of protection were calculated and submitted to manufacturers. A case occurred where an insulating transformer was by-passed due to the use of a separate earth for the telephone arrester, with the result that in several substations the telephone lightning-arrester earths have now been bonded to the main station eath. An investigation is in progress to determine the distribution of substation equipotentials, and this will determine whether a reversion to separate earths for the telephone system is feasible. (/) TESTING. The usual six-monthly maintenance tests on all relays and meters were carried out in accordance with the schedule. Various special tests were carried out in the test-room and in the field ; these included tests on a pumping equipment and special tests on the radio transmitters at Mangahao and Tuai, with a view to incorporating crystal control. Phasing problems were investigated and alterations supervised ; arrangements were made for the routine testing of all rubber gloves in the district; inductive interference tests at Titahi Bay and Tawa Flat were witnessed ; several 110 kv. fuses were reconditioned ; and new contacts were designed and made up for the automatic tripping devices at the Mangahao surge-chamber. In addition a number of tests were made on meters and metering equipments for various supply authorities, both on site and in the test-room. (g) GENERAL. (1) Load. —It was not found necessary to call on standby plants during the year. The maximum load on the system was 55,160 kw., as compared with 55,120 kw. last year. However, if the output from Evans Bay Power-station is included, this year's maximum demand was 63,100 kw., an increase of 14-5 per cent. The total output was 305,709,291 units, or 307,580,890 units including Evans Bay output, an increase of 12 per cent, over last year's total of 274,728,861 units. The annual load factor was 55-6 per cent, as against 56-7 per cent, last year. The Mangahao-Waikaremoana system was operated in parallel with the Arapuni system throughout the year, and the following are the details of the interchange of power between the two systems, last year's figures being given in brackets : — From Arapuni— Maximum demand .. .. .. .. 20,840 kw. (19,800 kw.) Units supplied.. 52,858,752 (38,414,250) To Arapuni — Maximum demand .. .. .. .. 6,620 kw. (12,830 kw.) Units supplied .. .. .. .. 98,788 (319,901) (2) Reliability of Supply. —During the year there were thirty-six faults causing interruptions to consumers, twenty-two of which originated on the Department's system and fourteen on consumers' systems. Of these, nineteen faults on the Department's system and nine faults on consumers' systems paused a total interruption to the 11 kv. bus-bars at one or more substations.

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Strain. Suspension. Total number tested — 110 kv .. .. .. •• 24,084 102,019 50 kv 1,814 1,194 Total .. .. .. .. 25,898 103,213 Number defective — 110 kv. .. .. .. •• • • 28 207 50 kv. .. .. .. • • Nil Nil Total .. .. .. .. 28 207