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D—4

Shortage of coal practically prevented the Golden Bay Cement Co. from using their generating-plant, but the company assisted materially by keeping their demand as low as possible. In an endeavour to prevent rationing, various lakes in the Cobb catchment area were tapped, but for about a fortnight from 10th March rationing cuts of 10 per cent, to 20 per cent, were necessary. The position would have been worse if the various Power Boards and other consumers had not co-operated and practised voluntary rationing. 2. Reliability oe Supply Although the number of accidental interruptions shown on the chart below is 27, no less than 16 were due to snow conditions on the 11 kV. line between the power-house and the dam. Of the remainder, only 5 affected all Power Boards : one on 12th June, 1946, was due to lightning, and the other 4 all occurred on 13th August, 1946, as a result of the screens at the dam becoming blocked. The following table gives an analysis of both accidental and prearranged shutdowns :

Faults and Shutdowns on Departmental System

B. OPERATION AND MAINTENANCE 1. Power-stations Cobb. —The station peak of 8,100 kW. on 14th November, 1946, was a 16 per cent, increase on the 1945-46 M.D. The rainfall from April to December was sufficient to maintain a fair river flow, being continuously above 100 cusecs from the middle of July to the end of December. On 13th August a flood again caused the screens to block, with results similar to those reported last year, and auxiliary stations were quickly brought in. The Cobb generators were off load on four occasions during the day, the total interruption period being 1 hour 33 minutes. During the first three weeks of January the river flow fell gradually and standby plant operated as from the 20th, and by 29th all normal auxiliary stations were operating but the position was still deteriorating. Investigations

30

Year ended 31st March, 1947. Year ended 31st March, 1946. Description. Accidental. Prearranged. Duration. Distribution Authorities affected. 1. 66 kV. lines : Defects 2. 66 kV. lines : External causes 3. 11 kV. lines : Defects i i 2 3 1 H. m. 3 45 5 27 3 05 4. 11 kV. lines : External causes J •• \ l 1 0 06 0 30 5. Lightning l / 0 04 \ 0 27 17 06 0 18 0 08 5 06 *2 1 6. Storms 7. 6-6 kV. apparatus 16 i 3 8. 11 kV. or 33 kV. apparatus { :: *6 9. 66 kV. apparatus 10. Generators 11. Relays 12. Control circuits and batteries 13. Operation: Mistakes 14. Operation: Accidents 15. Faults and overloads on consumers' systems 16. Other causes 17. Causes unknown l i l 3 i 6 1 1 3 41 0 *02 f 0 01 1 33 I 0 05 0 03 *3 1 Totals 8 27 17 41 36 9

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