ELECTRIC LIGHT SERVICE.

Taranaki Daily News, Volume LIII, Issue 136, 17 September 1910, Page 7

ELECTRIC LIGHT SERVICE.

EXTENSION OF PLANT IMPERATIVE. MR. F. BLACK'S REPORT. In his report to the Borough Council on the extension of the power station plant, Mr. F. Black, A.M.1.E.E., writes as follows: LOAD CONDITION'S AND GENERATING PLANT. From my examination of the station working I find that the generating plant is now called on to take the maximum peak loads without there being any reserve capacity. Though the maximum load occurs only during a few weeks in winter, the position is none the less a serious one, and requires that steps he taken without delay to enlarge the plant. In this matter I agree fully with the borough electrical engineer's recommendation as to the urgency of the need; no public supply undertaking should under any circumstances be dependent upon the full use of every generating set in its station to enable the maximum demand of the consumers to be met. It speaks well for the plant and for the care it receives that it should have carried the peak loads of last June and July without mishap, tbut the risk of failure is too great, and the department's duty to its consumers and the public is such that a reserve of plant is imperatively required. In the event of a tramway load being added to the existing load, the maximum demand on the station by the winter of 1-912 may be estimated at 300, kilowatts (400-horse-power). I have very fully considered what addition to the present plant capacity should ibe made in order that this load may be. undertaken and a proper reserve provided. The matter requires that the number and sizes of the existing generating sets be taken into account, and, more important still, that a definite policy of enlargement for the future be laid down—the present extension of plant to be the first step in carrying out the policy, and succeeding ones to be'on lines uniform with it. My conclusion is that a standard size of 2.00 kilowatts should be adopted, but expressly on condition that two such sets be installed forthwith, and that when the times comes for adding a third set—which I estimate will be in 1914—both the present 45-k.w. sets should be, removed and the new one erected in their place. It may be objected to this that 400-k.w. is an excessive addition and. will for a year or two Teduce the profit now being made by the department. The reply to this is that the station is now running with a tbtal plant capacity altogether too small to comply with sound engineering and commercial principles, and therefore in bringing it up to a correct standard, in providing for a tramway load, and in allowing a proper margin against the growth of the next three years, the increase recommended is not more than is necessary. As regards the present rate of profit it is only possible to make this ibv taking risks of breakdown and interruption to the serviceman other words, by working the entire plant up to its limit —so that some reduction (qot necessarily of the present total -amount, but of- the rate per cent, earned) will be inevitable when the station is equipped with the full quantity of plant it ought to have. Dealing with the position should the station not be required to supply tramway power, the winter maximum peak load is now slightly over 160-k.w. In three years' time it will be, at the average rate of growth, 250-k.w. The borouogh electrical engineer's recommendation that a 200 kilowatt set ibe installed cannot now' be given effect to in time to enable this set to carry the whole of the maximum load of its first winter of service (1912). This, means thSt the reserve capacity of the station plant will then be insufficient to provide for continuity of supply if any temporary trouble occurs with the set. In my opinion the only safe course is the one recommended in the former case, viz., to now fix upon a standard size of set for all future additions, and to instal two sets at the earliest possible moment. In no other practicable way than this can the essential requirements of reliability of service be met. The choice practically lies between 150 and 200-k.w. On the whole I favor the larger size, because in the long run it means a lower capital cost for a given capacity, it places the undertaking in a position to meet a considerable increase in the demand', it simplifies the station design by reducing the number of sets that will be contained in it, and because it should lead to still more efforts to enlarge the scope of the business.

WATER POWER AND HYDRAULIC - WORKS. My visit to the headworks and the information gained from the station engineer left no doubt in my mind as to the sufficiency of the water in the Waiwakaiho for generating much more power than is required now, and more than enough for the next few years. The tunnel is of ample size to carry several times it« present maximum flow, and to effect this increase a dam acvoss the river is necessary. It should be concrete or ferro-concrete and of a height to raise the normal level of the river not less than four feet. Its site can only be determined after a detailed examination of the river-bed and banks by making iborings, but an apparently favorable place is that opposite the high ground, five chains below the intake to the tunnel. There is no occasion to fear a scour effect upon the unlined portion of the tunnel by doubling the present flow of water through it. The section of tunnel under the Mangamahoe creek, though not, as constructed, of smaller area than the tunnel elsewhere, has practically become so iby the silt, which I am informed •has .deposited in its dip. It would be best to raise the crown- of the tunnel at the crossing, and that it is advisable to do this prior' to building the dam and increasing the water pressure in the tunnel. The effect of this work will be to dam the Mangamahoe creek and raise its level perhaps a foot at that point, but this is a matter of no importance whatever. I do not recommend taking the creek water into the tunnel. As already noted, less silt will come through the tunnel after the dam is built than is the case now, tout I consider that notwithstanding this it is desirable to provide means for the settlement of such amount 'as will still come, and for the efficient straining of the water from leaves and semi-floating matter. The importance of admitting the water into the pipes only when free from sand, leaves and; sticks is great, and as the existing chamber at the pipe-head must in any event be altered, I recommend the construction of a concrete forebay having sufficient area to p.ermit of silt deposit and equipped with steel strainers and cleaning platform. The additional pipe line required from foreibay to station should be capable of delivering approximately 3600 cubic feet of water pei minute—sufficient to run at full load two 200-k.w. sets, with some margin over. The diameter would be four feet. When

eventually a third 200-k.w. set is installed, this main and the two existing 21in ones would furnish the full load quantity of water for the three sets. _ There is no necessity, in. my opinion, for making any alterations at the present time, to the tail race

TRANSMISSION LINE AND VOLTAGE. ) I concur with the borough electrical engineer that transmission of 2000 volts is no longer suitable or economical, and that a pressure of 8000 volts is desirable. The fa?-' license, however, provides for a maxi mum of 2300 volts on the one line. In the past obiection has been taken by the Government to proposals fo |" . SOOfcvolt overhead wires on country roads, and it aims at restricting pres sures on similar lines within boroughs to 3000 volts. Before tfie existing line could be used for 6000 volts new msu latprs would be necessarv, .andl in seekin*. permission to use this vo tage it would be desirable to arrange for some further alterations designed to meieas in other respects the present factor of safety. This applies to. the line outeid the borough, but as regards thai, pal t within it, I am unaible to sav whetha the Government could.be induced to give permission for a higher pressure than 3000' volts. If the disused railwaj site within the borough were fenced off and could be reserved exclusively for the lin , I think that ought to merit a favorable consideration of the case. Under the system proposed for th tramway, there is no reason win the energy supplied to the motor-converters should not be taken from the ordinary suddlv and therefore a separate transmission line for traction use is not neccssary. It will at times be convenient to use the.smaller of the two existing cir-| cuits (No. 4 wires) for the tramwav supply only, and at the suggested higher transmission voltage the other circuit(No. 0 wires) will be of ample size to take the lighting and power oad for a long time to come. I consider that this arrangement should be adopted for the scheme proposed. ' j COST OF, WORIvS. I have been able, to make only an approximate estimate of cost, , a * a erable amount of data must be derived from a closer investigation of subsoil and other conditions than was practicable for me to carry out m the limited time -available. The f°llo w ing are my estimates of the cost under the different heads:— Hydraulic works .. •• • • » Station plant > . Sub-station plant .. • • • • Transmission line and alterations £10,780 Engineering and con tingencies, 10 per cent .... *'»'? . . ; £11,858