OVERLOADED

Dominion, Volume 12, Issue 152, 22 March 1919, Page 8

OVERLOADED

CITY'S ELECTRIC PLANT

LINKING THE MANGAHAO SCHEME CONSIDERABLE EXPENDITURE NECESSARY. The extension of Wellington electrical plant and tho changes that will bo rendered necessary by the introduction of power from tho hydro-electric station at Alangaliao wero tho subject of a report to the City Engineer by the electrical engineers of- the. tramways department and the electric lighting department. This report, which was placed beforo the City Council on Thursday night, shows that considerable capital expenditure will bo necessary during tho next year or two, apart from any measures that may be undertaken in connection with tho hydroelectric scheme.

"Tho maximum load of tho lighting station during the past year," states tho report, "was 1520 amperes, or approximately 3010 kilowatts, and this load was carried by the two Parsons turbines, tho combined capacity of which is 3000 kilowatts. Since last winter there has been an increase of connections, consequently our load during tho coming Winter will be in the neighbourhood of 3100 k.w.

"The maximum load of the tramway station during tho past was 3200 k.w., obtained from a. plant having a total capacity of 3000 k.w. From tho above figures it will bo seen that the combined maximum demand of the two stations during tho coming winter will bo at least 6450 k.w. To meet this demand we aro going to be very hard pressed, more particularly through the lack of boiler capacity. Orders have 'been placed for two boilers,; one: for either station, but it is practically a certainty that they will not be erected in time for this winter's load.

''To meet the ever-increasing demand for electricity it will bo necessary to instal additional machinery, and in our opinion this new plant should be designed with a. view to fitting in with the proposed hydro-electric scheme if it is adopted by the city. This will necessitate considerable alterations in our present system of generation and distribution. Tho hydro-electric scheme .will supply current at 11,000.volts,.three-phase, 50 periods, and after careful consideration we aro of opinion that the electric lighting station should be made the stand-by station and distribution centre for the new scheme. This opinion ,is based on tho grounds that there is already a complete equipment of water-tube boilers and ample room for future extensions on this site. A stand-by plant of GOOO kilowatts could be kept in readiness there, this stand-by plant to consist of the present two 15(H) k.w. turbines, the generators of which will require to be altered to meet the new conditions, and a new 3000 k.w. set which will be designed for the new conditions. This machine should bo ordered at the earliest opportune moment.

"Air extensions to plant in the meantime should be made from tho present liffhting station. When the hydro-electrio scheme is available and has been adopted by us, the 11.000-volt feeders would be brought into the station and'transformed down for distribution on tho present lighting mains. This will entail altering our periodicity from ■80_ to 50 cycles. The magnitude of this will be apparent when we inform you that there aro 1100 transformers and about 15,000 meters which will be affected by the change. Considerable alterations will lie necessary to tho mains, as the current supplied will -he three-phase, and we propose to run our three-phase feeders to predetermined points, the ultimato distribution being on llie'single-phase system. "We Tiave written to the _ makers, Messrs. Parsons, asking for their advice on the feasibility of altering the existing generators to meet the new conditions. In all probability they will recommend us to instal now-generators. Tho change in our system will also entail considerable alterations to the switchboard.

"At the present time there is approximately 0000 h.p. connected to tho d.c. feeders, tho largest proportion of which is supplied from an independent feeder system. There is also about. 2000 h.p. in motors supplied from the lighting station. We are of opinion that at the present lime there is nothing to warrant us in going to the expense of altering the d.e. system, but should tho be sucli iii the future as to warrant us in adopting' the three-phase, system it can be easily and economically carried out then. Tlie'alteration in tho i'reeiuency will necessitate the replacing of all motors at present connected to the lighting station. This expense will have to be borne by the council.

"Tho generating plant in tho tramway powerhouse is at present perionsly overloaded, and although the position will be greatly improved when the plant now on order is delivered thexe will be comparatively little margin to meet tho increasing demands of the traffic department and power consumers. The tramway_ feeder system is'at present loaded to its full capacity, and to obviate tho necessity of laying down a large amount of low-ten-sion feeders to convey current from the powerhouse' Steps should be taken to instnl a. sub-station in the southern end of the city .at an early date. The supply for this sub-station will require to be. obtained from the new plant to be installed in tho lighting station transmitted at a pressure of 11,000 volts, which will necessitate the installation of step-un transformers in the lighting station. The substation plant will require step-down transformers and, rotary converters to convert the a.c. supply to 500 Tolls direct current. It is estimate that two converters witli a capacity of 500 k.w. will bo required for the sub-station in its initial stage. The positive an'd-return feeders system in the southern' end of tho city will require considerable alterations to meet the new requirements. I "From the above it will be. seen that the adoption of tho hydro-electric scheme is going to entail large capital expenditure, with its attendant increase in annual capital Anrges. This must be taken into account, when considering the financial position, as increases in capital charges must be debited against any saving which nuiy be effected in generation charges."