After Six Years—Steam Plant Superseded

Greymouth Evening Star, 20 September 1932, Page 12 (Supplement)

After Six Years—Steam Plant Superseded

’J’HE steam generating plant situated near Dobson has done its duty well during the past six years, and has now been superseded by the hydro, scheme. The fate of the Dobson installation is at present indefinite, the question as to whether it should be disposed of, or retained as a stand-by plant, being still undecided by the Board. In the circumstances, a brief description of the steam plant should be interesting.

The total cost of the installation was £38,000. The contractor for the erection of the power-house was Mr. J. A. Hart, of Greymouth, the amount of his tender being £4,989 18/-. The tender of the National Electrical and Engineering Co., of Christchurch, amounting to £24,611 10/- was accepted for the supply of the plant. The work was commenced about the end of April, 1925, and was completed in February, 1926. Power was switched on to the Board’s first consumer, the Grey Valley Collieries, on April 4, 1926.

i Alternating current at 6600 volts ; was generated by means of two Curtis i turbo-generators, steam for driving I which was supplied by two Babcock J and Wilcox water-tube boilers. The boilers were fitted with a chain grate, which carried the coal from an overhead hopper into the furnace. The speed of the grate and the depth of jthe fire could be varied to suit the j amount of steam required for the tur- ■ bines, in accordance with the variation 'of the power load. Induced draught j was utilised for supplying air to the I furnace. A large fan, driven by a

15 horse-power motor, situated at the end of the flue, drew the burnt gases through the flue and deliveied them up the funnel. Steam was generated at a pressure of 200 pounds to the sciuare inch, with a corresponding temperature of 383 degrees Fahi. This temperature was increased to 483 degrees by means of super-heaters, which were connected to and formed part of each boiler. There were two turbines, each a separate generating unit, of the Curtis high-pressure twostage impulse type, the product of the British Thomson-Houston Co., Ltd. The admission of steam to the turbines was controlled by an oil-driven Servo motor, the direction of this supply being controlled by a centri-fugal-force governor, sensitive to the impulse of the turbine. The governor was" adjusted to maintain 3000 revolutions per minute. If the revolutions exceeded this number, the governor directed the oil supply to the Servo motor, to act in an anti-clockwise direction, and thereby close the steam control valves. As the speed decreased,' the oil supply was changed, and operated the Servo motor in the opposite direction, again opening the control valves. By this means, the revolutions were, kept constant. A quantity of oil was by-passed from the governing system, and maintained at a pressure of 10 pounds per square inch. This supply was delivered to the bearings, and returned to a settling tank, being cooled before again entering the governing system. The steam, after doing its work on the blades of the turbines, entered a surface condenser, and, when condensed, was pumped from the bottom of the condenser to the boiler feed tank. From there, it was pumped through a heater, and delivered again to the boilers at a temperature of 200

degrees Fahr. A water-driven air pump was connected to the condenser, and maintained a vacuum from 28 to 29 inches of mercury. The circulating water for the condensing tank was taken from the Grey River, only a few yards away, by means of a twin centrifugal puinp, driven by a 50 horse-power motor, situated in a concrete house above the level of the river. The three-phase alternator and direct current exciter were directly coupled to the turbines in. each case. The current from the alternators, at 6600 volts, was stepped up, through the transformers, to 11,000 volts, and was distributed through four mains at that pressure. The switchboard was of the truck panel type. Each of thp eight trucks could be drawn out entirely clear of the bus bars, thus securing positive safety when adjustments were necessary on any panel. A Tirril voltage regulator was installed, which maintained a constant voltage at any load. A local feeder panel, supplied with current at 400 volts through a step-down transformer, supplied the station with power for the motors and lighting. Each of the generating sets could be run independently, or could be electrically coupled as the demand for power required.

The Dobson plant was described as conforming to the most modern engineering practice, both electrically and mechanically, in regard to duplication, efficiency, and economy. Its’ capacity was 1250 kilowatts, and this was fully required within a comparatively short period. The result has been that the Board is now “off with the old love, and on with the new”— the Arnold hydro, plant, with a capacity of 2500 kilowatts at the pre-, sent head, but capable of much greater development.

September 21, 1932, should be a redletter day in the history of Greymouth, and the Grey district, when the hydroelectric power is turned on, but as every red-letter day on our calendar does not register a pleasant memory, it is to be sincerely hoped that September 21, 1932, will register one. The scheme has cost Greymouth, especially, a great deal, and but for the projection of the hydro loan at the time it was voted for, Greymouth would undoubtedly have had a satisfactory wat-er-supply and a much-improved drainage' system; but the borrowing of £130,000 for the Arnold scheme precluded any possibility of carrying loan proposals for these necessary works, with the result that the Borough has to do the best it can with an inadequate water-supply and unsatisfactory drainage, and provide the major part of the hydro security.

This is the more regrettable since, by spending £30,000 on the extension of the present steam plant, all the power that can be safely relied on from the present works could have been obtained, and a permanent demand for 800 tons of slack coal per month would have been established, which would have enabled from 1600

to 2000 tons of face coal to be mined land sold and constant, employment found for probably 50 miners and others; the circulation of £l2OO monthly in wages in addition to local railages, royalty and wharfages. This,

as I pointed out when I made use of your columns to oppose the hydro scheme, would have been a much better idea than paying an extra £5OOO per month to the bondholders, whose returns are not always used for industrial advancement. However, the men most vitally interested in the team scheme thought otherwise, and i lie clear majority of 100 votes that Ruaanga gave hydro carried the day. In view of the number of days that the mines are idle because they cannot sell their slack coal, and conse--'uently cannot produce screened or round coal, I often wonder if the vote had to be taken now, how it would go. It has always to be borne in mind that, when in the early days of the Power Board’s operations, the Arnold River was measured in a very dry season—l forget for the moment whether by Mr Lythgoe or the late Mr. Gillies —it was found that 3000 kilos could not always be relied on. Incredible statements were being made then that the Arnold River had been seen flowing back into Lake Brunner, and were even repeated to the Government party who visited the Arnold River, when the first engineer to the Board reported that he could bring in the hydro scheme and reticulate the boroughs in the Board’s area for £BO,OOO, a statement which could not be substantiated. I especially mention this in view of the alleged intention of the Board to dispose of the steam plant

as soon as the hydro takes over the load.

The history of hydro so far in NewZealand has not proved that it provides all that its advocates claim for it, and certainly on tfie West Coast it never will while suitable coal can be got at present rates. When the comparative costs of steam qnd hydro were being investigated by the first members of the Board, they had, the advantage of the late Mr. E. Turner, Christchurch City’s Electrical Engineer’s experience in Christchurch, and his advice summed up was, “While coal can be got at 16/- per ton, never look at hydro.” At that time, in view of the Government’s intention to more than double the price of juice to the Christchurch City Council, he found that with coal at 48/- per ton, with the then available load he cduld countei’ the Government rate successfully. This was the time when in self-defence Christchurch City Council investigated the Otorama Gorge scheme at a cost stated at £BOOO, and prevented the Government’s .excessive impost. . It is to be hoped that, notwithstanding the success that may be achieved bv the hydro scheme, the Board will take ample time to consider the possible results that may ensue should the steam plant be disposed of. During the whole period of steam it is safe to say that no uncontrolled stoppage of powei- has occurred, and if at any time such should occur it can be quickly located and as quickly repaired. This cannot be guaranteed in hydro, and as now practically the whole of the .mines employing mechanical ventilation, pumping and haulage power, -with the possible exi ception of Blackball, are dependent on i the Board for power, any serious ac- ‘ cident happening to the head works ■ would in its effects to the Grey dis- . trict reduce the present economic • slump to a forgotten circumstance, s The finding of the necessary deprecia- . tion on the stand-by steam plant ■ might be a tax on the Board, but it s would be a well-invested insurance ; premium in the interests of the dis- ; trict.