WELCOME RELIEF

Evening Post, Volume CI, Issue 18, 21 January 1921, Page 8

WELCOME RELIEF

MORE POWER FOR THE

TRAMS

NEW TURBINE IN OPERATION

FIRST OF KIND IN NEW? ZEALAND.

This time last year there was trouble with the trams. Almost every day, and particularly in the afternoon, there were prolonged stoppages, and people had to wait or 1 walk.• It was awkward and in-' convenient, but there was not much grumbling. Everybody knew coal was short, and what there was was inferior. It'was left at .that,, but could the scenes inside the power-station at Wakefield- | street have been witnessed, the public would have been t more than sympathetic with the'men whose heavy duty it was to try to keep the cars moving. The war had left the station under-boilered and under-powered for anything but normal running. When it came to overloads at, rush hours, the power fell below the demands made on it, and the' system came to a standstill. STRENUOUS TIMES FOR STAFF: The station was designed for Wellington's original electric tramway system, and the extensions of track and increase in number of cars running and passen-: gers carried last year exceeded its capacity. More boilers were wanted and more power to furnish the motive current for the cars. Inferior coal was the last straw to the over-worked engineered They toiled often twenty-four hours at a stretch, sometimes without food; once they went well over into the second day trying to get the system to work. It was a strenuous, trying time. The first help came in -a- big water-tube boiler of tremendous steaming capacity. It was rushed up with all epeed" under temporary cover, put at one© into commission, and at last there was enough steam and to spare to enable' some of the old type boilers to be overhauled and repaired. But it was not sufficient. to the purpose to have plenty of steam, if the engines could not take it. Engines cannot be forced beyond a certain limit with safety, and for months there were precarious times, when the load, soared up. ' ■ .. : SIMPLE;IN PRINCIPLE. Relief has come at last,, after weary j waiting., in a new type^-for New Zealand —of steam' turbine and generator,: and, for the 'time' being at any rate, anxiety as to power is removed.. The steam turbine is, of course, not new in itself to Wellington. There are two excellent examples in the big electric- . light station'in fiercer-street, visible and audible to passers-by at any hour of the ,'day.-.or night. But they are simple compared with the new factotum, handyman turbine in the tramway power house." The. steam from tlie boilers passes, through the series of fixed and ■moving.blades, and expends its energy .in turning. the big rotor with its many rings of blades, and thus in direct consequence by a direct,connected shaft the ereafc dynamos .which generate the current for'lighting the.city. . The turbine hums round at between 1000 and 2000 revolutions per minute, and the armature of the dynamos at the same speed. In its principle it is the simplest engine , in the whole world, yet easily the most powerful. The battle-cruiser' New Zea-' land and the battleship Renown are ■ driven by similar turbines. GEARING DOWN. Thore are striking differences in the r.eSv. turbine for the tramways. In the first place it is a geared turbine. It has been found by practical experience that the turbine runs best at highspeed, and the dynamo—especially a direct current dynamo, with' its delicate commutator— at comparatively low speed. It ie obvious the higher the speed of the turbino, the smaller, it need be for a given output. " The actual rotor in the new machine is. only about a yard . in diameter at it 3 largest in the low:pressure stage—much smaller than the electric lighting' turbines. But it inns at twice the speed—<JGOO revolutions a minute, so that eveTy . blade in the low pressure rotor travels over seven miles in that; time. The armature of the dynamo' revolves only 500 times a minute to the turbine's 4000. The reduction of speed is effected by a,special typs of gearing, the result of countless experiments to!avoid the obvious dangers of transmitting huge powers through geaTs. The teeth are cut by a special machine on. a helical curve and are termed "creepcut." To prevent any distortion in the shaft reacting on the fine teeth c>f the gear-box there is an electric coupling be- I tween the'turbine and the gearing. Lubrication is under light pressure. , . MIXED STEAM PRESSURES. •''j . Tho turbine itself has-been described as a. factotum; it will run ,on high; pressure steam direct from the boilers or on tho exhaust steam from the old 'triple expansion engines of the original plant, or it will take both at the same time. It is a mixed-pressure turbine. Tha value of, such a generator in the tramway station is obyious. The reci[•locating, piston-in-cyiinder ' engine is not economical at its low-pressure /stages; the turbine then shows its greatest economy. . The exhaust steam from one or more of the reciprocating engines—the turbinewill actually take the exhaust from the two 600 lew. reciprocating sets—comes to the turbine at about atmospheric pressure, and 13 thero utilised through the range between atmosphere and a vacuum of 28£ inches—practically a perfect vacuum. Or, if more power is needed to carry the load, the turbine will take the exhaust from one reciprocating set and high-pressure steam from the boilers at tho same time. Or, again,'it will take high-pressuro steam alone. Itself the turbine is in two stages, a small, cylindrical high-pressure section and a lowi pressure .section of larger diameter. Steam can be admitted at the high-pres-sure end through a special valve, or by a valve halfway into the low-pressure stage. Yesterday afternoon, when a Post representative had an opportunity of viewing the plant, it was running; on mixed pressure, the exhaust from a 600 k.w. reciprocating set and high-pressure steam from the boilers. The'speed was just on 4000 revolutions per minute, ana the output approximately .1000 k.w. This is the output ior 'high-pressure ' steam alo.ne and for mixed pressures. The output is 300-400 K.w. on exhaust steam alone, .when the high-pressure stage runs idle in a vacuum. SUCCESSFUL RUNNING. The new turbo-generator, therefore, with its varied capacity for work, will prove a most valuable help to the power station, which, by modern standards, is old fashioned. It will enable some of the engines to be overhauled and insure adequate power for some time'to come. Provision is also being made for the installation of a reciprocating set from the electric lighting,station, and the exhaust from this will be coupled up with the new turbine. The economy in consumption is reckoned with the new turbine at from 20 to 25 per cent., and the extra power at 1000 k.w., sufficient for rum ning new' cars and new . extensions. The work 'of erecting the new turbine plant was carried out by Mr. F. Merchant, of' the power-house staff, without the aid of any expert from the makers

and under great difficulties. Special ad justnients had to be mide to meet the conditions here, and these could only be determined by the most careful testing and experiment. A . modern steam turbine runs with extraordinarily fine clearances of its blades, measured in thousandth's,of an inch. Any disturbance of tile balance of the heavy motor running at "WOO r.p.m.. "might prove. disastrous-. It may be added that, beyond the. actual turbine plant,' there is a, large condenser needing special equipment lor the high vacuum required, and it was riixessary also to inatal a new circulating° pump and system to lift water from the harbour. .All this work has been: carried out under, novel conditions with a sue-, cess that reflects the. gri-atest credit on the engineer and staff.