6.s6 



NATURE 



[October 31, 



1895 



for the central and northern district, and an alternating-current 



high tension S)-stem for the southern and eastern district, both 

 sj-stenis being workeii from one central station, and under the 

 same control and management. A good site was found for the 

 central station between the Caledonian Railway and Dcwar Place. 

 The lioiler-house is designed to contain seventeen iKiilers, of 

 which at present only six are in place. They are of the dry- 

 liacked marine type, each lol feet mean diameter and 12 feet 

 long, with two I'urves flues 3I feet inside diameter, and 166 

 tubes of 3 inches internal diameter. The boilers are of steel 

 with H rought-iron tubes. On the top of the boilers are fitted 

 super-heaters, each having two nests of lubes enclosed between 

 the top of the boiler shell and a fire-brick casing above. Each 

 consists of thirty-two vertical flat coils of wrought-iron tube I A 

 inches diameter. Sinclair's mechanical stokers are fitted to each 

 Uiller, and are driven by an electric motor. The main steam 

 pipe forms a complete ring round the present boilers. This ring 

 joins the engine-room main at two points, and is provided with 

 valves, so that the failure of any one pipe will put only the cor- 

 responding Ixjiler out of use. The pump-room contains at pre- 

 sent one duplex steam pump and two three-throw pumps driven 

 electrically, each pump specially designed to run with a large 

 range of Sjieed, and for this purpose can be connected with either 

 the 230- volt or the 115-volt mains. A Kennedy water meter is 

 connected w ith one range of feed pipes, so that the whole of the 

 water going to the boilers can be measured. In the pump-room 

 is placed the electric motor for driving the mechanical stokers 

 with its counter shaft. The coal brought in the railway trucks 

 is at present stored in the exst end of the l)oiler-house ; on the 

 .station t)cing extended, the coal will l)e stored over the boiler- 

 house, and let down through shoots to the mechanical stokers. 

 In designing the plant at present in the boiler-house, proWsion 

 for extensions has been kejit in mind, and the arrangements are 

 such that new plant can be added at any time. 



The engine-rooms are side by side, forming really one room 

 divided by a line of columns which carry the roofs and the beams 

 for the travelling cranes. The engine-room next the boiler- 



1- ' - -^"rved for the low-tension plant, the other contains the 



plant. A platform, raisetl 4 feet above the engine- 



I ;vel, nms the whole way across the west end of both 



engine-rooms ; and on this are placed the switchboards and 



regulating gear for both the low- and high-tension .systems. The 



machinery at present in the low-tension engine-room consists of 



eight engines, four of 100 I.H.P., two of 250 I. II. P., and two 



of 360 I.H.I'., with their dynamos; and pronsion is made for 



eight more engines of 360 I. II. I'., in the future. All are 



Willans central-valve engines driving their dynamos direct. All 



the dynamos arc two-pole shunt-wound machines with drum 



armatures, all wound to give 270 volt.s, except two which are 



driven by two lOO I.H.P. engines ; these two are wound to give 



135 volts, Ireing used as balancing machines on the three-wire 



.system. The steam-piping forms, with part of the boiler-house 



ring, a complete ring round the low-tension engine-room, and is 



connecte<l with the boiler-house ring at two points. The main 



ring is 8 inches internal diameter throughout. The straight 



lengths are of .steel, with thick flanges .screwed and br.azed on ; 



the tee pieces and valve lx)xes are of cast-iron ; and the bends of 



copper with steel flanges. All I>ends are of large radius, and no 



-ion joints are used or retjuired. The engines are elected 



■ -, and are connected with the main ring by two long copper 



The pi()es are slung l)ylong rods from brackets fixed on 



ills or columns, so as to allow free movemeiil. The main 



■t pi|)cs are of cast-iron, and arc led throvigh a Uerryman 



• alcr, in the Iwiler-housc to the chimney. Provision is 



I' If three more heaters when reijuircd. The whole of the 



' on a concrete fiundalion block 7i feet thick, 



troni the foimdations of the walls. 



from the dynamos are drawn through curved 



^ let into the concrete, into chases in the centre 



ndation block, along which they are carried to 



I under the .switchlioard platform. The leads from 



•lin-; off (he machines arc also carried in the same 



l.iiing resistances ; the switches for these 



■ .n the handrail on the platform in front 



leads from the resistances being brought 



■'f the handrail. The swilchlHiard, and 



f.itus for regidaling the dynamos and the 



id for the distribution of the current, are placed on 



ii, and are ilireclly under the eye of the engineer in 



ch.'.r,^-. 1 he switchlxiard consi.sis of seven slnlc panels, c-ach 



NO. 1357, VOL. 52] 



about 7 feet high, and stands 4 feet from the west wall of 

 the engine-room. The arrangement of the switchboard and 

 conductors was next described. 



The battery-room has a fire-proof floor covered with acid 

 resisting asphalt. The batter)- consists of 132 cells of the new 

 Crompton-Howell 31-plate type. It is divided u|) into two 

 half-batteries, ixjsitive and negative, and is arrangeil in two 

 tiers on four rows of stands, which .are of cast-iron, with wooden 

 longitudinal l>earers carrjing the cells : the eight hospital cells 

 are arranged on separate stands. All the cells are similar, and 

 have each a nominal capacity of 1000 ampere hours, the normal 

 rate of discharge being 200 amperes. The Ixattery has ample 

 capacity to meet the whole of the load of the station from day- 

 light till the evening ; thus during the .summer lime it can do the 

 lighting during more than half the twenty-four hours. The 

 high-tension portion of the station consists at present of only 

 two engines anil alternators with iheir switchlxjard, and the 

 rectifiers for arc-lighting with their regulating arrangements and 

 switchboard : but in the immediate future, this plant will be 

 considerably extended. Each of the alternators is driven direct 

 by a Willan's three-crank engine of 150 I.H P., on the same 

 bed-plate. The alternators arc of the "Portsmouth" type, 

 with some modifications necessary owing to their increased 

 speed of 450 revolutions per minute. Their armatures are 

 stationary, and are of great strength ; the core, consisting of 

 sheet-iron .segments, is solidly bolted into the framing of the 

 machine, with the coils threaded through holes in the sheet-iron, 

 well insulated, and completely enclosed in brass boxes. The 

 field magnets revolve, an<l consist of two heavy cast-steel discs, 

 having on their circumference claws projecting sideways altern- 

 ately over the field winding, which is between the discs, and is 

 well protected from injury. The exciting current is taken from 

 the low-tension switchboard at 230 volts, and is only a few 

 amperes. The alternali>rs work at an electromotive force of 

 between 2000 and 2200 volts with a fre<)uency of 52.J figures 

 complete alternations per second. Opposite to the alternators, 

 and standing on the same foundation block, are placed the 

 Eerranti rectifiers for the series arc-lighting. These are three in 

 number, one for each of the Iwo circuits, and one to spare. 



In the three-wire system of distribution lor the northern and 

 central districts, the electromotive force between the two outer 

 conductors, positive and negative, is 230 volts, while that between 

 the middle wire and the positive or negative is 115 volts. The 

 latter is the electromotive force of the lamps on the consumers" 

 premises, no trouble being now experienced in obtaining glow- 

 lamps to work at this electromotive force, or even higher. The 

 feeders from the station are connecleil to the distributing mains 

 at sixteen points They consist of two conductors only, the 

 positive and negative ; the middle wire is interconnected 

 throughout as much as possible, and is brought back from three 

 districts on the system. The cables are put in parallel at the 

 station, and .one connection only is made to the switchboard. 

 The positive and negative sides respectively of all the feeders 

 are put in parallel at the switchboard : but any feeder or feeders 

 can be put on a separate machine if rcipiired. As far as po.ssible, 

 consumers in each street and district are balanced .against one 

 another by connecting them alternately between positive and 

 middle wires, and between negative and middle wires; large 

 consumers have all three wires taken into their premises, ami 

 their lights balanced against one another in a similar manner. 

 But however carefully this balancing is done, it is impossible li' 

 gel a really accurate balance ; the " out of balance " curreni 

 varies from hour to hour, and even from minute to minute, and 

 is diflerenl on diflerent days of the week. The amount out of 

 balance is compen.sated for at the station by means of the 

 balancing machines, ime of which can be put on either side of 

 the sy.stem ; the Italancing during the light load is done fnun the 

 battery alone. Eight wires, forming potential le.ads or pilot 

 wires, are brought Iwck from all three conductors at each feeding 

 point, and are conneclcd to the feeder volt meters on the switch- 

 board ; .so that the pressure at the feetling points at any part of 

 the system is directly known at the sUlion, and the necessary 

 regulation made for keeping the electromotive force constant. 

 The distributing mains are brought back lo the station, but ate 

 used only for the su]iply of light and power ihere ; no regulation 

 is done on the mains anywhere, except lo the feeding [MjinlS. 

 No high-tension feeders or distributing mains have yet been laid, 

 but will be added later. 



In regard lo road-work, practically the whole of the dis- 

 tributing mains are laid as cable insulated with in<liarubbcrj 



di: 



