This is an article taken from Engineer and published when the first Blackwall Point Power Station was opened in 1900. The article is a bit long and some of it quite technical but it contains some very interesting insights into the setting up of what was a new technology - electric light - and selling it to the public.
BLACKHEATH AND GREENWICH ELECTRIC LIGHT COMPANY'S CENTRAL STATION.
The Blackheath and Greenwich District Electric Light Company Limited, whose generating station and system of distribution forms the subject of this article, started life by obtaining a provisional order empowering it to supply electricity if Greenwich and Blackheath about the year 1897: but no active steps were taken to put into operation the powers and obligations of its order until 1898.
The London Electric Supply Corporation had already obtained powers to supply alternating current in the Greenwich area, and the Board of Trade, in the exercise of their discretion, limited the Blackheath Company to direct current supply throughout, but subsequently consented to allow it to supply alternating current in that part of the district which includes Blackheath, Lea , Charlton, Kidbrook, and part of Lewisham and Eltham still reserving the original limitation as to a direct supply in Greenwich.
One of the terms imposed by the local authority, as being a condition of its consenting not to oppose, was that the company should within two years of the granting of the original order apply for similar powers covering a very much extended area. and embracing some small villages that could not otherwise hope to get any electric light for many years to come. The extended area covers seventeen square miles, and lthough this company' has not applied for what is popularly described as a power Bill such as the Tyneside, Durham, South Lancashire and others , recently before Sir James Kitson's Committee in the House of Commons its obligations and prospects are in many ways identical. And the problem it had to face was to some extent complicated by the fact that it was compelled to supply direct current in the Greenwich area.
The problem was very thoroughly considered, with the result that it was decided that, having regard to all the circumstances, a two phase alternating system would be better suited than any other to the requirements of the districts embraced, more especially as the company was approached by a local tramway company to supply power for driving the tramway as soon as the company should have obtained the necessary parliamentary sanction.
These powers have since been granted, and the company will, therefore be probably called upon in the immediate future to supply current to the cars from the same station that now supplies the lighting load.
A site, covering 2 acres 1 rood and 4 poles, having a frontage to the river at Blackwall Point, was obtained, and although situated on one of the boundaries, it was apparent that the advantages of coal supply, condensing facilities &c., would more than compensate for loss in transmission on the trunk cables; but for some presumably good but non -apparent reason, having purchased the site with those advantages, it was forthwith decided to ,make no use of them. and at the present moment the steam is not condensed, and the transferring of the coal from the barges to the bunkers is done entirely by hand. and must cost £200 or 300 a year or more.
The original scheme included, in addition to the rails on the wharf a coal conveyor, by means of which a 600 ton collier could have been emptied in twenty-four hours into a 70 ton bunker situated immediately over the boilers and it is to be hoped that something of the kind will back adopted in the near future. the penny-wise policy, of cutting down capital expenditure in labour has so often been condemned, and is so palpably unfair to the shareholders, that it is to be hoped that the company will take the earliest opportunity of abandoning it in favour of more rational methods.
The question of condensing is one which has been very fully discussed and the policy in electric light stations has almost universally been to postpone the expenditure on the condensing plant until the load is so large that it is comparatively constant. There are, indeed, electric light stations in this country in which the condensing plant put in is so large that the steam required to drive the air pumps is more than the amount saved by condensing and they are consequently used only for perhaps three or four hours a day. The result is that the amount of capital that remains unproductive for hours a day is increased although the actual total spent on plant is slightly less than if the top load were dealt with non-condensing or to be more accurate, might less if the introduction of condensers actually reduced the expenditure on generating plant.
As a rule it is not until the station has passed through the lean years and is established as a successful undertaking that any attempt is made to increase the year’s dividends by reducing the coal consumption in this way. To digress for a moment, let us assume that the expression ‘load factor’ means the ratio of the average to the maximum possible rate of production. We shall probably be justified in stating that with the existing load factor the coal consumption at Blackheath is equivalent to 23 lb.-Welsh steam coal-per unit sold. It will be admitted that the load factor will materially improve as time goes on, and the coal per unit sold will be reduced. At the present moment with a bad load factor the coal consumption is a larger item in the total cost of production than it is ever likely to be again, and it would therefore seem to follow that it is more important to reduce the coal consumption now than later on when the conditions of the load have so far improved as to make the coal a small, instead of as at present a large, proportion of the total cost of production.
(l) Condensing plant, provided that it is capable of dealing with the average load over a twenty four hour day. If, as is reasonable, we assume (1) a 10 per cent load factor; (2) a coal consumption of 16 lb. per unit; (3) a saving of 20 per cent due to condensing; (4) maximum load of 600 kilowatts. Then it follows that our total saving per annum equals:
- 626 tons of coal saved per annum.
(2) If on the other hand, a condensing plant is provided for condensing the maximum load, this can only be used economically for two hours per diem.
Then on the same basis, except that the coal consumption per unit must be taken as 8 lb, since the rate of production reduces this figure, we have as our total saving per annum
The company's site has a frontage to the river of 227ft and a substantial timber and concrete wharf has been built. The front piles 38ft to 45ft long and 13in. square are driven at 9ft 9½ ins centres with a batter of one in twenty four, the wing wall piles being 12 in by 12 in with l0 in centres. A line of 6 in thick sheet piling is carried the whole length of the wharf, the top of it being embedded in concrete. The bearing piles are 9 in by 9 in. The anchor piles are 12 in by 12 in. All piles were driven till the last six blows of a 20 cwt ram falling 6 ft. drove them less than 3 in. Swivelling mooring hooks are provided, instead of the usual bollards. These hooks are anchored back diagonally, just below the surface of the concrete, to two of the main anchor piles. The wharf has a road-metalled surface, and a fall of 12in. from the engine-room wall to the drains which discharge on to the river front. Fifty-six-pound Vignoles rails run from end to end, and two turntables arc provided, one connecting with a set of rails running right inside the engine-room so that machinery delivered by boat can be taken off the truck, under cover, by the engine-room traveller,and placed at once on the foundations. The difficulty of handling and erecting new machines is not as a rule sufficiently considered: but this arrangement meets the case very well, and should save trouble and expense in the future. The other turntable communicates with another set of rails which runs down the side of the boiler house over the coal bunker so that coal may be taken out of barge or colliers and shot straight into them.
The station buildings are not in themselves interesting from an architectural point of view, but a great deal of difficulty was experienced in their construction at first, owing to the dangerous condition of the subsoil, which contained two veins of soft peat.
The old river front consisted of an artificial clay bank said to have been the work of the Romans, but the ground behind this bank and several feet below the top of it was made ground, and was very largely composed of soapworks refuse and soft rubbish; in fact no solid bottom could be obtained for the walls or engine foundations without going down to the ballast which was found at depth varying from 28ft to 35ft. below the finished surface of the wharf, which, according to Thames Conservancy regulations, is 5ft. 6in. above Trinity high water mark.
The expense of taking the foundations to such a depth would have been enormous and the results in a water logged soil would have been doubtful, and it was consequently decided that the whole building should be built on piles. Pitch pine piles have been used throughout, uncreosoted. Another consideration that led to the adoption of the piles was the danger of causing damage to surrounding property by draining the water out of the subsoil. The entire block of buildings now stands on piles. These piles are arranged so as to distribute the load as equally as possible and carry approximately 20 tons each. For example the steel stanchions supporting the gantry and the roof on the east side of the existing engine-house will, when the engine-house is extended laterally, be called upon to carry something like 100 tons, and they are therefore supported on five piles each 30ft. long and 12in. by 12in. section fitted with 201b steel pointed shoes driven about 3ft into the ballast. The heads of all the piles are cut off level 9in above the finished surface of the excavation, which then covered by 3in. float of concrete in which the heads of the piles are buried.
Another feature of the buildings which we noticed is the fact that there are no skylights. The walls below the gantry are not available for windows, and the lighting has been affected by putting in windows in the walls between the roof and the traveller rails.
The buildings generally are very substantial, and eminently suitable for the purpose for which they were designed. A comparatively small additional expenditure would have been sufficient to make them more architecturally beautiful. This spirit of rigid economy has not, however been carried to excess the engine room walls are faced with white glazed bricks, and all the brickwork is set in cement.
The buildings at present erected include engine house, boiler-house, pump-house, and shaft and occupy an area of 11,515 square ft. The inside dimensions are as follows, engine house 104ft. 2in by 35ft. 71/2 in; boiler house, l03 ft 6in by 46ft. 1in; pump-house, 25ft. 1½ in. by 16ft 6in
The boiler-house is designed to accommodate six Babcock and Wilcox water-tube boilers of 250 horse power each, and two Green’s economisers. The engine house will accommodate the engines at present installed, together with an additional engine of any size from 500 to 1000 indicated horse power
The shaft for the boiler house is built on a concrete float 40ft square and 9 ft thick, containing in all 583 cubic yards of concrete and weighing 720 tons. The height of the shaft is 198ft. from the concrete float. For a height of 4Oft. The base is square; it then becomes round, and continues so for the rest of its height. The inside diameter of the shaft at the top is 9ft. The total weight of the shaft and foundations is about 1700 tons. The firebrick lining is continued up the shaft for a distance of 60ft., the thickness being 9 in at the top and 14 in at the bottom, the maximum air space being 4 ½ ins and the minimum l 2/3 ins. The boiler house plant at present installed consists of three Babcock and Wilcox water tube boilers, each capable of evaporating 10,000 lb. of water per hour at 160 lb. pressure. The grate area of each boiler is 51 square feet, and the heating surface 2852 square feet. The boilers are of the double-drum type, the two drums being each 23ft. 7in. by 3ft. 6in., and connected by a cross drum fitted with one main 7in stop valve mounted on the top. Each boiler contains 126 4in tubes. The economisers are not at present installed, but provision has been made in building the main flue for installing them in the future. There will be four economisers, each consisting of 96 tubes.
The boilers are fed by two Evans horizontal ram pumps. The steam cylinders being 6 in. and 10 in, the ram being 5 ½ in, and the stroke 12 in. The feed water is heated by two Chevalet heater detarteriseras, which extract the scale from the water, and in doing so heat it to 212 deg. Fah. By means of the exhaust steam from the exciter engines. These heater detarterisers the use of which is comparatively new in electric lighting stations, consist of a series of trays in each of which the water comes into contact with the exhaust steam. The heat thus Imparted to the water boils it, and freeing all the carbonic acid in solution causes the carbonate of lime to be deposited in the form of a soft scale in the bottom of these trays. The calcium sulphate is also deposited by mixing common soda with the water as it enters the heaters. This combines with the sulphate thus:
CA SO4 + NA2 CO2 > NA2 SO4 + CA CO2
The sodium sulphate is soluble in the water, and the calcium carbonate is thrown down in the heater tray. The sodium sulphate is prevented from concentrating in the boilers by blowing them down occasionally. The scale is very easily removed, the trays being lifted up by the traveller immediately overhead, and run on to a platform which forms the ceiling of the pump-room. Here they are lowered and stood on edge and cleaned out in a few minutia. One of these heaters can easily be cleaned and set to work again in a morning. The oil in the exhaust steam, which might otherwise prove a nuisance, is extracted by a separator before the steam enters the heater, and what little does remain is thrown down with the scale in the heater trays. No trouble is experienced owing to oil being carried over with the exhaust steam. Immediately over these heaters is placed a water tank 16ft 6ins 24ft by 4ft. This is supplied from the water company’s main, and is provided with an indicator, fixed in the pump house, to register the height of the water in the tank.
The systems of pipe work in use at this station are interesting on account of the flexibility obtained by the arrangement of valves and interconnections. The system adopted consists of a ring main placed vertically against the boiler house Wall. The boiler branches enter the lower part of the ring immediately over pockets at the bottom of which a drain is fixed which is connected to a steam trap and so kept free from water. The engine branches are taken off the top half of the rig and through the engine room wall straight to the engines. This system while giving flexibility to the steam ring isentirely devoid of water troubles and, moreover as all the valves are visible to anyone operating any one valve, mistakes such as sometimes occur with ring mains are here entirely avoided. The valves are all of Hopkinsons make. And are in every case fitted with a small bypass. The two horizontal steam mains are connected at each end by a semicircular steel bend.
The system of jointing in use consists of a ring of copper 1/12 in thick and ¾ in wide placed between the faces of flanges which are screwed and welded onto the pipe, and then turned dead true. The joint is tightened up by means of bolts placed through Cast Iron collars which are loose on the pipes. This form of jointing gives excellent results, and reduces the repairs to pipe work to a minimum. The feed piping system consists of a 4 in ring feed main with the valves and suction pipes so arranged that either half of the rings can be used for hot or for cold feed. Throughout all the pipe work in this station there is no one joint which if it were to give out would under any circumstances cause a failure in the continuity of the current supply.
Having now dealt with the boiler house plant, we will proceed with the engine -room plant, which is the more interesting on account of its two phases alternators. Briefly the engine-room plant may be divided up into two sets. First the high speed engine driving the direct coupled “day load” alternators and their exciters and, secondly, the larger slow speed horizontal engines driving fly wheel alternators Which latte are excited by continuous current dynamos driven by separate high speed engines. There are two “day load” sets, each consisting of a Bellis, high speed compound engine and a Johnson and Phillips two phase alternator and exciter running at 375 revolutions per minute. The diameter of the high pressure cylinder is 12ins, of the low pressure cylinder 2Oin, with a stroke of 9 in, the brake horse-power is 190 and kilowatts 125. The approximate weight of each combined plant is 17 tons. The engines are fitted with Bellis usual system of forced lubrication in an enclosed crank chamber. The alternators are of the fly-wheel type, and were built by Johnson and Phillips giving a normal speed 8000 volts on each phase. The coils in the armature which is stationary, are wound in slots in the iron core each coil being enclosed in a micanite tube. Ring lubrication is used on the alternator bearings. Each machine has its own exciter coupled onto the end of the alternator shaft and each exciter is capable of supplying suffocate current to excite both day load sets should such an emergency arise.
The heavy load plant at present consists of two Clench engines with fly wheel alternators, also built by Johnson and Phillips, running at 90 revolutions per minute. The indicated horse power is 450. They are cross-compound horizontal engines, the cranks are overhung, the crank disc being keyed and shrunk on to the shaft. The following are the principal dimensions of these engines: - high pressure cylinder diameter 19 in, low-pressure cylinder diameter 37 in, stroke 38 in, indicated horse power 400, approximate weight of engine is 20 tons. Approximate weight of flywheel 17 tons; diameter of piston rods 3 1/2 in; diameter and length of crank pin. 6 in; diameter of shaft in Journal 10 ½ in; length of Journal 21 ins; diameter of shaft in fly-wheel boss 31 in; length of journals 24 ins. The piston rods are extended to form a tail-rod and thus minimise the wear on the cylinder liners. The valve gear for steam admission on both the high pressure and low pressure engines is worked by a trip motion, and it is on this trip that the engine governs - the governor being dead weight and being also adjustable by hand while the engine is running. The exhaust valves on both cylinders have a direct motion and are a modification of the ordinary sliding grid type. All valves and the governor are driven on a secondary motion shaft which is itself driven off the main shaft by worm gearing enclosed in an oil bath. The beds of the engine are formed of heavy box castings with hand holes for all holding down bolts.
The alternators are wound in the same way as the day load sets. There are 64 coils in each phase making total of 128 coils in each machine. The diameter of the fly wheel to the edge of the field magnets is 11 ft 10 ½ ins. the number of field magnets is 64. The approximate weight of each alternator is 30 tons. The field magnets are bolted on to the periphery of the flywheel. The peripheral speed of the poles of the magnets is 50 ft per second, and the periodicity of the alternators is 50 complete cycles per second. Steps are provided down into the alternator pits so that in case of a coil burning out it can be replaced easily and without 1oss of time.
The exciting current for those alternators is supplied from separately -driven exciters. Of which there are two each being capable of supplying the exciting current for all the machinery that will be contained in the present buildings. The dynamos were made by Johnson and Phillips and are 60 kilowatt sets. And run at 100 volts. The engines are high-speed compound Alley and McLellan enclosed type engines of 76 horse power. Diameter of high pressure cylinder 9 in. Diameter of low pressure cylinder 14in, stroke 8in speed 470 resolutions per minute. The dynamo bearings lubricated by means of rings in oil boxes while the cranks of the engines enclosed in the crank chamber are provided with splash lubrication. The oil in these crank beamers is cooled by means of cold water supplied from the water company’s main. Which after passing through the crank chamber is delivered into the feed water tank?
The engine-room is provided with travelling crane by Carrick and Ritchie capable of lifting 90 tons, so constructed that all the motions can be controlled from the engine room floor level, thus doing away the necessity of monopolising one mans labour. The traveller runs on gantry rails at a height of 23ft. 6in. above the engine-room floor level, and is supported on arches on one side, and on steel stanchions and rolled steel joists on the other. The engine foundations rest on the concrete float and the engine-room floor is composed of girders and concrete. The space around the foundations is thus left clear and all exhaust and drain and other pipes are supported from the engine room floor by means of slings. Arrangements have been made for the installation of condensing plant, which was to havoc been placed in the basement. The basement is drained into a sump fitted with non return valves to prevent any water entering at high tide.
The engines at the present time exhaust into atmosphere two outlets being provided. One at each end of the engine room. The steam for the heaters is taken off one of the outlets, a back pressure valve being provided to automatically keep a pressure of 6 in. to 18 in of water on the exhaust steam in order to force it through the water in the heater trays. Valves are placed in the main exhaust so that some of the engines may be exhausting to atmosphere while others are exhausting to the heaters or to condensers
The output of the station is controlled from a switchboard situated at one end of the engine room on a gallery 14ft above the floor level. The machine panels are on the left hand side, and are separated from the feeder panels on the right by the exciter panel and the synchronising panel. The output from each machine goes direct through two fuses one being on each phase. The other pole of each phase being connected to earth. After passing through these two fuses it goes through a double-pole snitch and through to ammeters on to the bus bars. Energy sent out to the mains is registered on Thomson Houston primary watt meters on the earthed leads. There are at present four in use.
Units generated by the two day load are registered on two 50 ampere TH. primary watt meters which by means of a small auxiliary bus bar are kept independent of the 250 ampere motor which register the output of the larger alternators. They are all connected between the machines and the earthed bus bars, but to ensure absolute safety each is fitted with an isolating plug switch so that they may be inspected or cleaned if necessary without being removed from the switchboard. The normal full load output of the day load sets is 22 ampere, and the larger meters do not come into operation until the current exceeds that amount, so that the sum of the readings of all these meters should represent accurately the total units generated. Each feeder panel carries two ammeters, a double-pole switch, and two single-poles fuses.
The synchronising connections are arranged in duplicate, one synchronising transformer being placed on each phase. The act of synchronising is only performed on one phase, so that the second transformer is merely a standby. The machine switches are so arranged that it is impossible to close any switch until both the plugs energising the synchronising transformers havoc been inserted so that the only machine that can be put into parallel Is the one synchronised. Two other plugs energising the bus bar valves of the synchronising transformers are then inserted on the synchronising panel and a lamp and volt meter are provided in the usual way to give the indications of synchronisation. The machines are first paralleled on the four-pronged plug switch on the synchronising panel and the main alternator switch of the machine thus put in is then closed. It is, in fact, the only own that can be closed. These switches are also fitted with an arc blow-out. Mounted on the machine panels are the necessary rheostats for regulating the fields in the alternators. These, on the day load sets, are arranged so that one makes a slow adjustment - being placed on the shunt of the exciter - while the other, being placed in series with the alternator field makes a rapid adjustment. Those two are so proportioned that the whole of the first is equal to one step of the second. The voltage can by this means be regulated to within half a volt on the lighting network.
The main sets themselves on the other hand are only provided with one rheostat, the second being placed on the exciter panel. Each main set is, of course, provided with the necessary field breaking switch having carbon breaks. The exciter panel controls both exciter sets being provided with a double pole switch and ammeter for each, and a volt meter for the two. There are also mounted on the same panel field regulating rheostats connected up in series with the field of each exciter. Mounted on the synchronising panel are electrostatic volt meters on the bus bars and the machine, and a multicellular electrostatic ammeter by means of which the voltage or current at any substation may be read. This instrument is also provided with a maximum indication register so that the output from any sub-station or any feeder may be recorded automatically.
All the instruments on the switchboard are mounted on marble panels and the panels themselves are carried on a substantial steel L framework. The gallery is composed of steel H girders and concrete. This being covered with ¾ inch of asphalt and then 1 ½ in. of granolithic cement. Thus forming an insulated layer. On this floor are placed rubber mats to give still greater protection to the switchboard attendants. In addltion to these prcautions high tension apparatus is placed at such a height above the ground that it is quite impossible for anyone to touch it accidentally. 1t is also important to note that no metal parts of switches or fuses carrying current can be touched when they are alive, No part of the metal of the switches is alive until the switch is closed and then the contact pieces are buried in the marble of the switch panel.
The provision of a transformer on each phase enables each phase to be tested for synchronisation whenever this becomes necessary after a machine has been disconnected or over hauled thus making certain that the connections are correct.
The area that this company supplies covers 17 square miles and embraces a population of 250,000. The cables which are of the British Insulated Wire Company's manufacture, are of the eccentric type, insulated with impregnated paper, and covered with lead served under hydraulic pressure. The cables were laid on the solid system in earthenware troughs filed in solid with bitumen. They were tested after lying with an alternating pressure of 6000 volts between the conductors, and 2500 volts between the conductors and earth. There are at present eight cables leaving the generating station four on each phase. Those are divided up as follows: - One pair to Westcombe-Hill sub-station, one pair to Concert Hall sub-station, and one pair to Crooms Hill sub-station, the other pair making connection as spare cables to each of the above sub-stations. The output from the station is delivered to the sub-stations at 8000 volts. The outer conductors are in every case connected to the earth bar on the main switchboard. The continuous current district covers the whole of Greenwich. Current is supplied from the generating station at Blackwall Point to two of the substations above referred to at Westcombe Hill and Crooms Hill respectively. Those sub-stations at present contain two motor generators each and supply currant to low tension distributor on the throe-wire system, a voltage of 500 volts being maintained across the outer conductors
At Westcombe Hill sub-station, which supplies Westcombe Park and the district round, there are two motor generators, each consisting of two-phase motor and two continuous current generators, one coupled to each end of the motor. The supply from the generating station is brought by a pair of concentric cables to the high tension switchboard, another pair acting as spare cables for use in emergency. These cables pass directly into fuse plugs and thence trough two double -pole switches. And another set of fuse plugs to the motor armature. The double-pole switches are connected; one to the inners and the other to the outers, thus the circuit can be broken on the outer conductor, which as already stated are connected to earth. The motor is connected up to a resistance in the usual way. The low-tension switchboard possesses no unusual features, but is similar to the dynamo and feeder panels of a continuous current station. Provision is made for the addition of another motor generator at this substation.
At Crooms Hill sub-station, which supplies the district round Greenwich Park, the arrangements are very similar, with the exception that this sub-station is a larger one than that at Westcombe-Hill, and that provision is to be made in the immediate future for the supply of current to the South East Metropolitan Tramway under the Order which they have obtained this session. The plant at present installed is the same size as the plant at Westcombe Hill substation. The low- tension distributors from these two sub-stations are interconnected, so that each can supply the other if necessary.
The system of distribution adopted in the alternating- current area calls for no special mention And only differs from that of an ordinary low-tension alternating network In that the distribution on any one side of a road is always on a different phase to that on the other side, so that two-phase motors may be used in any part of the district. To facilitate balancing the electrostatic ammeters above referred to have been introduced. This apparatus, which for want of a better name we have called an electrostatic ammeter, is a Kelvin electrostatic volt meter, and under normal conditions is used as such, but by means of a separate small transformer, in series with the outer of each of the four cables the our rent going out of each feeder may be ascertained. The secondary of each of these transformers may be connected in turn to the volt meter terminal by ordinary wall plugs, and it will be seen that the electromotive force across the terminals of the secondary windings is proportional to the current passing trough the feeder. These transformers are furnished with three windings, so that readings may always be obtained at the best part of the volt meter scale, but the norma1 position of the transformer switches is such that the smallest of the three readings per ampere is obtained. This is merely a precautionary measure adopted to prevent damage to the instrument in the event of its being left connected all night by mistake.
Each of the sub-stations is connected to the generating station by two or more pilot wires, and as the actual current in the series windings of the series transformers is negligible, they - the pilot wires – are used to show by means of the switchboard multicellular the output in amperes on any feeder in the sub-station., no correction being necessary for C2R 1osses on the pilot wires. The maximum indication register is a simple attachment by wick the maximum output on the feeder during the night is ascertained it consists of a second pointer moved by the volt meter index in one direction only.
The introduction of these series transformers into the substations enables the ampere readings to be very accurately taken on the volt meter, and only the one instrument is necessary for any number of feeders. It will, of course, be clear that the pilot volt meter on the generating station switchboard is ordinarily used to ascertain the volts on the low-tension bus bars of either the direct or alternating sub-stations. The feeders to all the other four sub-stations in the alternating current area are taken from the Concert Hall substation. The low-tension distributors from each sub-station are so planned that three can be connected together at certain points, so that in case of necessity one sub-station can be made to help another.
We observe that the system of supplying the wiring and fittings for six free lights now in operation at the House to House Company, and recently introduced into the South London Company has been adopted, but we are inclined to think that it will be difficult to Induce consumers to extend their six-light installations.
No doubt a great many people who would not otherwise become consumers are tempted by the six free lights but It is doubtful whether, having induced the company to supply at their own expellee the six lights they are most anxious to have, they will be so far convinced of the advantages of electric light that they will at their own expense put in wiring and fitting in any other room in the house. It would appear to us that the effect of this half hearted attempt at free wiring will be to emphasise the peak of the load curve, because most of the six-light installations will come on simultaneously, while at the same time no inducement is offered to the consumer to take electricity for the lamps in passages, basement, and bedroom, which after all are far more remunerative to the supply company.
The Blackheath Company is charging 6d. per unit for lighting, and inasmuch as this is equivalent to gas at 3s per 1000 cubic feet, people who have electric light in their principal rooms will probably be content to use gas at 2s. 8d. the price charged by the local gas company in this kitchen and bedroom, etc etc. This is, however, no doubt a matter in which the company will be guided by practical experience, although we should have thought that at this point in the history of electric supply there should be sufficient experience to indicate the most profitable policy in any district of London. The company's area, embracing as it does such districts as Greenwich, Woolwich, Lewisham, and Charlton should have an enormous field for the supply of power, but the demand must be created by offering electricity at a price wish will compete favourably with gas or steam. If some steps are taken to prevent the overlapping of the power and the lighting loads, there appears to be no reason why electricity for motive power should not be supplied at 11d. per unit. So many cases exist in which current is supplied profitably at 1d. for power purposes or indeed, any long hour Consumers, that there would appear to be no necessity-or shall we say excuse for throwing away opportunities, by offering to supply power at 3d.
The station was designed and carried out under the supervision of Mr. Reginald P. Wilson, to whose courtesy we are indebted for the above detail, and for the drawings we were enabled to reproduce. We may, however, perhaps be able to offer a few criticisms on several points. The size of the chimney appears to be excessive, and the position is such that a very large expenditure has been incurred in providing for the economiser inside the boiler house, and a similar expenditure will be involved again when the extension of the boiler-house is built. There appears to be no reason why the buildings should be set back so far from the wharf front. The foundations depend for their security on piles and could, therefore, have safely been put within a few feet of the water. By this means the cost of the coal conveyors and the actual cost of handling coal with or without coal conveyors would have been reduced, and the condensing arrangements would have been to some extent facilitated.
The fact that the engines do not run condensing we have already alluded to, and Mr. Wilson's view. On the subject of cheap supply to long hour consumers are so familiar to central station engineers and to readers of the electrical journals that it would be useless to us to add anything to what he has already said with a view to inducing the directors to supply power at a reasonable price