Part 5

The Kensington Court installation has been previously quoted as an example of what promises to be one of the most successful methods of distributing a constant supply of electricity through a large area, a description of the station may therefore be interesting. The accompanying elevation, Fig. 25,[5] shows the unpretending design of the building, and the very compact arrangement of the generating machinery and batteries. When the illustration was made the plant consisted of one Willan’s single-crank triple-expansion engine in combination with a Crompton dynamo provided with vertical inverted single magnets, the output being 250 ampères at 140 volts when running at 500 revolutions per minute, the steam pressure being 160 lbs. on the square inch. A complete duplicate plant has already been installed, and three more sets of engines and dynamos are shortly to be erected. The draught from the boiler is led downwards by an underground flue, with the object of economising the very limited space as much as possible. As a rule, the dynamo and accumulators are used in parallel, the current enters and leaves the regulating cells by the same contact, in other words, there is only one switch which serves for charging and discharging the batteries. This switch has nine contacts, so as to give nine degrees of regulation of the light; when the dynamo and accumulators are working together, the lights are parallel with either 41, 42, or 43 cells, according to the amount of charge in the cells and current required, while, when the dynamo is out of circuit, the lights are worked off, 50, 51, 52, or 53 cells. The current passes through the usual measuring instruments, and each main conductor is protected by safety fuses mounted in a Hedges duplex cut-out. The accumulators are of the Planté type, but instead of being plain lead are sawn out of ingots which are cast porous on the Howell process. Each cell contains 35 plates, 8 in. × 8 in., and, as each plate when fully formed is said to be capable of yielding five ampère-hours per pound of lead, the cell has about 600 ampère-hours total capacity. In the event of a serious breakdown the whole of the work would fall on the accumulators, which could furnish a steady current for perhaps an hour or more; and herein lies the novelty of the arrangement. For the first time we have an accumulator put in not only as a fly-wheel to the whole system and to give the advantage of supplying current throughout the day and the small hours when the engine is not running, but also to act as an actual reserve. The routine is as follows:—the dynamo will start charging the accumulators a few hours before dusk; for a short time after lighting hours commence, the dynamo alone will supply sufficient current, but later on the demand will gain on the dynamo, and a certain portion of the discharge will be from the accumulators. At eleven o’clock at night the engine will be stopped and the accumulators will alone supply the demand for the rest of the night. In the small area occupied by the station there is ample room for a plant of six times the present capacity, and it is intended to erect sub-distributing stations at points at the outskirts of the district where accumulators to act as transformers will be fixed, which will be charged by a special main with a current of 500 volts, the outgoing wires from the sub-station taking electricity at the usual E.M.F pressure for incandescent lamps in houses of 100 volts.

[5] From _Industries_.

Thirteen candle lamps are used in the district, having been found to be more convenient than 16 or 20 candle-power, the 13 candle is obtained for 36 watts, or 2·75 watts per candle. The price charged to consumers is 8_d._ per Board of Trade unit, or equivalent to gas at about 4_s._ 7_d._ the 1,000 cubic feet. Meters on the Aron plan, Fig. 17, are used, a card being supplied on which the readings are entered exactly similar to the method adopted with gas. The service mains terminate at the meter, where the company fix for their own purposes a double pole switch of the author’s design, Fig. 26, which enables both wires to be disconnected, a spring shut-off, marked S S, prevents the switch being left partly on.

SYSTEM OF DISTRIBUTION.

The mains from the Kensington Court Station are laid underground in a culvert 18 in. by 12 in., which is built with brickwork and cement under the pavement. A double conductor of flat copper, 0·25 square inches section, is stretched from shackle insulators attached to iron bars, which are firmly built into the culvert; the continuity of the circuit is provided by means of stranded wire, which connects each section; the flat copper rests on the top of porcelain insulators, fixed on vertical iron pieces, which are built into the floor. Connections with the sewers are left for drainage, and six surface boxes are provided for every hundred yards. Where house connections have to be made, the branch wires are united by soldering to the bare copper mains. For crossing under the streets a heavily insulated cable is employed, and is led through cast-iron pipes.

Until a larger amount of mileage is actually at work, it is difficult to express an opinion as to which is the cheapest and most efficient method of laying conductors in the streets. The relative cost of two plans tried at Kensington Court—the insulated and the bare cable in a culvert—was given by Mr. Crompton in the following Tables, No. 1 and No. 2, which are taken from a paper read before the Society of Telegraph Engineers and Electricians on April 12th, 1888.

Table No. 1 refers more particularly to what is known as the Callender-Webber system of using bitumen concrete, which is compressed into blocks or cases usually about 6 ft. long, 8 in. by 5½ in. section, having two-inch holes through which the insulated copper cable is led.

The estimates given in Table No. 2 were criticised by Mr. Kapp, who thought that “a more reliable conductor could be obtained by using a high-class lead-covered cable, which might be laid in the ground with the simple protection of a rough tarred plank to cover it.” The cost of digging the trench and running in the cable from the drum was quoted at 3_s._ a yard, and the total cost, inclusive of £10 for surface boxes, at £155 per 100 yards, instead of £187, as shown by the Table.

TABLE I.

_Cost of Laying 100 Yards of Double Conductor underneath the Footway of a London Street._

+---------+--------+--------+ | Single. | 7/16 | 19/15 | | No. 16. | | | -------------------------------+---------+--------+--------+ Area, square inch | ·0032 | ·0225 | ·0773 | Area, square millimetre | 2·08 | 14·6 | 50 | Weight per 100 yards run lb. | 7½ | 53½ | 183¼ | Cost of copper at 7¾_d._ |£ 0 4 10| 1 14 6| 5 18 0| Cost of insulation | 1 3 2| 4 8 6|11 2 0| +---------+--------+--------+ Total cost of Cables | 1 8 0| 6 3 0|17 0 0| Casing, bitumen, and cement | 5 3 0| 5 5 0| 8 0 0| Labour, Laying | 3 0 0| 4 0 0| 5 0 0| Trenching and repairing | 25 0 0|25 0 0|25 0 0| Surface boxes and connection | 5 0 0| 7 0 0|10 0 0| Engineer and superintendent | 3 0 0| 4 0 0| 5 0 0| +---------+--------+--------+ Total |£42 11 0|51 8 0|70 0 0| Add extra if copper, at | | | | 9½_d._ | 0 1 1| 0 8 0| 1 7 0| +---------+--------+--------+ | 42 12 1|51 16 0|71 7 0| Cost of copper per lb., | | | | laid complete | 5 13 6| 0 19 4| 0 7 9| Current in ampères | 1·2 | 8·1 | 28 | Cost per ampère | 35 10 0| 6 8 0| 2 10 6| -------------------------------+---------+--------+--------+

+--------+---------+ | 19/12 | 19/10 | | | | -------------------------------+--------+---------+ Area, square inches | ·1613 | 0·25 | Area, square millimetres | 104 | 161·25 | Weight per 100 yards run lb. | 392 | 576 | Cost of copper at 7¾_d._ |12 13 0| 18 15 0| Cost of insulation |24 17 0| 35 17 0| +--------+---------+ Total cost of Cables |37 10 0| 54 12 0| Casing, bitumen, and cement |12 10 0| 12 10 0| Labour, Laying | 5 0 0| 6 0 0| Trenching and repairing |25 0 0| 25 0 0| Surface boxes and connection |10 0 0| 10 0 0| Engineer and superintendent | 5 0 0| 6 0 0| +--------+---------+ Total |95 0 0|114 2 0| Add extra if copper, at | | | 9½_d._ | 2 17 0| 3 5 0| +--------+---------+ |97 17 0|117 7 0| Cost of copper per lb., | | | laid complete | 0 5 0| 0 4 1| Current in ampères | 58 | 90 | Cost per ampère | 1 13 9 | 1 6 0| -------------------------------+--------+---------+

+-------------+-------------+ | 37/10 | Two Sets. | | | 37/10 | -------------------------------+-------------+-------------+ Area, square inches | 0·5 | 1·0 | Area, square millimetres | 322 | 645 | Weight per 100 yards run lb. | 1153 | 2306 | Cost of copper at 7¾_d._ | 37 5 0 | 74 10 0 | Cost of insulation | 70 15 0 | 141 10 0 | +-------------+-------------+ Total cost of Cables | 108 0 0 | 216 0 0 | Casing, bitumen, and cement | 16 0 0 | 22 0 0 | Labour, Laying | 10 0 0 | 18 0 0 | Trenching and repairing | 25 0 0 | 25 0 0 | Surface boxes and connection | 10 0 0 | 10 0 0 | Engineer and superintendent | 10 0 0 | 10 0 0 | +-------------+-------------+ Total | 179 0 0 | 301 0 0 | Add extra if copper, at | | | 9½_d._ | 8 10 0 | 17 0 0 | +-------------+-------------+ | 187 10 0 | 318 0 0 | Cost of copper per lb., | | | laid complete | 0 3 3½ | 0 2 8¾ | Current in ampères | 180 | 360 | Cost per ampère | 1 1 0 | 0 17 6 | -------------------------------+-------------+-------------+

+-------------+-------------+ | Four Sets. | Six Sets. | | 37/10 | 37/10 | -------------------------------+-------------+-------------+ Area, square inches | 2·0 | 3·0 | Area, square millimetres | 1290 | 1935 | Weight per 100 yards run lb. | 4612 | 6918 | Cost of copper at 7¾_d._ | 149 0 0 | 224 0 0 | Cost of insulation | 283 0 0 | 424 0 0 | +-------------+-------------+ Total cost of Cables | 432 0 0 | 648 0 0 | Casing, bitumen, and cement | 40 0 0 | 55 0 0 | Labour, Laying | 35 0 0 | 50 0 0 | Trenching and repairing | 30 0 0 | 35 0 0 | Surface boxes and connection | 10 0 0 | 10 0 0 | Engineer and superintendent | 20 0 0 | 25 0 0 | +-------------+-------------+ Total | 567 0 0 | 823 0 0 | Add extra if copper, at | | | 9½_d._ | 34 0 0 | 51 0 0 | +-------------+-------------+ | 601 0 0 | 874 0 0 | Cost of copper per lb., | | | laid complete | 0 2 7¼ | 0 2 6¼ | Current in ampères | 720 | 1,080 | Cost per ampère | 0 16 8 | 0 16 1 | -------------------------------+-------------+-------------+

TABLE II.

_Cost of Laying 100 Yards of Double Conductor of Bare Copper carried on Insulators in a Culvert._

+----------+---------+---------+ Area in square inches | 0·25 | 0·5 | 1·0 | Area in square millimetres | 161·25 | 322·5 | 645 | Weight of copper in lb. | | | | per 100 yards | 576 | 1153 | 2306 | Cost of copper at | | | | 7¾_d._ per lb. | £18 15 0| 37 5 0| 74 10 0| Laying | 9 0 0| 9 12 0| 9 12 0| Insulators | 0 4 6| 0 4 6| 0 4 6| 6 surface boxes and | | | | connections | 10 0 0| 10 0 0| 10 0 0| Culvert, 18 inches × | | | | 12 inches, for | | | | two lines conductor, | | | | in brickwork | 53 8 0| 53 8 0| 53 8 0| and cement, replacing | | | | pavement | | | | Engineers and | | | | superintendence | 6 0 0| 10 0 0| 10 0 0| +----------+---------+---------+ Total | £97 7 6|120 9 6|157 14 6| Extra for copper at | | | | 9½_d._ per lb. | 3 5 0| 8 10 0| 17 0 0| +----------+---------+---------+ Total |£100 12 6|128 19 6|174 14 6| Cost of copper per lb. | | | | laid complete | 42_d._ | 27_d._ | 18·2_d._| Current in ampères | 90 | 180 | 360 | Cost per ampère | 1 2 3| 0 14 5| 0 9 8| ---------------------------+----------+---------+---------+

+---------+---------+------------- Area in square inches | 2·0 | 2·55 | 3·00 Area in square millimetres | 1290 | 1645 | 1935 Weight of copper in lb. | | | per 100 yards | 4612 | 6125 | 6918 Cost of copper at | | | 7¾_d._ per lb. |149 0 0|190 0 0|224 0 0 Laying | 9 15 0| 9 15 0| 10 0 0 Insulators | 0 4 6| 0 4 6| 0 4 6 6 surface boxes and | | | connections | 10 0 0| 10 0 0| 10 0 0 Culvert, 18 inches × | | | 12 inches, for | | | two lines conductor, | | | in brickwork | 53 8 0| 53 8 0| 53 8 0 and cement, | | | replacing pavement | | | Engineers and | | | superintendence | 10 0 0| 10 0 0| 15 0 0 +---------+---------+------------- Total |232 7 6|263 7 6|312 12 6 Extra for copper at | | | 9½_d._ per lb. | 34 0 0| 43 10 0| 51 0 0 +---------+---------+------------- Total |266 7 6|306 7 6|363 12 6 Cost of copper per lb. | | | laid complete | 13·8_d._| 12_d._ | 12 6_d._ Current in ampères | 720 | 910 | 1080 Cost per ampère | 0 7 5| 0 6 9| 0 6 8½ ---------------------------+---------+---------+-------------

THE VIENNA CENTRAL-STATION.

The practical success of the Battery Transformer system has been demonstrated at Vienna, where an installation of five thousand lamps in the Opera House and Burg Theatre was maintained for the past year from a distributing station 1,400 yards away. The boilers are fixed in a basement formed by excavating the court-yard of a private house to a depth of 15 feet 6 in. below the street level; the building itself is utilised partly for offices and partly as a large dynamo and engine-room. Each dynamo is designed to give an output of 72 kilowatts or 120 ampères, at 600 volts pressure. The current is led by means of a lead-covered cable underground to the accumulators, which are erected in groups of 52 cells each, so as to give 100 volts to the lamps, with a comfortable margin. The total pressure required to charge the four groups of batteries in series varies from 430 volts at the time the batteries are giving off work, to 480 volts for the short time during which the charge is being completed. During five hours of lighting about two-thirds of the current comes direct from the dynamos; but during this time, for short periods, the demand for current often increases to such an extent that these proportions may be reversed, and the batteries supply two-thirds of the total.

The regulation of groups of batteries placed in series is not a difficult matter, and will be understood by referring to the following diagram, Fig. 27:—

The four battery stations mentioned as arranged in series are represented. The current may be supposed to enter at the right hand corner, passing through the first battery with the lamps parallel to it, and from that battery to the commencement of the next, and so on through the third and fourth, the current being varied at will at the central-station, or kept constant by means of an electrical governor. The potential for each of the four groups of lamps is maintained in the following manner:—In each group one terminal is kept permanently connected to one of the discharge mains and to one of the charging mains; the other terminal can be shifted from cell to cell according to the E. M. F. required in the corresponding lamp circuit by means of a contact regulator. This movable terminal is shown by the bunch of lines at one extremity of each battery group. The rule for charge and discharge is, that the terminal cell at the regulating end of the battery is so arranged that it neither receives nor gives off current, so that there is no loss of energy in the shape of E. M. F. The contact regulator, which was designed by Mr. Crompton for use at Kensington Court, is shown by Fig. 28:—

The ring contacts are arranged in a line in such a manner that a circular contact-piece, made of thin sheets of copper, can be forced through them in turn by means of a central screw spindle. The mains for charge and discharge are attached to the fixed disc contacts on the central screws, and the regulating cells of the battery are coupled to their respective contact rings by sockets at the back of the board.

The difficulty with the battery transformer system is the introduction of 400 to 500 volts into the houses, which would be necessary without the batteries are always fixed in sub-stations from which a low-pressure current, say of 100 volts E. M. F., could only be distributed.

A method has been devised by Mr. Henry Edmunds to obviate this disadvantage. He also uses the high-tension current to charge the batteries, but by means of a distributor, which is automatically worked by the current, each group of cells is charged in turn, when it is entirely cut off from the supply main to the house, through which current is perhaps being taken for lighting purposes. The system is now being adopted by the Cadogan Electricity Supply Company, Chelsea.

DIRECT-CURRENT TRANSFORMERS OR DYNAMOTORS.

The method of transforming by direct current without the aid of batteries is not practically at work; but, as the advantages are so obvious and its development is only a question of time, a description of the system may not be considered out of place.

The electrical exhibition at Philadelphia in 1884 contained a dynamotor which was exhibited by the Van de Poele Electric-Light Company, but, as far as could be ascertained, was not worked, and, as it was simply described as an induction machine for distributing currents for the use of incandescent and other lights, it attracted little attention.

The advantages of an alternating current transformer system of distribution, Class II., has been put forward in these pages, especially that of simplicity and cheapness. An alternating current dynamo for a given output is cheaper than a direct, and it takes less labour to look after it, because it has no commutator.

An alternating transformer is also an exceedingly simple piece of apparatus. If originally made with due care and kept in a dry place, it never breaks down, as it has no moving parts, and so there is nothing to go wrong.

The alternating system of distribution has, however, some very serious disadvantages. In the first place, it is most important that motors should be driven during the day when the lights are not in use. In the second, batteries cannot be used in an alternating current system, so any immunity from breakdown that they might ensure is wanting; and steam must be kept up all day and all night.

If motors are wanted during the day, so that the load on the engine is nearly constant, batteries are not so valuable, except with a view of preventing a breakdown; but, if batteries cannot be used, the advantage of using motors becomes enormous, as the plant has to be large enough to supply the maximum load, and would otherwise be idle during the day.

In alternating current systems there are two difficulties in the way of using motors. It is difficult to make an alternating current motor that will start, and, if that difficulty is surmounted, it is difficult to make an alternating current motor that will work on varying loads without great waste of power. The question of the efficiency of alternating current motors has never been really practically studied yet; and, until these difficulties are overcome, we must regard alternating current motors as non-existent. Several methods of working alternating current transformers off direct currents by commutating the primary have been proposed at different times; but they all seem to be impracticable, and it seems impossible to get over the difficulties that arise from sparking when it is attempted to break a high-tension circuit.