WHY MUNICIPALITIES FAVOUR ELECTRICS.
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Experience in Urban Districts. Forms of Charging Switchboards:
IN SEVERAL TOWNS, electrically propelled vehicles are employed for dealing with the refuse. In Sheffield, Wolverhampton, Croydon, and Pontypridd, amongst others, the carts which collect the refuse from door to door arid transport it to the destructor, or to the tip, are driven by electric motors taking their current frpm secumulators carried 1-,y the vehicle. In several cases, tipping arrangements are fitted to the vehicles, worked by the electric motor which drives the vehicle ; and it need hardly be said what a great convenience this is.
in Pontypridd the use of electrically driven vehicles saved the situation when, during the war, the deficiency in local haulage made it impossible to get the refuse collected. It will be remembered that Pontypridd is situated among the hills; one has to go up hill in every direction out of the town. It is heavy upon horse haulage, at any time, and, as horses were commandeered so freely during the war, the situation became very serious. Another important use that has been made of electric. vehicles by municipalities is the conveyance of stores of all kinds about the town ; repairing materials for the tramway for instance, and for the electric light and power main.
Li Croydon, a 3-ton water wagon is driven by electricity, and is found very convenient.
There, also, a 4-ton electric coal wagon, with an electrically-worked tipping arrangement, the current supplied by Edison batteries, has been employed for the past three years (except when off for repairs for a-short period) for carrying coal from East Croydon railway station to the electricity generating station. The wagon makes seven double journeys per day, the double journey totalling two and a half miles of road travel. Thirty tons of coal are handled by it in a, day. For the year ended March, 1918, the tonnage carted was 8,183 at a. total cost of £501, or 14.7d. per ton. The ruling price for horse haulage at that time was 26d.. per ton ; so that a net saving of £325 was made during the year by the employment of the electrically-propelled vehicle in place of horse haulage.
At Wolverhampton, the economy obtained by the use of electrically-propelled vehicles has enabled the electrical department to make an offer of 1s. a ton for handling material by means of electric vehicles, as against very much higher prices demanded in the district for horse haulage.
At Sheffield, the electrically-propelled vehicles employed by the cleansing department are charged partly from the mains of the electricity department and partly from a generator driven by a steam engine, the boiler for which is fired from the refuse destructor, so that a double economy is obtained. The refuse is itself handled economically by the electric vehicles and, in its turn, it furnishes the heat that is converted into electricity at the refuse destructor generating station for recharging the batteries of the vehicles. When the vehicles are charged from the electricity supply service, current is supplied to the cleansing department at 1.1d. per unit, and it is found that 1.59 units are required per mile travelled by the vehicles.
At Croydon, another important use that is made of electrically-driven vehicles is to enable the municipal staff to get about the district. A two-seater Cal" is kept for the use of the staff, and, in it, the mains superintendent is enabled to get about very quiddy to any part of the district; and those who have had to do with town mains, the cables fixed under the street, etc., will appreciate how important this is. A fault is taken in hand very much more promptly, when the mains superintendent can get to the seat of the trouble at once and make his tests and his diagnosis quickly. The staff car has completed five years of service and has run, on an average, 20 miles a day.
The maximum mileage obtained in the staff car, on one charge was 45, and the running cost 1.86d. per mile, made up of :— Repairs and maintenance for this car amounted to 4.32d. per mile, made up of • New _spring for front axle. 0.12d.
Repairs to upholstery ... 0.24d.
Insurance and licence 0.41d.
Interest and depreciation
The cost per ton 14.7d. mentioned above, at Croydon, for handling the refuse, is made up as follows:—
Standing charges Repairs and maintenance ... . 2.78d.
Electrical energy at 1d. per unit ... 1.12d.
Wages (driving and loading coal) 6.20d.
Arrangements for Charging the Battery.
In all cases the batteries are charged at night, between 11 p.m. and 6 ,a.m..; but, also, in nearly all cases, the vehicles come in to the garage or the generating station for a boosting charge during the dinner hour. It will be remembered that, where a generating station is supplying power, the demand is generally decreased during the dinner hour while the generators have to continue running, and the staff at the generating station have to be as much in evidence as during any other part of the day. The boosting charge enables the vehicles to got over a great deal more work than they otherwise would do.
One rule in connection. with all electrical accumulators is, the more frequently the batteries are fed with current, the better are the results obtained from them. The very best results are obtained when the batteries are " floating" as it is termed; when they are constantly receiving current, and constantly delivering current ; as in the case of the large generating stations referred to in the earlier parts of this article, and in the case where they are used for the lighting and starting of motorcars. _
046 At Croydon, there is a very interesting arrangement for boosting charges at mid-day. There is a swinging arm attached to the frontage of the garage building,: to which is attached a standard charging plug. The chief electrical engineer reports that there is quite a regular demand on this source by delivery vans fromand returning to London, calling for the mid-clay boost.
The Conversion of the Current.
The conversion of the current, from the form in, which it is generated to that required by the bate teries, is an important matter. Batteries require
continuous current, and those employed in self-proa pelled vehicles require a prersure ranging from 95 to 115 volts, usually. It is not good practice to employ batteries in electrical vehitles at the usual pressures at which currents are delivered in towns for lighting purposes, viz., at 200 to 260 volts. The battery requires from 10 per cent. up to :30 per cent. additional voltage above that which it will furnish when discharging. Lead cells that give from 2 volts downware.; on discharge, require from 2.2 volts up to 2.5 volts, and sometimes to 2.75 volts when being charged, and provision has to be made for giaing the current to the batteries at these pressures, daring the night. charge at any rate. The boosting charge can be put in at anything from 2.2 volts to 2.5 volts, according to the state of the batteries. It must always he above t%e back pressure which the battery immediately commence-3 to furnish directly a Current passes through it.
On the other hand, the current available at the "bus bars" of most modern electricity generatiraif stations is three-phase alternating and often at 6.000 volts. The latth bars of a, generatng station practically form the clearing house of the station. The currents from all generators, excerpt those detailed for special work, are brought to the bus bars, and all currents, for all purposes, almost without exception, are taken from the bus bars. The high pressure has to be transfoarned down to one that is convenient for use in motor gewrators, or retary converters, and then it has to be converted from alternating to continuous currents. Every conversion makes a charge upon the current, just as a steam engine, for instance, makes a charge upon the indicated horse power delivered by its piston, for overcoming its own friction. The number of units actually taken front the bus bars of any generating station, to furnish each unit delivered to the batteries being charged, may easily be double the number taken in by the battery.
Charging Switchboards.
Various forms of switchboards have been designed to enable the requirements to be met during the charging period, but most generating stations appear to have adopted that which has been brought out by the Igranic Electric Co., specially for the purpose. The Igranic Co. are specialists in electrical controlling devices, and one of their charging switchboards is shown in one of the illustrations accompanying this article. There is an upright steel frame arranged to stand alone, on its own base, and to the front of the frame the separate charging panels, or sections, are fixed. It consists of a slate base 24 ins, wide by 10 ins. high ; this is the usual insulating base for lowpressure installations. Upon the slate base, all the apparatus required for charging is held. This includes two fuses to guard against too powerful currents flowing into the battery and an electro-magnetic automatic out-out, to prevent the battery discharging through the charging dynamo as it would do if the pressure of the latter was reduced below that of the accumulator at the moment.
As will be seen from the illustration, a meter is carried on a swinging bracket attached to the upright framework. The meter is what is known as a duplex instrument ; one-half of it shows the amperes going into the battery, and the other half the voltage of the charging current It is practically an ampere-meter and a voltmeter in one ease. The ampere-meter is arranged to show if the battery is discharging through the charging dynamo. There is a pilot lamp, which lights up immediately a battery is connected to the ch a rging service.
On the right of the charging panel will be noticed a switch, with a very strong handle ; the switch has three positions—" open," "closed," and " meter readipg." When it is on the" open" position the ourrent is cut off frOm the battery ; when it is on the closed position the current flows through the battery ; and, when it is forced to the third position against a spring arranged to oppose its motion into this position, that panel is connected to the meter and the currents and pressure can be read off.
Normally, the switch is either on the open or clesed position ; always en the " closed " position after charging has commenced, until it is complete, or it is desired to disconnect the battery for any cause, or if the pressure of the charging service fails.
, In the body of the panel will be noticed two sets of contacts, with a rod between them, and also a bridge 'with an insulating handle, that can be moved over the contacts. The two series of contacts, with the bridge, form an adjustable resistance, by means of which the pressure at which the current is flowing into the battery can be varied. When the battery is first connected, the whole available resistance is inserted in the circuit and it is not possible to close the automatic cut-out on the left, which is shown with an insulating handle, unless all available resistance is inserted. As the charging proceeds and higher pressures are required, to overcome the higher back pressures being furnished by the battery, resistance is cut out by moving the bridge to the right.
The charging panels are made in two sizes, one to handle currents up to 90 amperes, and the other up to 180 amperes. Practically any number of charging panels can be assembled. Each upright frame is ar ranged to take eight panels. Frames can be fixed together, side by side, each carrying its own quantum of panels and, in that way, a charging switchboard capable of dealing with any number of vehicles can be built up. The arrangement is very similar to that employed with modern high-tension switchboards, where separate enclosed steel cells are built together into a switchboard, as large as may be required.
The Igranic Co. have arranged their panel charging boards for different conditions that may arise. Panels may be set apart upon one or more of the frames, for dealing with the currents of two-phase, or three-phase motor generator sets, and any other conditions that may have to be dealt with. In certain cases, one or more panels are arranged for discharging the accumulators. It sometimes happens, when an accumulator is badly sulphated, that it has to be charged and discharged, two or three times before it is brought into working condition again ; the arrangement mentioned provides for this.
Where the Igranic charging panels are employed, the whole arrangement is very simple. When a vehicle comes into the garage, or the yard, the charging flexible cord is plugged into the vehicle and into its place in the charging panel, and the rest is as described above.
The writer begs to thank the following gentlemen for the information that they'ha.ve kindly given him, with reference to the work that has been done in connection with the electrical departments under their control :—Mr. Alec. C. Cramb, Borough Electrical Engineer, Croydon; Mr. Sydney T. Allen, Chief Engineer and General Manager, Wolverhampton ; Mr. J. E. Teasdel, Engineer and Manager, Pontypridd ; Mr. S. E. Fedden, General Manager and Engineer, Sheffield; Mr. J. A. Priestley, Superintendent Cleansing Department, Sheffield. He has also to thank Mr. Cramb, Mr. Alien, and Mr. Teasdel for the use of the photos from which the illustrations are produced.