— – Long-distance Transmissions.—The first real long-distance electric power transmission was carried out by Marcel Deprez at the Munich Exposition of 1882, with two Gramme machines as motor and generator. These were placed respectively at Nunich and at Miesbach, a distance apart of 57 kilometres (37 miles). They were connected by an ordinary iron tele graph wire, 41 mai. in diameter, and constituted a complete metallic circuit of 114 kilo metres (74 miles) in length. The resistance of the line measured 950.2 ohms; that of the generating machine at Miesbach. .J50-4 ohms; and that of the motor at Munich, Speed of generator at Miosbach 1,611 revolutions.
Intensity of current at Miesbach 0'519 ampere.
Speed of motor at Munich 752 revolutions.
Difference of potential at terminals of motor 850 volts.
Work measured by brake at motor 0.25 II. P.
From these data the following values were calculated : Difference of potential at terminals of generator 1,343 volts.
Total electrical energy at Miesbach 1•13 II. P.
Total electrical energy at Munich 0433 II. P.
Electrical efficiency per cent.
It will be, understood here that this efficiency is not the absolute or commercial efficiency, but the electrical alone.
These were followed by other experiments, but probably the most important of M. Deprez's transmissions was that undertaken by hint in 1385 between Paris and Creil, a distance of 34 miles. The line consisted of a lead-encased insulated copper wire, 5 mm. in diameter, and its resistance was 100 ohms. The generating machine was situated at Creil. It had two rings revolving in two distinct magnetic fields, each composed of eight eleetro-magnets. Each armature had a resistance of ohms. The current produced by this machine was utilized at La Chapelle, near Paris, by two receiving machines, situated at some hundreds of metres from each other. Each possessed, like the generator described, two rings ; they were each of metre in exterior diameter and had an electric resistance of 18 ohms. In a note presented to the French Academy of Sciences, M. Deprez gave the results of experi ments undertaken with these machines, and they are quoted below: First E.iperiment.
General or. Receiver.
Speed in revolutions per minute190 248 Electromotive force, direct or inverse 5.469 volts. 4,242 volts.
Intensity of current amp. 7 21 amp.
Work in field magnets (in horse-power) Electrical work (in horse-power) Mechanical work measured with the dynamometer or the brake (horse-power) 35.10
In October, 1887, a committee of experts carried out a series of tests on the electrical transmission plant between Kriegstetten and Solothurn, Switzerland. At Kriegstetten, there is a water-power available, representing about forty actual horse-power, and the prob lem was to carry as much of this power as possible to a mill in Solothurn, the distance being 5 miles. There are at Kriegstetten two generating dynamos, and at Solothurn two motors, coupled up on the three-wire system. Each dynamo weighs 3 tons 12 cwt.. and has a Gramme armature 20 in. in diameter and 14 in. long, the normal speed being 700 revolutions per minute. The following tables give the results of these tests : A. L. Rohrer, of the Thomson-Houston Electric Co., has applied a plan for a large power plant by which 5.000 horse-power is being transmitted a distance of twelve miles. The diagram, Fig. 2. shows the arrangement. By this arrangement, the generators are coupled mechanically in pairs as one unit on one shaft driven by one turbine, and elec trically the armatures of each unit are connected in series. Each armature has a potential of 2,500 volts. This gives 5,000 volts for each unit at the generating station. The genera tors are separately excited, and have also series windings, which compensate for the loss in the line. At the receiving station there are the same number of units, each consisting of two similar machines, with their armatures in series. and their fields separately excited, but without series winding. Each receiving unit is coupled to the same shaft in the same manner as the generating unit. At the generating station exciters are only used for charg ing the fields, while at the receiving station exciters are used in connection with a small storage battery which is necessary to start the first unit. The mechanically and electrically coupled units at the generating station are united electrically in parallel in one system, by an equalizing bar, as shown in the diagram. It seems advisable to leave the storage battery in the circuit permanently, to keep the fields of the motors fully ex cited, in case the speed should drop. In another instance, 250 horse-power is transmitted a distance of 10 miles with single series-wound units. Each ma chine is wound for a potential of 3.000 volts, and for this purpose a special commutator with 798 segments was con structed.