978 THE COLLIERY GUARDIAN November 12, 1915. were hardly of the size, location, or dignity to do justice to the Pennsylvania railroad. So it is that the three piers now in use have been willed to the Pennsylvania by companies which are its subsidiaries. However, this state of things is now about to be altered. For several years the Pennsylvania railroad has been talking about building coal piers that would give it capacity to handle about any size or condition of coal shipment that might come its way for transference from the Baltimore harbour. Now the piers are almost an accomplished fact, for excavation of land in the section of Baltimore known as Canton has already been started, and the Maryland Dredging Company is doing its contract part to get ready for the 1,000,000 dols. coal piers that have been awarded to Arthur McMullen, of New York, to build. Several sets of plans were drafted for this new structure before all was in order to go ahead. The present plan calls for a pier 942 ft. in length and 66 ft. wide, and with a depth of 30 ft. at mean low tide. The system to be used in carriage of the coal from the cars to the holds is the result of years of research by the engineers of the Pennsylvania, who have adopted a plan of dumping similar to that used by this railroad at Erie, Pa.; and the coal from this will be received in a hopper that will feed into smaller car units of about four tons each. An automatic cable device will be used to carry the coal from these units to the chutes that take the coal to the holds of the vessels. It is expected that these piers will be completed and ready for use late in the fall of 1916. But the Penn- sylvania railroad has three coal piers in active use at the present time. These three piers are known as South Clinton Street—or the Canton Piers—and the Boston Street Piers Nos. 3 and 4. The Canton piers were purchased from the Baker Whitely Coal Company in 1903. They are 48 ft. wide and 780 ft. long, are equipped with two tracks of a capacity of 60 cars, and a chute system of delivering the coal into bunkers. The Boston Street piers are used for local anthracite trade. No. 3 is 50 ft. wide, with a length of 400 ft., and has three tracks of equipment and capacity on top of 30 cars. No. 4 has a length of 400 ft., and is 105 ft. wide, with a top capacity of 55 cars. Both of these piers use a gravity system for placing cars over the chutes. They are also equipped with pockets for the storage of coal, and these are leased to local retailers, who utilise them for harbour delivery and delivery to river boats. South Wales Institute of Engineers. — A meeting of the Institution of Mechanical Engineers, to which members of the South Wales Institute of Engineers were invited, was held at the Institute, Park-place, Cardiff, yesterday (Thursday), when Dr. Dugald Clerk, F.R.S., lectured on “ The World’s Supplies of Fuel and Motive Power.” The attention of the members was drawn to the fact that the Munitions Inventions Department, recently constituted by the Minister of Munitions, for the purpose of dealing with ideas, suggestions and inventions for appliances in connec- tion with the prosecution of warfare on land, has been authorised by him to receive projects of this nature or any matters appertaining thereto. An advisory panel of scientific and other experts, appointed by the Minister, is assisting the Department in the task of dealing with the large number of inventions that have been and are being received, every one of which is given consideration by the panel. This body is glad to consider also suggestions with regard to simplifica- tion and improvements either in the manufacture or in the materials of existing munitions, or indeed in any other respect. Coal Contracts in War Time. — At the Watford County Court, before his Honour Judge Ringwood, the case of Simpson v. Wallace Spiers and Company was considered. The plaintiff claimed from Messrs. Wallace Spiers and Company damages for breach of contract and loss of com- mission and connection respecting coal supplied to Benskin’s Coal Club, of which he acted as secretary. Mr. S. J. Ellis, for the plaintiff, said that the claim of .£65 was for breach of contract on the part of the defendant to supply coal to the plaintiff for the purpose of his coal club. Plaintiff’s practice had been to get one large contract for coal at a reduced price, and sell to his members, charging only a commission for his trouble. In consequence of his failure to carry out the contract, plaintiff practically lost the whole of his connection, and the club had broken up.—Mr. Cairns, for defendants, said that the damage was what it would cost the plaintiff to buy if defendants refused to supply. The point against the plaintiff was that he had been can- vassing for other members and getting outsiders.—Mr. Ellis said that what defendants appeared to rely on was the war portion of the strike clause. On January 29 the defendants wrote regretting that they would have to restrict supplies owing to the enhanced cost of coal, and to the nation being at war, though they were aware of this when they entered into the contract. Defendants said they would be willing to make deliveries at 27s. 6d. a ton. Ezra T. Wilks, giving evidence for defendants, said in making a new contract it was a custom for an approximate quantity to be mentioned if the contract was a continuing contract. They always looked back to see the quantity supplied. Any excess quantity would be charged at extra rates. He did not know whether there was any right of claim to restrict the supply to any dealer. Such a case had never arisen. If a dealer was attempting to get more than his usual quantity the supply was stopped. There was not a colliery in the country able to fulfil its contracts now. The purchaser would have ■to be bound by the custom if he could not get his coal. He would not be entitled to damages if he did not get it.— Charles F. Pearson, secretary of the defendant company, said that they supplied plaintiff with coal since September 1913. The original estimate was for 150 tons for the 8 months September to April.—Mr. Cairns, addressing his Honour, said that under the contract, plaintiff was entitled to something under 20 tons a month. The claim advanced regarding the extra 100 tons was grossly exaggerated. He contended that he was released from liability under the contract owing to the operation of unusual conditions, and the conditions of the country.—His Honour summed up at length on the points raised, and said Mr. Simpson ought to have accepted the terms offered him in the early part of the year. The defendants were entitled to judgment, which he gave for them, with costs. THE FLOW OF ENERGY THROUGH TRANSMISSION LINES.* By Robert A. Philip, M.A.I.E.E. The flow of a material fluid, such as water or air, through the pipes which transmit it may be shown as a ribbon whose varying width represents the variations of current. A similar picture may be drawn of the trans- mission of power. It is, however, more exact to consider that it is energy rather than power which is being transmitted. In the distribution of energy as in the distribution of a material fluid, the total quantity supplied to the distributing system, plus or minus storage in the system itself, must at every instant equal the quantity delivered, including leakage. This funda- mental similarity allows a distribution of energy to be pictured as though it was a distribution of matter. Fig. 1 shows energy transmitted thermally from a steam boiler through a steam pipe to an engine, thence SCALES Electrical ?—-----------gy’..,.-*.?*’ kw. Mechanical H p Thermal ?«■■■»■ B.T.U. per min. / Kilowatt ’ // Horsepower / Horse Power - 424 87 U per mm In to Moron Out or Bourn Motor BO 2 * o I . I Engine 03 $ oo {Electrical Units 834 Mechanical Units I/IO .Thermal Units 47/00 l?O HO too Kilowatts 160 Horse Power 139 126 185 168 7800 8.7u per mm. £ * POWER LOST | | Generator Wires Fig. 1.—Thermal, Mechanical and Electrical Transmission. mechanically through a belt to a dynamo, and finally electrically to a motor. The diminution of 'the stream of energy is indicated as due to separate thermal and mechanical losses of transformation in the engine, mechanical losses in the belt, combined mechanical and electrical losses of transformation in the dynamo, and electrical losses in the wires. This picture may be extended by tracing each branch forward or back to its furthest ascertainable end, and it may be amplified by analysing the losses into more elementary streams and by tracing the flow in greater detail; showing, say, the flow of energy through the reciprocating parts of the engine on its way from the steam pipe to the belt. While this is a general method of picturing the trans- mission of power, it is especially useful in illustrating the meaning of terms used in electrical power transmis- sion by alternating currents, such as wattless current, synchronous condenser and induction generator, there- fore the electrical use of the method will be chosen for amplification, although it will be indicated that the same things may be found in mechanical transmission. In fig. 2 the varying widths and directions of the ribbon of energy flow show the operating characteristics of generators and motors. The width of the outgoing energy stream is, of course, exactly proportional to the load, but is electrical power from a generator and mechanical power from a motor. The efficiency is equal to the outflow divided by the inflow. The illustration shows clearly one important point : the efficiency increases from no load to full load, not because of a decrease in losses, but in spite of an increase in losses. The series illustrates the meaning of the terms generator and motor. They describe, not the construc- tion of an electric machine, but the two ways of using it. The electric machine is reversible in function. It is a generator only so long as the outflowing energy is electrical, and a motor so long as it is mechanical. When it is known whether a machine is operating as a generator or as a motor, two elements of the ribbon picture have been determined. First, which way the arrows of flow should point, and second, as a conse- quence of this, which way the main flow tapers off. While a current of energy may be transmitted by using a current of water or a current of electricity, the energy itself is neither water nor electricity. The water or electricity is but a medium of transmission. Similarly the motion which constitutes the flow of the water or other mediums is not the motion which constitutes the flow of energy. The medium may be, and often is, used over and over again. In fact, the direction in which the belt, water or electricity moves can be reversed without reversing the direction in which energy is transmitted, or vice versa. Therefore, if energy is transmitted by a flow of water or of electricity, a picture of the flow of energy will not be at all identical with a picture of the flow of the transmitting medium, even though the same principles may be used in representing each kind of flow. It will be understood that a repre- sentation of a flow of electrical energy is not at all a representation of a flow of electricity. That the motion of energy and the motion of the transmitting medium are practically independent is also shown by the fact that shafts, belts, water, and * From a paper read at the joint meeting of the Chicago Section of American Institute of Electrical Engineers and the Western Society of Engineers. electricity may be in active motion and yet transmit no power, and that the same mediums may transmit more power at times when they move slowly than when they move rapidly. This is because the mediums transmit no power unless they move under pressure or tension. Power, whether mechanical or electrical, is considered as consisting of two equally important components, one of motion and one of pressure. The amount of power is the product of the two components. For hydraulic transmission the power in foot pounds per second is the product of the flow in cubic feet of water per second by the pressure in pounds per square foot, and similarly, for electric transmission, the power in watts is the pror duct of the current of electricity in amperes by the electrical pressure (potential) in volts. Where power is transmitted mechanically by shafts, belts, or fluids, or electrically by direct currents, the motion and pressure each has its own fixed direction. However, power is also transmitted both mechanically and electrically by motions and pressures which alternate in direction periodically. The pistons, piston rods, con- necting rods, and other reciprocating parts of a steam engine transmit mechanical power in virtue of the:r motion, although this motion alternates in direction instead of being uniformly forward. In these cases it is important to note that the pressure as well as the motion also alternates. The pressure is on one side of the piston on the forward stroke, and on the other side on the backward stroke. Energy is the product of motion and pressure; there- fore, if motion and pressure both reverse, the flow of energy is not reversed, on the principle that the product of two negatives makes a positive. The reversal of the motion of the reciprocating parts of a steam engine does not reverse the motion of the energy which flows forward from steam pipe to shaft during the backward as well as forward stroke. With uniform motion or flow the amount of energy transmitted is equal to the product of the motion by the pressure. The same formula holds for reciprocating motion and alternating flow, provided it understood that by motion and pressure is meant mean motion and mean pressure. The mean is found by squaring the instantaneous values of the quantities averaging these squares over a complete cycle and extracting the square root. The transmission of power by electric current which alternates in direction follows the same principle as the transmission by reciprocating mechanical motion, namely, the reversal of the direction of the electric current does not reverse the flow of energy, because the pressure is simultaneously reversed. An alternating current of electricity, or of water for that matter, will transmit just the same amount of power as a direct current of the same mean magnitude, at the same mean pressure, provided, however, that the current and potential reverse at exactly the same time. Engrne Direct Current Generator FULL LOAD Efficiency 327, HALF LOAD * Efficiency 30% £ * £ O -J J NO LOAD Efficiency 0% ----------------------Electrical Power reverses here----------------— Mechanical Power reverses here — —— — — — — ——~ — - HALF LOAD Efficiency 90% NO LOAD Efficiency 0% SB J: O * <1 FULL LOAD Efficiency 92% Motor Battery Fig. 2.—Direct-current Generator and Motor Operation at Varying Loads. When the motion and pressure reverse simultaneously they are said to be in phase. Alternating motions or currents when in phase with their corresponding alternat- ing pressures are practically equivalent to uniform motions or direct currents for the transmission of power. Under these conditions the ribbon picture of power may be used for alternating current transmission. However, it is to be remembered that the flow represented is not the instantaneous flow, which fluctuates, but the mean flow over one or more complete cycles. It may happen that while the motion and pressure are both reciprocating or alternating, and at the same rate, they fail to reverse simultaneously. When motion and pressure reverse a quarter of a cycle apart any further change in either direction brings the times of reversal closer together. For example, two cranks on the same shaft have their respective dead points as far apart as possible when set, like the cranks of a loco- motive, a quarter of a revolution apart. Motion and pressure are then said to be in quadrature, and each reverses when the other is at a maximum.