November 26, 1915. THE COLLIERY GUARDIAN. 1083 mately equal product, consisting of a different motion and a correspondingly different pressure. Where both motions and pressures are mechanical the transforming device is called gearing, where one pair is mechanical and the other electrical it is called a motor or generator, and if both are electrical it is called a transformer. While energy flow and magnetising flow can be con- sidered to exist in the same circuit practically inde- pendently, there are not two distinguishable currents of electricity in the same wire. The currents and pressure of energy flow and of magnetising flow combine into a single current and pressure. However, on com- paring the composite current with the composite pressure it is found that the times of reversal are no longer either simultaneous or in quadrature. The product of current and pressure is power, the kind of power depending upon the phase. Disregarding the phase, which is often unknown, the product is called apparent power. When the phase of the two quantities is the same the apparent power is the same as energy flow; when phases are in quadrature it is the 490KVA MAGNETIZING FLOW m?iTVA KI 75KVA FilWnWI Mlllllllil IOO KW I00K.W iOOKW I00KW IOOKW IOOKW IOOKW tQOKW. I00KW IOOKW ENERGY FLOW 100% PF 90 80 70 60 50 40 30 20 !0%PF Fig. 7.—Ratio of Magnetising Flow to Energy Flow at Different Power Factors. same as magnetising flow. Tor intermediate phases apparent power consists of an energy flow component, and a magnetising flow component. It is found that the square of the apparent power is equal to the sum of the squares of the energy flow and the magnetising flow. This leads to the conclusion that if the ribbons representing energy flow are laid, say horizontally, and those representing magnetising flow are turned verti- cally, then a diagonal ribbon connecting them will represent the apparent power. While apparent power is not itself a fundamental kind of power, it is, perhaps, more readily measured than either energy flow or magnetising flow, as it is only necessary to measure the current by an ammeter, and the pressure by a voltmeter, and multiply the result, without regard to the difference in phase. It is also of importance, because furnishing a measure of the size of generators, transformers, motors, etc., which must be used to transmit simultaneously the flow of energy and of magnetisation. . Power factor expresses the relation between energy flow and apparent power. It is the number of kilowatts of power delivered per kilovolt-ampere apparently trans- mitted. Fig. 7 shows the relation between the flow of energy and the flow of magnetisation at various power factors. The two flows are equal for a power factor of l/v/2= 71 per cent. With increasing power factors the proportion of magnetising flow diminishes until it Synchronous Pump Exciter Motor Under Excited lagging Current Synchronous Pump Exciter Motor Over Excited Leading Current Alternating Engine Exciter Generator Under Excited Fig. 8.—Directions of Flows with Leading and Alternating Engine Exciter Generator Over Excited lagging Lagging Currents. vanishes at unity power factor, while with decreasing power factors the proportion of energy flow diminishes, and it becomes zero at zero power factor. While the magnetising power is relatively less at low than at high power factors, an increase in power does not necessarily mean that the magnetising power has decreased. Thus, in an induction motor, the power factor is higher at full load that at no load, nevertheless, the magnetising power is also greater. The increased power factor results from a great increase in energy flow accompanied by a small increase in magnetising power. The terms “lagging” and “leading” indicate the rela- tive directions of flow of the two kinds of power. If they flow in the same direction the current is said to be lagging, if in opposite directions, leading. If the current is lagging it may be changed to leading by reversing either, but not both of the flows. If a synchronous motor is under-excited the current is lagging. Increasing the excitation makes the current leading, because it reverses the flow of magnetisation, while the flow of energy is not affected. If, however, the excitation is not increased, but mechanical power is applied to drive the motor as a generator, the current also becomes lead- ing because the flow of energy has been reversed while the flow of magnetisation is not changed. If the excita- tion is increased, and mechanical driving power is also applied, the current remains lagging because both flows have been reversed. These effects are shown in fig. 8. Where a circuit branches, say, from one generator to two motors operating at different power factors, the determination of the power factor of the generator from that of the motors looks rather complicated. The same problem is extremely simple, if viewed as the division of two kinds of currents each into two branches. Fig. 9 shows that this complicated relation of power factors is merely a roundabout way of saying that the induction motor takes 60 k.v.a. of magnetising power, while the synchronous motor gives out 20 k.v.a.; therefore the generator must give out the difference, or 40 k.v.a. From these elements a picture may be drawn of the flows of energy and magnetisation in any transmission and distribution system. The ribbons show graphically the equality between inflowing and outflowing energy, and between inflowing and outflowing magnetisation. A single flow of energy may have associated with it two or more separate flows of magnetisation, as shown in fig. 10. Here a synchronous condenser forms a local source of magnetisation for the induction motors at the end of a transmission line, thus saving the losses of transforming and transmitting this flow, as well as performing other useful functions. The generator is shown as furnishing the magnetising power for motors in its vicinity. The electric phenomena previously described are those which result from the storage of energy in an electric circuit due to magnetisation. Energy may, however, also be stored in another form due to electric charging Where the electricity is used in the form of alternating currents, the electric charging current, like the magnetising current, must transport this energy to the part charged and back to the source periodically. Charging power must flow to every part where there is electrostatic capacity. With charging power, as with magnetising power, the current and potential are in quadrature. In fact, charging power is the same as magnetising power, except that the direction of flow is reversed. That is, a kilovolt-ampere of charging power flowing south is the same as a kilovolt-ampere of Synchronous Motor (Over Excited i Alternating Generator SKZflF 180 KW induction Motor 80k.w. Fig. 9.—Power Factors of a Branched Circuit | Leading magnetising power flowing north. The single term, magnetising power, is then sufficient for both. The choice of the term magnetising power, instead of charging power, furnishes the basis of the convention which has been used in indicating the direction of flow of this kind of accelerating power. However, this difference should be noted—an alter- nating-current electric condenser is always a source of magnetising power, while an alternating-current magnet is always a sink in which such power disappears. The electric condenser, therefore, may be used as a substi- tute for the direct-current magnets of an alternator in furnishing the magnetisation of a transmission system. An alternator without direct-current field excitation may receive all needed excitation from an electric condenser, and an induction motor may operate as an induction generator, receiving its magnetisation from a condenser. These results are obtained in practice, though they are not the normal operating conditions on high-tension transmission systems. A rotating machine structurally identical with an alternator or synchronous motor, but not performing any mechanical work, may furnish the magnetising power for a system, in whole or in part, much as an electrostatic condenser would, and hence is called a synchronous condenser. Fig. 11’ shows the essentially different behaviour of an electrostatic condenser and a synchronous condenser as the voltage changes. The flow of magnetising power Transformer TIUN$N1SSIQN UNC Transformer (Step l*) (Step Omm) Induct,on Motor fodvdim, Motor, Fig. io.—Flow of Energy and Magnetisation through Transmission Line. from an electrostatic condenser increases as the square of the voltage. Magnetising power flows from a synchronous condenser only when the circuit voltage is below that corresponding to the excitation of the con- denser. If these voltages are equal the synchronous condenser is neutral as -regards magnetising power. If the circuit voltage is higher, the synchronous condenser absorbs magnetising power, and ceases to be like a con- denser, becoming similar to a reactor. The phenomena due to charging power are not peculiar to electrical transmission. If the steam ports of an engine are permanently closed when the piston is in mid position in the cylinder, it cannot be moved in either direction without compressing the air on one side and expanding that on the other side. If the engine shaft is rotated the piston will require a reciprocating force to overcome the air pressure, and this force will be zero at midstroke and maximum at the dead point; that is, it is in quadrature with the motion. For a given direction of motion the direction of this force will be opposite to that which would be required for acceleration. This reversal of one component, but not of both, reverses the direction of the power. Consequently such an air- cushioned piston becomes a source of accelerating power. As it passes the dead point the flywheel now has its minimum instead of its maximum velocity. The effect of connecting the air cylinder to the wheel at this point is to energise it. Exciter Synchronous Condenser Excitation 100% UneYoitage uo% Excitation 100% Line Voltage 100% Electrostatic Condenser Line Voltage UO% Line Voltage 100% Line Voltage 90% No Flow of Magnetization Excitation too% lune Voltage 90% Fig. 11.—Flow of Magnetisation at Various Line Voltages. Out no wmg Magnetization 8!%KVA Fig. 12 shows that the outflow of accelerating power from ah air cylinder is like the outflow of magnetising power from an electrostatic condenser—one energises the flywheel, the other magnetises the generator. Con- versely, the reciprocating piston and the alternating magnet each take a corresponding inflow and de-energise the flywheel and de-energise the generator respectively. If the two flywheels are combined, the energising and de-energising processes may cancel. The flywheel then becomes unnecessary to maintain the motion and conse- AirCyhnder Fly Wheel Partial Vacuum Compressed Air Fty Wheel Piston Accelerating Power Electrostatic Condenser Generator Generator Alternating Magnet Magnetizing Power Flowing from Qanerpfor Magnetizing Power Flowing from Condenser to Magnet Fig. 12.—Flow of Accelerating Power and Magnetising Power in Oscillating Circuits. quent flow of accelerating power, and the reciprocating motion of the piston may be maintained by connecting it directly to the air cylinder. It is then merely a weight oscillating at the end of an air spring. The two generators may be similarly combined and eliminated, giving an electrical oscillating circuit of a magnet and a condenser. Alleged Breach of Charter Party.—In the King’s Bench Division last week, an appeal was heard against the judgment given by Mr. Justice Pim at the Belfast Summer Assizes, for £920 for the plaintiffs in an action by Messrs. Alexander King Limited, coal merchants, Wellington Quay, against Messrs. Howden Brothers, ship owners, Larne, for breach of charter party to convey coal from Garston to Belfast at the rate of a cargo a month. The “ Kilcoan ’’ was torpedoed by a German submarine in January, when the vessel and cargo were lost. Mr. Justice Gibson and Mr. Justice Kenny, in setting aside the judgment for the plaintiffs and entering judgment for the defendants with costs, held that a provision in the charter party for the conveyance of 25,000 tons of coal for a year in monthly quantities in “ the good steamer ‘ Kilcoan,’ or a substitute at owners’ option,” was inserted for the benefit of the owner of the vessel, and was intended to apply so long as the “ Kilcoan,” or the substitute vessel had not succumbed to the perils named in the charter party. The plaintiff’s contention was that the words of the charter party to convey the cargo in the “ Kilcoan ” or “ substitute at owner’s option,” imposed an obligation on the defendants to provide a continuous service until the whole 25.000 tons were delivered. Defendants argued that such an interpretation would create an unheard of liability. His lordship adopted the defendant’s construction, holding that the language did not justify the plaintiffs’ construction, and that option was introduced to give the owners a certain liberty of action, in their business, the loss of the “ Kilcoan ” probably not being contemplated as a reason for the option.