From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Page from 'The Electrical Review' detailing a D.C. generator for constant pressure at variable speed.
| Identifier | ExFiles\Box 38\1\ Scan029 | |
| Date | 4th October 1918 | |
| X.3405. Vol. 83. No. 2,132, OCTOBER 4, 1918.] THE ELECTRICAL REVIEW. 335 Closest concentration on one subject over longer hours than these must produce staleness and mental fatigue; but the man who is free outside those hours can live farther from his work and get more variety of scenery, live a healthier life, and have a chance of occupation in his home life. At the present moment it also aids in daylight saving and economy of fuel. But the point of permanent value is the better life of the individual and its consequent beneficial reaction on the life of the nation. Such a life would leave the experienced business men with time and energy to devote their attention to local and Imperial Government, instead of leaving it to professional politicians and journalists. But, even apart from these points, the earlier hours are an essential to our national progress and to our healthy national, mental, and physical life. Now, when men are working with women and untrained assistants, their labour is far more intensive and fatiguing. Many a man is keeping his own card indexes, and doing clerical work he would never have touched three years ago—there are still unemployed women who could do it for him. He may do it better than they, but his hours are excessive if he does it all, or else he neglects his proper business. Probably the best hours for a man to work are from 9 until 4.30, with only half an hour for lunch. He would then not have time to eat or drink too much at mid-day, and would be far less sleepy in the afternoon. That, however, is a matter of opinion and of detail. The national interest demands that we should attend to the broad principles of the matter, and carry out at once the reforms that are urgently needed. We are a nation at war, and each must do his best. To do that he must work under the best conditions possible. Moreover, it is a sacred trust to those who are fighting for us that the world to which they return must be better than the old. Reconstruction cannot be relegated to a post-war problem. It must be done by us now, quickly, so that there is an adequate recompense to those who return, for all they have suffered. A D.C. GENERATOR FOR CONSTANT PRESSURE AT VARIABLE SPEED. A paper by S. R.{Sir Henry Royce} Bergman (Journal of the A.I.E.E., Vol. 37, No. 8), what is stated to be a new solution of this problem is presented. The advantages of the machine described are: the machine is self-excited and regulates independently of speed and load; it may be compounded; no external regulating device is used; the regulation is instantaneous and approximately independent of the heating. Fig. 1 illustrates, diagrammatically, the principle of the machine. The armature is series wound, and the field contains twice as many poles as the number of poles for which the armature is wound. In the case illustrated, the armature is wound for two poles and the field contains four poles, symmetrically located. The load is taken from the brushes b and c and a third brush a is placed 90 electrical degrees from the load brushes. The field may be considered to consist of two independent magnetic circuits, one of which circuits ϕ₁, is saturated, and the corresponding flux, ϕ₁, is called the main flux of the machine. The second magnetic circuit ϕ₂ is not saturated, and the corresponding flux ϕ₂ is called the cross flux. The flux ϕ₁ generates, between the brushes b and d, an E.M.F. which is called the main voltage of the machine. The flux ϕ₁ does not generate any E.M.F. between the brushes b and c. Similarly the flux ϕ₂ generates, between the brushes b and c, an E.M.F. which is called the cross voltage. This flux does not generate any E.M.F. between the brushes b and d.{John DeLooze - Company Secretary} The excitation of the machine is taken from the brushes a and b, for which reason the brush a is called the exciting brush. The excitation consists of two multiple branches, one branch exciting the main poles and the second branch exciting the cross poles. The two fluxes ϕ₁ and ϕ₂ are entirely independent of each other, which may be verified by separately exciting the machine, and tests show that if the main excitation is varied only the main voltage is affected, the cross voltage remaining constant; and if the cross excitation is varied only the cross voltage is affected, the main voltage remaining constant. The directions of the main and the cross fluxes are such that the difference between these fluxes is interlinked, with the line brushes b and c, as shown in the figure, and thus the line voltage bc is the difference between the main voltage bd{Mr Berend} and the cross voltage ac. Hence, the voltage ab = bd{Mr Berend} - ac. Since the main circuit is saturated the flux ϕ₁ remains constant and the main voltage bd{Mr Berend} is proportional to the speed. Therefore, the excitation of both the main and the cross fields is proportional to the speed. The cross circuit not being saturated, the cross flux ϕ₂ will increase in proportion to the speed, and, hence, the cross voltage ac must increase with the speed. The cross circuit should not be entirely unsaturated, since then the line voltage would increase too fast and the machine volt. would decrease with increasing speed. The cross flux should approach saturation, and it is possible to choose the saturation of the cross magnetic circuit, so that the line voltage bc remains constant. In fig. 2 is shown the variation of the different voltages with the speed. Since the excitation is taken from the brushes a and b the variation of the exciting ampere-turns follows the main voltage ab and may, therefore, in proper scale, be read from the curve AB. From these curves may be determined the amount of flux in each magnetic circuit for any given excitation, and in fig. 3 are plotted the two fluxes against the excitation. These saturation curves show that over the working range the main magnetic circuit is nearly saturated and the cross magnetic circuit at first is unsaturated, but from a certain point, where the curve bends, this circuit starts to approach saturation. Since the line current is taken from the brushes a and c (fig. 1), there exists an armature reaction or, in the direction of ac. This armature reaction may be resolved in two components, one on in the direction of the main flux, and the other on in the direction of the cross flux. The main magnetic circuit being saturated, the additional excitation, due to the armature reaction, cannot add anything to the main flux. The component on in the direction of the cross flux will, however, interfere with this flux, and would disturb the regulation of the machine. In order to overcome this influence a series winding is added to the cross poles; this winding should have an equal and opposite strength to the armature reaction working in this direction, and is called the compensating winding. The location of this winding is shown in fig. 5. By changing the strength of the compensating winding it is possible to obtain either rising or falling FIG. 1.—CONSTANT PRESSURE GENERATOR. FIG. 2.—VARIATION OF VOLTAGES WITH SPEED. 1.5. KW., 32-VOLT, 1,200/3,200 R.P.M. GENERATOR. FIG. 3.—FLUXES AGAINST EXCITATION. FIG. 4.—GENERATOR AND MOTOR VOLTAGE VARIATION ON TEST. FIG. 5.—COMPLETE DIAGRAM OF CONNECTIONS. | ||