Commutator

“ Commutator.—That part of a dynamo-electric machine to which all of the armature wires are connected and in which the alternating-electromotive force, actually generated in the armature winding, is made to appear as a direct-electromotive force in the external circuit. ”

“ The Dynamo Form.—Consult the diagram, Fig. 47. The iron heads A represent the bar in the [127] previous diagrams, and B the wire around the bar. C is the armature, which in this case represents a number of loops, or coils, and D is the commutator, which is used in the direct current machine to correct the alternations referred to in the previous diagrams, so as to send the current in one direction only, the commutator brushes E being used to carry off the current for use. ”

“ It is known that in machines of great electromotive force—such, for instance, as those used for are lights—whenever one commutator bar or plate comes out of contact with the collecting brush a spark appears on the commutator. ”

“ In the continuous current machine, the commutator and brushes are so arranged as to take up all the impulses of the same polarity and conduct them away by one brush, and gathering all the impulses of the opposite polarity and conducting them away by another brush. ”

“ If the current is not so interrupted, it cannot be felt at all, which may be proved by lifting up the spring on the spindle of the ordinary kind. The current is an alternating one, and changes its direction throughout the circuit, however extended it may be, at every half revolution. The current must be commutated. If it is required to have a continuous current, use must be made of what is termed a commutator, and I shall endeavour to explain the manner in which it acts as simply as possible. ”

“ When an armature is wound with a number of coils the direction of the current is reversed, by the commutator, in each coil as it reaches the point where its usefulness ends, and where, if it continued to flow in the same direction, it would act to hold the armature back. ”

“ In re-turning the commutator, a sharp pointed tool should be used with a very fine feed. A broad nosed tool ought not to be used, as it is liable to burr over the segments. After turning, the commutator should be lightly filed with a dead smooth file, and finally polished with coarse and fine sandpaper. After the commutator has been turned and polished, the insulation between the segments should be lightly scraped with the tang of a small file to remove any particles of metal or burrs which might short circuit the commutator. ”

“ Both ends of the wire are connected with a multiplicator, the one at my end consisting of one hundred and seventy, that in Weber's laboratory of fifty coils of wire, each wound around a one-pound magnet suspended according to a method which I have devised. By a simple contrivance—which I have named a commutator—I can reverse the current instantaneously. Carefully operating my voltaic pile, I can cause so violent a motion of the needle in the laboratory to take place that it strikes a bell, the sound of which is audible in the adjoining room. ”

“ Each sector of fig. 16 will therefore replace two halves of a pair of adjacent split-rings, if the end and beginning of a pair of adjacent coils are connected to it in a regular order of sequence. The four sectors are insulated from one another and from the shaft, and the whole structure is known as the “commutator,”15 its function being not simply to collect the current but also to commute its direction in any coil as it passes the interpolar gap. ”

“ In regular machines there are many loops of wire and several segments to the commutator. The rotating coils are wound upon an iron core, so that the lines of force, in passing from one pole to the other, will meet with as little resistance as possible. The coils, core, and commutator, taken together, are called the armature. The magnets which furnish the field are called the field-magnets. These are electromagnets, the current from the dynamo, or a part of it, being used to excite them. ”

“ In testing with the Queen Acme set how should the plugs be placed in the commutator?
Ans. Always make the arm A the smaller except when the two arms are of equal value.
Ques. If the resistance being measured is higher than 6,100 ohms, or lower than 1,100 ohms, how should the commutator plugs be placed? ”

“ The external appearance of a typical armature with lap-winding is shown in fig. 24.
A sound mechanical construction of the commutator is of vital importance to the good working of the continuous-current dynamo. The narrow, wedge-shaped sectors of hard-drawn copper, with their insulating strips of thin The commutator. mica, are built up into a cylinder, tightly clamped together, and turned in the lathe; at each end a V-shaped groove is turned, and into these are fitted rings of micanite of corresponding section (fig. 19) ”

“ If I propose to find, for instance, with how many series of convolutions I attain the maximum of the current for my magnet and armature, when I take a length of 850 English inches for the wire of the multiplier and the connecting wires together, I have
The formula gives for , and the formula (F.) gives the maximum of increase . We shall obtain therefore the maximum of the current at somewhat about thirteen series of convolutions, and the current then becomes about 115 times stronger than when produced by one convolution. ”

“ The long and constant persuasion that all the forces of nature are mutually dependent, having one common origin, or rather being different manifestations of one fundamental power, has made me often think upon the possibility of establishing by experiment, a connection between gravity and electricity, and so introducing the former into the group, the chain of which (including magnetism, chemical force, and heat,) binds so many and such varied exhibitions of force together by common relations. ”

“ In order to find the resultant force between two bodies we might divide each of them into its elements of volume, and consider the repulsion between the electricity in each of the elements of the first body and the electricity in each of the elements of the second body. We should thus get a system of forces equal in number to the product of the numbers of the elements into which we have divided each body, and we should have to combine the effects of these forces by the rules of Statics. ”

“ Imagine, for instance, a ring everywhere of equal thickness and homogeneous, having, at any one place, in its whole thickness, one and the same electrical tension, i.e. inequality in the electrical state of two surfaces situated close to each other, from which causes, when they have come into action, and the equilibrium is consequently disturbed, the electricity will, in its endeavour to re-establish itself, if its mobility be solely confined to the extent of the ring, flow off on both sides. ”

“ We shall then investigate certain general theorems by which Green, Gauss, and Thomson have indicated the conditions of solution of problems in the distribution of electricity. One result of these theorems is, that if Poisson's equation is satisfied by any function, and if at the surface of every conductor the function has the value of the potential of that conductor, then the function expresses the actual potential of the system at every point. We also deduce a method of finding problems capable of exact solution. ”

“ It thus appears by the combined evidence of the Method of Agreement, the Method of Concomitant Variations, and the most rigorous form of the Method of Difference, that neither of the two kinds of electricity can be excited without an equal [Pg 457] excitement of the other and opposite kind: that both are effects of the same cause; that the possibility of the one is a condition of the possibility of the other, and the quantity of the one an impassable limit to the quantity of the other. ”

“ The experiments which I have tried have continually deepened in me the belief that any change in the state of aggregation of particles—in other words, any change which results in a modification of attracting force—whether gravitative or the commonly called chemical attracting forces, results in an electrical potential; and, conversely, that the passage of electricity through any medium produces a change of aggregation of the molecules and atoms. ”

“ The result of this operation is called the Line-integral of the force. It represents the work done on a body carried along the line. In certain cases in which the line-integral does not depend on the form of the line, but only on the position of its extremities, the line-integral is called the Potential.
In the case of fluxes, we have to take the integral, over a surface, of the flux through every element of the surface. The result of this operation is called the Surface-integral of the flux. It represents the quantity which passes through the surface. ”

“ But as the induction-current close to the wire dies away, a new induction-current is generated in the medium beyond, so that the space occupied by the induction-current is continually becoming wider, while its intensity is continually diminishing. ”

“ Discussions as to transmission by contact are not the fundamental ones, as the above actual material illustration shows: the single comprehensive basis of dynamics into which all such partial modes of explanation and representation must fit and be coordinated is the formula of Stationary Action, including, as the particular case which covers all the domain of steady systems, the law that the mutual forces of such a system are derived from a single analytical function which is its available potential energy. ”

“ But in many other cases we have to consider not merely the laws which regulate the actions of our ultimate causes, but a system of mechanism, or a structure of parts, through the intervention of which their effects become sensible to us. Thus, in the delicate and curious electro-dynamic theory of Ampere, the mutual attraction or repulsion of two magnets is referred to a more universal phenomenon, the mutual action of electric currents, according to a certain fundamental law. ”

“ And when the union is broken by physical force, it is surprising to notice the limited number of points, like pin points, where the cohesion has occurred; whilst the weight of the lump of lead upheld against the force of gravitation reminds one forcibly of the attraction of a mass of soft iron by a powerful magnet, and leads the philosophic inquirer to speculate on the principle of cohesion being only some masked form of magnetic or electrical attraction. ”

“ Since the potential of an electrified point at a distance is the charge of electricity divided by the distance, the ratio of a quantity of electricity to a potential may be represented by a line. Hence all the coefficients of capacity and induction are of the nature of lines, and the coefficients of potential are of the nature of the reciprocals of lines. ”

“ In like manner we may conceive the potential of a material system as a function found by a certain process of integration with respect to the masses of the bodies in the field, or we may suppose these masses themselves to have no other mathematical meaning than the volume-integrals of where is the potential. ”

“ But whether this final unification be accepted or not, it is certain that these monads can not be considered apart from the ether. It is on their interaction with the ether that their qualities depend—and without the ether an electric theory of matter is impossible.
Surely we have here a very extraordinary revolution. Two centuries ago electricity seemed but a scientific toy. It is now thought by many to constitute the reality of which matter is but the sensible expression. ”

“ But as the number of atoms in any stratum is the measure of the force that emitted that stratum, that force itself is directly proportional to the square of its stratum's distance from the center. Now, on the fulfilment of the diffusion, the modus operandi of the attractive force is, of course, the converse of that of the diffusive; in other words, each particle of matter seeks its original condition of unity by attracting its fellow-atoms with a force inversely proportional to the square of the distances between them. ”

“ If we make an axis of compression parallel to a tourmaline plate we obtain displacement of the rings in the four quadrants by a quarter-interval; but the phænomenon is in that case not reciprocal, as a revolution here takes place similar to that which occurs when we look from the opposite side at an electric current in which the circuit is complete, and which is made to proceed in a circular form ; the first and third quadrant then become the second and fourth, and vice versâ. ”

“ It is always possible when one of the functions or is known, to determine the other so that may be equal to unity. For instance, let us take the plane of and draw upon it a series of equidistant lines parallel to to represent the sections of the family by this plane. ”

“ Z − z=p (X − x) + q (Y − y)
passing through it, where X, Y, Z are current co-ordinates, and call this association a surface-element; and if two consecutive elements of which the point (x + dx, y + dy, z + dz) of one lies on the plane of the other, for which, that is, the condition dz = pdx + qdy is satisfied, be said to be connected, and an infinity of connected elements following one another continuously be called a connectivity, then our statement is that a connectivity consists of not more than ∞2 elements, the whole number of elements (x, y, z, p, q) that are possible being called ∞5. ”

“ When we see one body acting on another at a distance, before we assume that the one acts directly on the other we generally inquire whether there is any material connexion between the two bodies, and if we find strings, or rods, or framework of any kind, capable of accounting for the observed action between the bodies, we prefer to explain the action by means of the intermediate connexions, rather than admit the notion of direct action at a distance. ”