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HISTORY OF TECHNOLOGY, TECHNOLOGY, OBJECTS AROUND US
Electric generator. History of invention and production
Directory / The history of technology, technology, objects around us An electric generator is a device in which non-electrical forms of energy (mechanical, chemical, thermal) are converted into electrical energy.
For a long time, physicists in different countries tried to discover this dependence, but failed. In fact, if, for example, a permanent magnet lies next to a conductor or coil, no current arises in the conductor. But if we start to move this magnet: move it closer or further away from the coil, insert and remove the magnet from it, then an electric current appears in the conductor, and it can be observed during the entire period during which the magnet moves. That is, an electric current can only occur in an alternating magnetic field. For the first time this important pattern was established in 1831 by the English physicist Michael Faraday. After a series of experiments, Faraday discovered that an electric current arises (is induced) in all those cases when there is a movement of conductors relative to each other or relative to magnets. If you introduce a magnet into the coil or, what is the same, stir the coil relative to a fixed magnet, a current is induced in it. If you move one coil to another, through which an electric current passes, a current also appears in it. The same effect can be achieved when the circuit is closed and opened, since at the moment of switching on and off, the current increases and decreases gradually in the coil and creates an alternating magnetic field around it. Therefore, if there is another, not included in the circuit, close to such a coil, an electric current arises in it.
Faraday's discovery had enormous implications for technology and all of human history, as it now became clear how to convert mechanical energy into electrical energy, and electrical energy back into mechanical energy. The first of these transformations formed the basis for the operation of the electric generator, and the second - for the electric motor. However, the very fact of the discovery did not yet mean that all the technical problems along this path were resolved: it took about forty years to create a workable generator and another twenty years to invent a satisfactory model of an industrial electric motor. But the main thing: the principle of operation of these two most important elements of modern civilization became obvious precisely thanks to the discovery of the phenomenon of electromagnetic induction. The first primitive electric generator was created by Faraday himself. To do this, he placed a copper disk between the N and S poles of a permanent magnet. When the disk rotated in a magnetic field, electric currents were induced in it. If current collectors in the form of sliding contacts were placed on the periphery of the disk and in its central part, then a potential difference appeared between them, as on a galvanic battery. Closing the circuit, it was possible to observe the continuous passage of current on the galvanometer.
The Faraday installation was suitable only for demonstrations, but after it the first magnetoelectric machines appeared (as electric generators that used permanent magnets were called), designed to create working currents. The earliest of these was Pixia's magnetoelectric machine, constructed in 1832.
The principle of its operation was very simple: by means of a crank and a gear, the poles of a horseshoe-shaped magnet AB, lying opposite them, moved past the fixed, equipped with cores coils E and E', as a result of which currents were induced in the coils. The disadvantage of Pixia's machine was that heavy permanent magnets had to be rotated in it. Subsequently, the inventors usually made the coils rotate, leaving the magnets stationary. True, in this case it was necessary to solve another problem: how to divert current from rotating coils into an external circuit? This difficulty, however, was easily overcome. First of all, the coils were connected in series with one end of their wiring. Then the other ends could serve as generator poles. They were connected to the external circuit using sliding contacts.
The sliding contact is arranged as follows: two insulated metal rings b and d were attached to the axis of the machine, each of which was connected to one of the poles of the generator. Two flat metal springs B and B' rotated around the circumference of these rings, on which an external circuit was enclosed. With such a device, there were no longer any difficulties from the rotation of the axis of the machine - the current passed from the axis to the spring at the point of their contact. Another inconvenience was the very nature of the current generator. The direction of the current in the coils depends on whether they are approaching the pole of the magnet or moving away from it. It follows from this that the current arising in a rotating conductor will not be constant, but variable. As the coil approaches one of the poles of the magnet, the current strength will increase from zero to some maximum value, and then, as it moves away, again decrease to zero. With further movement, the current will change its direction to the opposite and will again increase to some maximum value, and then decrease to zero. During subsequent rotations, this process will be repeated. So, unlike an electric battery, an electric generator creates an alternating current, and this has to be taken into account. As you know, most modern electrical appliances are designed in such a way as to be powered by alternating current. But in the XNUMXth century, alternating current was inconvenient for many reasons, primarily psychological, since in previous years people were used to dealing with direct current. However, the alternating current could easily be converted into intermittent, having one direction. To do this, it was enough with the help of a special device - a switch - to change the contacts in such a way that the sliding spring passes from one ring to another at the moment when the current changes its direction. In this case, one contact constantly received current in one direction, and the other in the opposite direction.
Such a device of a spring and contact seems, at first glance, very complicated, but in fact it is very simple. Each ring of the commutator was made of two half-rings, the ends of which partly overlap each other, and the springs were so wide that they could slide along two half-rings placed side by side. The halves of the same ring were placed at some distance from each other, but were interconnected. Thus, the half ring a touching the spring c was connected to the half ring a' on which c' slid; b and b' were connected in the same way, so that in one half-turn the spring c, touching a, passed to b, and the spring c' passed from b' to a'. It was not difficult to install the spring in such a way that it would pass from one ring to another at the moment when the direction of the current in the coil winding changed, and then each spring would always give a current of the same direction. In other words, they were permanent poles; one positive, the other negative, while the poles of the coils gave alternating current. An intermittent direct current generator could well replace a galvanic battery, which was inconvenient in many respects, and therefore aroused great interest among physicists and entrepreneurs of that time. In 1856, the French company "Alliance" even launched the serial production of large dynamos powered by a steam engine. In these generators, the cast-iron frame carried horseshoe-shaped permanent magnets fixed in several rows, evenly spaced along the circumference and radially with respect to the shaft. In the intervals between the rows of magnets, bearing wheels with a large number of coils were installed on the shaft. Also, a collector with 16 metal plates was fixed on the shaft, isolated from each other and from the machine shaft. The current induced in the coils during the rotation of the shaft was removed from the collector using rollers. One such machine required a 6-10 hp steam engine for its drive. The big disadvantage of the Alliance generators was that they used permanent magnets. Since the magnetic effect of steel magnets is relatively small, to obtain strong currents it was necessary to take large magnets and in large numbers. Under the action of vibration, the strength of these magnets quickly weakened. Due to all these reasons, the efficiency of the machine has always remained very low. But even with these shortcomings, Alliance generators gained considerable popularity and dominated the market for ten years, until they were supplanted by more advanced machines. First of all, the German inventor Siemens improved moving coils and their iron cores. (These coils with iron inside were called "anchors" or "reinforcements".) The Siemens "double T" anchor consisted of an iron cylinder in which two longitudinal grooves were cut from opposite sides. An insulated wire was placed in the gutters, which was superimposed along the direction of the axis of the cylinder. Such an anchor rotated between the poles of the magnet, which tightly clasped it.
Compared with the previous ones, the new anchor was a great convenience. First of all, it is obvious that a coil in the form of a cylinder rotating around its axis is mechanically more advantageous than a coil mounted on a shaft and rotating with it. In relation to magnetic actions, the Siemens armature had the advantage that it made it possible to very simply increase the number of active magnets (for this it was enough to lengthen the armature and add several new magnets). A machine with such an armature gave a much more uniform current, since the cylinder was tightly surrounded by the poles of the magnets. But these advantages did not compensate for the main drawback of all magnetoelectric machines - the magnetic field was still created in the generator using permanent magnets. Many inventors in the middle of the XNUMXth century were faced with the question: is it possible to replace uncomfortable metal magnets with electric ones? The problem was that the electromagnets themselves consumed electrical energy and required a separate battery or at least a separate magnetoelectric machine to excite them. At first it seemed that it was impossible to do without them. In 1866, Wilde created a successful model of a generator in which metal magnets were replaced by electromagnets, and their excitation was caused by a magnetoelectric machine with permanent magnets connected to the same steam engine that set the large machine in motion. From here there was only one step to the actual dynamo, which excites the electromagnets with its own current. In the same 1866, Werner Siemens discovered the principle of self-excitation. (Simultaneously with him, some other inventors made the same discovery.) In January 1867, he delivered a report at the Berlin Academy "On the transformation of labor power into electric current without the use of permanent magnets." In general terms, his discovery was as follows. Siemens established that in every electromagnet, after the magnetizing current ceased to act, there always remained small traces of magnetism, which were capable of inducing weak induction currents in a coil equipped with a soft magnetic iron core and rotated between the poles of the magnet. Using these weak currents, it was possible to power the generator without outside help. The first self-excited dynamo was created in 1867 by the Englishman Ledd, but it also provided for a separate coil to excite electromagnets. Ledd's machine consisted of two flat electromagnets, between the ends of which two Siemens armatures rotated. One of the armatures provided current to power the electromagnets, and the other to the external circuit. The weak residual magnetism of the cores of the electromagnets at first excited a very weak current in the armature of the first armature; this current ran around the electromagnets and strengthened the magnetic state already present in them. As a result, the current in the armature increased in turn, and the latter increased the strength of the electromagnets even more. Little by little this mutual strengthening went on until the electromagnets acquired their full strength. Then it was possible to set in motion the second armature and receive current from it for the external circuit.
The next step in the improvement of the dynamo was taken in the direction that they completely eliminated one of the armatures and used the other not only to excite the electromagnets, but also to obtain current in the external circuit. To do this, it was only necessary to conduct the current from the armature into the winding of the electromagnet, calculating everything so that the latter could reach its full strength and direct the same current into the external circuit. But with such a simplification of the design, the Siemens armature turned out to be unsuitable, since with a quick change in polarity, strong parasitic currents were excited in the armature, the iron of the cores quickly heated up, and this could lead to damage to the entire machine at high currents. A different form of anchor was needed, more in line with the new mode of operation. A successful solution to the problem was soon found by the Belgian inventor Zinovy Theophilus Gramm. He lived in France and served in the Alliance campaign as a carpenter. Here he became acquainted with electricity. Reflecting on the improvement of the electric generator, Gramm eventually came up with the idea of replacing the Siemens anchor with another one that has an annular shape. An important difference between the ring armature (as will be shown below) is that it does not remagnetize and has permanent poles (Gram came to his discovery on his own, but it must be said that back in 1860, the Italian inventor Pacinotti in Florence built an electric motor with an annular anchor; however, this discovery was soon forgotten.) So, the starting point of Gram's search was to make an iron ring rotate inside a wire coil, on which magnetic poles are induced and thus obtain a uniform current of a constant direction.
In order to present the device of the Gramme generator, let us first consider the following device. In the magnetic field formed by the N and S poles, eight closed metal rings rotate, which are attached at an equal distance from each other to the axis with the help of spokes. Let's designate the topmost ring No. 1 and we will count in the direction of the clock hand. Consider first the rings 1-5. We see that ring 1 covers the largest number of magnetic field lines, since its plane is perpendicular to them. Ring 2 already covers a smaller number of them, since it is inclined to the direction of the lines, and lines do not pass through ring 3 at all, since its plane coincides with their direction. In ring 4, the number of intersected lines increases, but, as you can easily see, they enter it already from the opposite side, since ring 4 faces the magnet pole with its other side compared to ring 2. The fifth ring covers as many lines as the first, but they enter from the opposite side. If we rotate the axis to which the rings are attached, then each ring will sequentially pass through positions 1-5. In this case, when moving from the 1st position to the 3rd, a current appears in the ring. On the way from position 3 to 5, if the lines of force crossed the ring from the same side, a current would appear in it opposite to that in position 1-3, but since the ring changes its position relative to the pole, that is, it turns to it with the other side, the current in the ring retains the same direction. But when the ring passes from position 5 through 6 and 7 again to 1, a current opposite to the first is induced in it.
Replacing now our imaginary rings with turns of a rotating coil tightly wound around an iron ring, we get a Gramme ring in which the current will be induced in exactly the same way as described above. Suppose that the winding wire has no insulation, but the iron core is covered with an insulating sheath and the current induced in the turns of the conductor cannot pass into it. Then each turn of the spiral will be similar to the ring that we considered above, and the turns in each half of the ring will be series-connected ring conductors. But both halves of the ring are connected opposite to each other. This means that currents from both sides are directed to the upper half of the ring, and there, therefore, a positive pole is obtained. In the same way, at the lower point, whence the currents take their direction, there will be a negative pole. One can, therefore, compare the ring to a battery made up of two parts, which are connected oppositely to each other.
If we now connect the opposite ends of the ring, we get a closed DC circuit. In our imaginary device, this can be easily achieved by strengthening the sliding contacts in the form of a spring so that they touch the top and bottom of the rotating ring and discharge the electric current with them. But in reality, the Gramme generator had a more complex device, since there were several technical difficulties here: on the one hand, in order to remove the current from the ring, the turns of the winding must be exposed, on the other hand, in order to obtain strong currents, the winding must be wound tightly and in multiple layers. How to isolate the lower layers from the upper ones? In practice, the Gramm ring was complemented by a special, rather complex device called a collector, which served to drain currents from the winding. The collector consisted of metal plates attached to the axis of the ring and shaped like sectors of a cylinder. Each plate was carefully isolated from neighboring sectors and from the axis of the ring. The ends of each sector of the winding were connected to one of the metal plates, and sliding springs were placed so that they were constantly in connection with the uppermost and lowermost sectors of the winding. From both halves of the winding, a direct current was obtained, directed to the spring that was connected to the upper sector. The current bypassed the upper circuit and returned to the ring through the lower spring. Thus, the poles moved from the surface of the ring itself to its axis, from where it was much easier to remove the current. In this form, the original model of the electric generator was embodied. However, she was unable to work. As Gramm wrote in his memoirs about his invention, a new difficulty appeared here: the ring on which the conductor was wound was strongly heated due to the fact that currents were also induced here with the rapid rotation of the generator. As a result of overheating, the insulation continually failed.
Puzzling over how to avoid this trouble, Gramm realized that the iron core of the armature cannot be made solid, since in this case the harmful currents turn out to be too large. But by breaking the core into pieces so that gaps were formed in the path of the emerging currents, it was possible to greatly reduce their harmful effect. This could be achieved by making the core not from a single piece, but from wire, imposing it in the form of a ring and carefully isolating one layer from another. A winding was then wound onto this wire ring. Each armature sector was a coil of many turns (layers). Separate coils were connected in such a way that the wire continuously ran around the iron ring and, moreover, in the same direction. From the junctions of each pair of coils there was a conductor to the corresponding collector plate. The greater the number of revolutions of the coil, the greater the current could be removed from the ring.
The armature made in this way was mounted on the axis of the generator. To do this, the iron ring on the inside was supplied with iron spokes, which were fastened to the collector with a massive ring mounted on the axle of the machine. The collector, as already mentioned, consisted of separate metal plates of the same width. The individual collector layers were isolated from each other and from the generator axis.
To remove the current, collector brushes were used, which were elastic brass plates that fit snugly against the collector in the appropriate places. They were connected to the clamps of the machine, from where the direct current flowed into the external circuit. The wire leading to one of the clamps, in addition, formed a winding of electromagnets. The simplest connection of the generator to the electromagnet windings could be obtained by connecting one end of the electromagnet winding to one of the collector brushes, for example, the negative one. The other end of the electromagnet winding was connected to the positive brush. With this connection, the entire generator current passed through the electromagnets. In general, Gramm's first dynamo consisted of two iron vertical posts connected at the top and bottom by rods of two electromagnets. The poles of these electromagnets were located in their middle, so that each of them was, as it were, composed of two, the identical poles of which were facing each other. It is possible to consider this device differently and consider that the two halves adjacent to each rack and connected by it formed two separate electromagnets, which were connected by the same poles above and below. In those places where the pole was formed, special-shaped iron nozzles were attached to the electromagnets, which entered the space between the electromagnets and wrapped around the ring-shaped anchor of the machine. The two posts that connected both electromagnets and formed the basis of the whole machine also served to hold the armature axle and the machine pulleys.
In 1870, having received a patent for his invention, Gramm formed the Society for the Manufacture of Magneto-Electric Machines. Soon mass production of his generators was launched, which made a real revolution in the electric power industry. Possessing all the advantages of self-excited machines, at the same time they were economical, had a high efficiency and provided a practically constant current. Therefore, Gramma machines quickly replaced other electric generators and became widespread in a wide variety of industries. Only then did it become possible to easily and quickly convert mechanical energy into electricity. As already mentioned, Gramm created his generator as a direct current dynamo. But when interest in alternating current sharply increased in the late 70s and early 80s of the XNUMXth century, it did not cost him much work to remake it for the production of alternating current. In fact, for this it was only necessary to replace the collector with two rings along which the springs slide. At first, alternating current generators were used only for lighting, but with the development of electrification, they began to receive more and more use and gradually replaced direct current machines. The original design of the generator has also undergone significant changes. The first Gramm machine was bipolar, but later multi-pole generators were used, in which the armature winding passed four, six or more alternately installed poles of an electromagnet with each revolution. In this case, the current was not excited from both sides of the wheel, as before, but in each part of the wheel facing the pole, and from here it was diverted to an external circuit. There were as many such places (and, accordingly, brushes) as there were magnetic poles. Then all the brushes of the positive poles were connected together, that is, connected in parallel. The same was done with the negative brushes. As the power of the generators increased, a new problem arose - how to remove the current from the rotating armature with the least losses. The fact is that at high currents, the brushes began to spark. In addition to large losses of electricity, this had a detrimental effect on the operation of the generator. Then Gramm considered it rational to return to the earliest design of the electric generator used in Pixia's machine: he made the armature stationary, and made the electromagnets rotate, because it was easier to remove the current from the stationary winding. He placed the armature coils on an iron fixed ring and made the electromagnets rotate inside it. He connected individual coils with each other so that all those coils that were currently subjected to the same action of electromagnets were connected in series. Thus, Gramm divided all the coils into several groups and used each group to deliver current to a separate independent circuit. However, the electromagnets that excite the current had to be supplied with direct current, since the alternating current could not cause an invariable polarity in them. Therefore, with each alternator, it was necessary to have a small DC generator, from where the current was supplied to the electromagnets using sliding contacts. Author: Ryzhov K.V.
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