In the chapter devoted to the invention of the telegraph, it has commented on the fact that in 1820 it was discovered the interaction between the electric current flowing in the conductor, and the magnetic needle. This phenomenon has been well explained and summarized by the French physicist Ampere, which found that the magnetic properties of a body are due to the fact that the closed electric currents flowing within it. (Or, in modern parlance, any electric current creates a magnetic field around the conductor.) Thus, any magnetic interactions can be seen as a consequence of the electrical. However, if the electric current causes magnetic phenomena, it was natural to assume that the magnetic phenomena may cause an electric current. For a long time physicists in different countries have tried to find this dependence, but failed. In fact, if, for example, next to the conductor or the coil is a permanent magnet, no current in the conductor occurs. But if we begin to move the magnet: zoom in or remove it from the coil magnet introduced and removed therefrom, the electric current in the conductor occurs, and it is possible to observe throughout the 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 law established in 1831, the English physicist Michael Faraday.
In a series of experiments, Faraday discovered that an electric current is generated (induced) in all cases where there is relative movement of the conductors relative to each other or magnets. If you enter a magnet in a coil or, equivalently, to mix the coil relative to the stationary magnet in it current is induced. If you push one coil to another, through which the electric current, it also appears current. The same effect can be achieved by closing and opening the circuit, because at the time of turning on and off current increases and decreases in the coil gradually and creates around it an alternating magnetic field. Therefore, if in the vicinity of such a coil is different, is not included in the circuit, an electric current in it.
Opening Faraday had a huge impact on the art and all of human history, as it has now become clear how to convert mechanical energy into electrical energy and electrical - mechanical back in. The first of these changes was the basis of the electric generator works, and the second - the electric motor. However, the fact that the opening does not mean that all the technical problems solved in this way: It took about forty years to create a workable generator and another twenty years for the invention of a satisfactory model of industrial electric motor. But the main principle of the two most important elements of modern civilization became evident thanks to the discovery of electromagnetic induction.
The first primitive generator Faraday created himself. For this purpose he has placed a copper disc between the poles N and S of the permanent magnet. By rotating the disc in a magnetic field induces electrical currents in it. If the periphery of the disc and its central portion is placed in a moving current collectors contacts between the potential difference appearing, as in galvanic battery. Closing the circuit can be observed on the galvanometer continuous current flow.
Installing Faraday old enough only for demonstrations, but after it appeared the first magneto-electric machines (so became known as power generators, which are used in permanent magnets), designed to create a working currents. The earliest of these was the magnetoelectric machine Peaks, constructed in 1832.
Its principle of operation was very simple: by still equipped with core coils E and E 'moved by a crank and gear behind them against the poles of a horseshoe magnet AB, whereby the induced currents in the coils. The disadvantage Pixie machine was that it had to rotate the heavy permanent magnets. Subsequently, the inventors are usually forced to rotate the coil, leaving the magnets are fixed. However, at the same time I had to deal with another problem: how to take the external circuit current with a spinning reel? This difficulty, however, was easily overcome. First of all, the coil was connected in series between the one ends of wiring. Then, the other ends of the poles could serve as a generator. They are connected to an external circuit by means of sliding contacts.
The sliding contact is arranged as follows: on the axis of the machine fastened two metal rings insulated b and d, each of which was connected to one of the poles of the generator. On the circumference of the rings were rotated two flat metal springs B and B ', which was concluded on the external circuit. With such a device has not been any trouble from the rotation axis of the machine - the current passed from the axis in the spring at the site of contact.
Another inconvenience is the very nature of an electric current. The current direction in the coils depends on whether they are close to the pole of the magnet or removed from it. From this it follows that the current generated in the rotating conductor is not constant but variable. As we approach the coil to one of the poles of the magnet current intensity will increase from zero to some maximum value, and then - as the distance down to zero again. Upon further movement of the current change its direction for the opposite and will again grow to a certain maximum value, and then decrease to zero. During these rotations, this process will be repeated. Thus, unlike the electric battery, an electric generator produces alternating current and this has to be considered.
As is known, most modern electrical appliances are created so as to be powered by AC power. But in the XIX century AC was uncomfortable for many reasons, primarily psychological, as in previous years are used to dealing with a constant current. However, an alternating current can be easily converted into an intermittent having the same direction. To it was enough with a special device - Switch - change contacts so that the moving coil moves from one ring to another at the time when the current changes direction. In this case one contact receiving current continuously in one direction and the other - opposite.
This spring device and the contact appears, at first glance, a very difficult, but in reality it is very simple. Each switch ring made of two half-rings, the ends of which come partly for each other, and the springs were so broad that they could slide on the two half-rings placed side by side. Half of the same ring placed at a distance from each other, but were interconnected. So, half a, c touches the spring, has been linked with a semicircle of a ', through which glided cprime ;, similarly connected to each other b and b', so that when one half-turn spring c, regarding a, b passed on, and spring c 'passed from b' to a '. It was easy to set the spring so that it is passed from one ring to another at the moment when the current direction is changed, and then each spring at all times gave a current of the same direction in the coil winding. In other words, they were only a permanent pole; one - positive, the other - negative, while the coil pole gave alternating current.
Generator intermittent DC could easily replace inconvenient in many respects, a galvanic battery, and therefore aroused great interest among the then physicists and entrepreneurs. In 1856, the French company "Alliance" even establish serial production of large dynamo, driven by a steam engine. In these generators iron bed is fixedly carried on themselves Fortified several rows of permanent horseshoe magnets arranged uniformly around the circumference and radially relative to the shaft. In between the rows of magnets on the shaft carrying the wheels were made with a large number of coils. Also, the shaft has been reinforced by the collector with 16 metal plates, isolated from each other and from the machine shaft. The current induced in the coil by rotation of the shaft, shot from the collector by means of rollers. One such machine is required for its drive steam engine power 6-10 hp "Alliance" generators big drawback was that they used permanent magnets. Since the magnetic action of steel magnets is relatively small, in order to obtain high currents needed to borrow large magnets and in large numbers. Under the influence of vibration strength of these magnets weakened quickly. Because of all these reasons, the efficiency of the car has always been very low. But even with these drawbacks generators "Alliance" received considerable spread and dominated the market for ten years, until they were replaced by the more sophisticated machines.
First of all, the German inventor Siemens perfected the moving coils and iron cores. (These coils inside the iron are called "anchor" or "reinforcement".) Anchor Siemens in the form of a "double T" consisted of an iron cylinder, which had been cut with two opposite sides of the longitudinal chutes. The troughs placed insulated wire that overlap in the direction of the cylinder axis. Such anchor rotated between the poles of a magnet, which is closely encircled it.
Compared with the same new anchor is of great convenience. First of all, it is obvious that the coil is a cylinder rotating around its axis in the mechanically advantageous coils impaled on the shaft and rotates therewith. With respect to the magnetic effect of the armature Siemens had the advantage that made it possible very simply to increase the number of operating magnets (it was enough to lengthen the anchor and add a few new magnets). The car with such anchor gave a much more uniform current, because the cylinder was tightly surrounded by the poles of magnets.
However, these advantages are not compensated for the major drawback of magnetoelectric machines - the magnetic field is still created in the generator by means of permanent magnets. Before many inventors in the middle of the XIX century, the question arose: whether to replace the uncomfortable metal electric magnets can not? The problem was that the electromagnets themselves consumed electric energy for excitation and required a separate battery, or at least separate magnetoelectric machine. At first it seemed that it is impossible to do without them. In 1866, Wilde created a successful model of the generator, in which metal magnets were replaced by electromagnets and their excitement caused magnetoelectric machine with permanent magnets, bonded to the same steam engine, which is driven by a big car. It was only one step to the actual dynamo that drives the electromagnets his own shock.
Also in 1866, Werner Siemens discovered the principle of self-excitation. (At the same time it made the same discovery some other inventors.) In January 1867, he spoke at the Berlin Academy of the report "On the transformation of the labor force into electric current without the use of permanent magnets." In general, its opening was as follows. Siemens found that each electromagnet after the magnetizing current is stopped to operate, always remain small traces of magnetism, which were able to cause a weak induction currents in the coil provided with a core of soft magnetic iron and rotates between the poles of the magnet. Using these weak currents, could result in a generator without outside help.
The first dynamo, works on the principle of self-excitation, was established in 1867 by Englishman Leddy, but it is still having a separate coil for the excitation of the electromagnets. Ledd machine consisted of two flat magnets, between the ends of which revolved two anchors Siemens. One of the anchors given the current supply to the electromagnets, and the other - to the external circuit. Weak residual magnetism of the cores of the electromagnets initially aroused a very weak current in the armature of the first armature; This current swept electromagnets and strengthened already existing in their magnetic state. Because of this amplified, in turn, the current in the armature, and the latter further increases the power of electromagnets. Little by little, a mutual reinforcement of going up as long as the electromagnets are not acquired its full force. Then it was possible to set in motion the second valve and gain from the current to the external circuit.
The next step in the improvement of the dynamo has been made in that direction, that completely eliminated one of the valves, and used the other is not only to excite the electromagnets, but also for the current in the external circuit. To do this, it was only necessary to conduct current from the armature coil in the electromagnet, calculating everything so that the latter could attain its full strength and to send the same current in the external circuit. But with such a simplification of the structure anchored Siemens turned out to be unsuitable, since the rapid change of polarity in the anchor excited strong parasitic currents, the iron cores quickly warms up, and it could at high currents cause damage to the entire machine. Needed was another form of anchor, more in line with the new mode of operation.
A successful solution to the problem was soon found by the Belgian inventor Zinovy Theophile grams. He lived in France and served in the campaign "Alliance" master carpenter. There he became acquainted with electricity. Reflecting on the improvement of the power generator, Gram eventually came to the idea to replace the anchor Siemens other having an annular shape. An important difference between the anchor ring (as shown below) is that it does not have permanent magnetization reversal and pole (Gram came to his own discovery, but it must be said that even in 1860, Italian inventor Pachinotti Florence built an electric motor with an annular anchor; however, this discovery was soon forgotten).
So, the starting point of searches Gram was to make to rotate inside a wire coil iron ring on which the imposed magnetic poles and thus obtain a uniform current is constant direction.
To submit a Gram generator device, we first consider the following device. In a magnetic field formed by N poles and S, rotate eight closed metal rings, which are attached at an equal distance from each other to the axis by spokes. Let the uppermost ring number 1 and will be considered in the direction of clockwise. Consider the first 1-5 rings. We see that the Ring 1 covers the largest number of magnetic field lines, as its plane is perpendicular to them. The ring 2 already covers a smaller number, since it is inclined to the direction of the lines, and does not pass through the ring line 3, since it coincides with their plane direction. In the ring 4 increases the number of lines crossed, but it is easy to notice, they come in it is already on the other side, as the ring 4 facing the magnet pole his other side, compared with the ring 2. The fifth ring includes the same number of lines as the first but they are included on the opposite side. If we rotate the axis to which are attached the ring, each ring will successively pass through the position 1-5. Thus, when switching from the 1st position to the third ring is a current. On the way from position 3 to 5, if the lines of force crossing the ring with the same hand, the current would appear therein opposite to that in the 1-3 position, but since in this case the ring changes its position relative to the pole that is turned to it by the other party, the current in the ring retains the same direction. But when the ring passes from position 5 and 6 through 7 again to 1, a current is induced therein, opposite the first.
Replacing now our imaginary ring turns rotating coil tightly wound around the iron ring, we get a ring Gram in which current is induced in the same way as described above. Assume that the coil wire is not insulated, but the iron core is covered with an insulating sheath and the current induced in the turns of the conductor can not pass into it. Then, each turn of the spiral is similar to the ring that we discussed above, and the coils in each half of the ring will be a series connected annular conductors. However, both halves of the rings are connected to each other oppositely. So currents from both sides are directed to the upper half of the ring, and there is therefore obtained a positive pole. Similarly, at the lowest point, where the currents have their direction, will be the negative pole. It is possible, therefore, compared with the battery ring consisting of two parts which are oppositely interconnected.
If we now connect the opposite ends of the ring, we get a closed DC circuit. In our imaginary device that 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 shot with them an electric current. But in fact Gram generator had a more complex device, since there was available a few technical difficulties: on the one hand, to remove the current from the ring windings should be exposed, on the other - a winding for high currents to be wound densely and several layers. How, then, to isolate the lower layers from the top?
In practice, the ring Gram complement a special, rather complicated device called a collector, which also served to drain currents of the windings. The collector composed of metal plates attached to the ring axis and having the shape of a cylinder sector. Each plate is carefully isolated from neighboring sectors and from the ring axis. Winding ends of each sector are connected with one of the metal plates, and sliding spring placed so that constantly in conjunction with the uppermost and lowermost winding sectors. Of the two winding halves obtained constant current directed to the spring which has been connected to the upper sector. Current rounds upper circuit and returning to the ring through the bottom of the spring. Thus, the pole surface of the ring moved on its axis, where the current was much easier to remove.
In this form, it embodied the original model of the electric generator. However, it turned out to be unworkable. As Gramm wrote in his memoirs about his invention, there was a new complication: the ring on which was wound conductor, strongly heated due to the fact that here, too, with the rapid rotation of the generator of induced currents. As a result, heat insulation and then it broke down. Breaking my head over how to avoid this trouble, Gram realized that the iron core of the armature can not make a solid, as in this case, harmful currents are too high. However, breaking the core into pieces so as to form gaps arising in the path of currents can be drastically reduce their harmful effects. This can be achieved by preparing the core is not of one piece, and a wire, placing it in a ring and carefully isolating one layer from another. On the wire ring is then wound coil. Each sector represented armature coil of many turns (layers). Individual coils are connected so that the wire runs around continuously iron ring and, moreover, in the same direction. From the connection points of each pair of coils was the conductor to the corresponding plate collector. The greater the number of coil turns, the greater the force current can be removed from the ring.
Thus produced the anchor installed on the generator shaft. To do this, an iron ring on the inner side was supplied with iron spokes, which were fastened to the collector of a massive ring, impaled on the axis of the machine. The collector, as already mentioned, consisted of individual metallic plates of the same width. Separate collector layers being insulated from each other and from the axis of the generator.
To remove the current collector were brushes, is a resilient brass plate tight to the collector in the right places. They were connected with the clamps of the machine, where a constant current is supplied to the external circuit. Wire to one of the terminals, in addition, forms a winding electromagnets. The simplest generator connection to the windings of the electromagnet can be obtained by connecting one end of the solenoid coil with one of the collector brushes, such as negative. The other end of the electromagnet coil connected to the positive brush. With this connection all alternator current passed through the electromagnets.
In general, the first dynamo Gramm was a two iron uprights connected at the top and bottom bars of the two electromagnets. Poles of electromagnets are in their middle so that each of them as it was composed of two like poles which face each other. You can think of this device is different and assume that the two halves adjacent to each rack and connected to it, formed two separate electromagnet that like poles connected at the top and bottom. In those places where the pole was formed, attached to the electromagnets are a special form of iron attachments that were in the space between the electromagnets and bowed annular anchoring the machine. Two racks, connecting both of the electromagnet is the basis of the whole machine, also served to keep the armature shaft and pulley machines.
In 1870, received a patent for his invention, Gramm formed the "Company manufacturing magnetoelectric machine". Soon the mass production of its generators were established which produced a genuine revolution in the power sector. With all the advantages of self-excited machines, they were at the same time economical, have high efficiency and provide virtually unchanged largest current. Therefore Gram machine quickly replaced other power generators, and are widely used in various industries. Then only the opportunity to quickly and easily convert the mechanical energy into electricity.
As already mentioned, Gramm created his generator as a dynamo DC. But when, in the late 70's - early 80-ies of the XIX century, has sharply increased interest in AC, it is not much trouble to alter its AC output. In fact, for this purpose it was necessary to replace only two collector rings which slide spring. First alternators used only for lighting, but with the development of electrification, they began to receive more and more applications, and gradually replaced the DC machine. Initial generator design has also undergone significant changes. The first machine has bipolar Gramm, but subsequently began to apply multipolar generators in which the armature winding is held at each turn by four, six or more of the electromagnet poles are alternately established. In this case, no current is excited on both sides of the wheel, as before, but in each of the wheel facing towards the pole, and here was allocated to an external circuit. Such places (and thus the brushes) was as much as the magnetic poles. Then all the positive pole brushes were connected together, that is connected in parallel. Similarly, we received and negative brushes.
As the generators power a new problem - how to remove the current from the rotating armature with minimal losses. The fact that at high currents the brush sparking started. In addition to large power losses, it has a detrimental effect on the operation of the generator. Then Gram rational thought return to the very early design electric applied in the car pix: he made a fitting fixed and rotating electromagnets made, because to stay in current with a fixed winding it easier. He placed the armature coil on an iron ring fixed electromagnets and made to rotate inside it. Individual coils he linked together so that all of the coils, which are currently subjected to the action identical electromagnets are connected in series. Thus Gramm broke all coils into several groups and each group has used for delivering current to a separate independent circuit. However, the exciting current of the electromagnets it was necessary to feed the direct current as an alternating current could cause them constant polarity. Therefore, each time the alternator was necessary to have a small DC generator, where the current is applied to the electromagnets by means of sliding contacts.