Alternator what. How does an alternator work?

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Induction generator alternating current. In induction alternators, mechanical energy is converted into electrical energy. An induction generator consists of two parts: a movable one, which is called a rotor, and a stationary one, which is called a stator. The operation of the generator is based on the phenomenon of electromagnetic induction. Induction generators have a relatively simple design and allow you to obtain high currents at a sufficiently high voltage. There are many types of induction generators available today, but they all consist of the same basic parts. This is, firstly, an electromagnet or permanent magnet that creates a magnetic field, and, secondly, a winding consisting of series-connected turns in which a variable is induced electromotive force. Since the electromotive forces induced in series-connected turns add up, the amplitude of the electromotive force of induction in the winding is proportional to the number of turns in it.

Rice. 6.9

The number of lines of force piercing each turn varies continuously from maximum value, when it is located across the field, to zero when the field lines slide along the turn. As a result, when the coil rotates between the poles of the magnet, every half turn the direction of the current changes to the opposite, and an alternating current appears in the coil. Current is diverted into the external circuit using sliding contacts. For this purpose, slip rings are attached to the winding axis and attached to the ends of the winding. Fixed plates - brushes - are pressed against the rings and connect the winding with the external circuit (Fig. 6.9).

Let a coil of wire rotate in a uniform magnetic field with a constant angular velocity. The magnetic flux penetrating the coil changes according to the law, here S– coil area. According to Faraday's law, an electromotive force of induction is induced in the winding, which is defined as follows:

Where N– number of turns in the winding. Thus, the electromotive force of induction in the winding changes according to a sinusoidal law and is proportional to the number of turns in the winding and the rotation frequency.

In an experiment with a rotating winding, the stator is a magnet and contacts between which the winding is placed. In large industrial generators, an electromagnet, which is the rotor, rotates, while the windings, in which the electromotive force is induced, are placed in the slots of the stator and remain stationary. In thermal power plants, steam turbines are used to rotate the rotor. The turbines, in turn, are driven by jets of water vapor produced in huge steam boilers by burning coal or gas (thermal power plants) or by decaying matter (nuclear power plants). Hydroelectric power plants use water turbines to turn the rotor, which are rotated by water falling from a great height.

Electric generators play a vital role in the development of our technological civilization, since they allow us to receive energy in one place and use it in another. A steam engine, for example, can convert coal combustion energy into useful work, but this energy can only be used where a coal firebox and a steam boiler are installed. A power plant can be located very far from electricity consumers - and, nevertheless, supply factories, houses, etc. with it.

It is said (most likely, this is just a beautiful fairy tale) that Faraday showed a prototype of an electric generator to John Peel, the British Chancellor of the Exchequer, and he asked the scientist: “Okay, Mr. Faraday, all this is very interesting, but what is the use of it all?”

“What's the point? – Faraday was allegedly surprised. “Do you know, sir, how much taxes this thing will bring to the treasury over time?!”

Transformer.

Transformer. The electromotive force of powerful generators of power plants is great, meanwhile practical use Electricity usually requires not very high voltages, but energy transmission, on the contrary, requires very high voltages.

To reduce losses due to heating of wires, it is necessary to reduce the current in the transmission line, and, therefore, to maintain power, increase the voltage. The voltage produced by the generators (usually around 20 kV) is increased to 75 kV, 500 kV and even 1.15 MV, depending on the length of the transmission line. By increasing the voltage from 20 to 500 kV, that is, by 25 times, line losses are reduced by 625 times.

The conversion of alternating current of a certain frequency, at which the voltage increases or decreases several times with virtually no loss of power, is carried out by an electromagnetic device that has no moving parts - an electrical transformer. A transformer is an important element of many electrical devices and mechanisms. Charging device and toys railways, radios and televisions - transformers work everywhere, lowering or increasing the voltage. Among them there are both very tiny ones, no larger than a pea, and real colossi weighing hundreds of tons or more.

Rice. 6.10

The transformer consists of a magnetic core, which is a set of plates that are usually made of ferromagnetic material (Fig. 6.10). There are two windings on the magnetic circuit - primary and secondary. The one of the windings that is connected to an alternating voltage source is called primary, and the one to which the “load” is connected, that is, devices that consume electricity, is called secondary. Ferromagnetic increases the number of lines of force magnetic field approximately 10,000 times and localizes the flux of magnetic induction within itself, so that the transformer windings can be spatially separated and yet remain inductively coupled.

The operation of a transformer is based on the phenomena of mutual induction and self-induction. The induction between the primary and secondary winding is reciprocal, that is, the current flowing in the secondary winding induces an electromotive force in the primary, just as the primary winding induces an electromotive force in the secondary. Moreover, since the turns of the primary winding cover their own lines of force, an electromotive force of self-induction arises in them. The electromotive force of self-induction is also observed in the secondary winding.

Let the primary winding be connected to an alternating current source with an electromotive force, so an alternating current arises in it, creating an alternating magnetic flux in the transformer magnetic circuit ? , which is concentrated inside the magnetic core and penetrates all turns of the primary and secondary windings.

In the absence of an external load, the power released in the transformer is close to zero, that is, the current strength is close to zero. Let us apply Ohm's law to the primary circuit: the sum of the electromotive force of induction and voltage in the circuit is equal to the product of the current and the resistance. Assuming , we can write: therefore, , Where F– the flux permeating each turn of the primary coil. In an ideal transformer, all the lines of force pass through all the turns of both windings, and since the changing magnetic field produces the same electromotive force in each turn, the total electromotive force induced in the winding is proportional to the total number of its turns. Hence, .

The voltage transformation ratio is equal to the ratio of the voltage in the secondary circuit to the voltage in the primary circuit. For the amplitude values of voltages on the windings, we can write:

Thus, the transformation ratio is defined as the ratio of the number of turns of the secondary winding to the number of turns of the primary winding. If the coefficient is , the transformer will be a step-up transformer, and if it is a step-down transformer.

The relations written above, strictly speaking, are applicable only to an ideal transformer in which there is no magnetic flux dissipation and no energy loss due to Joule heat. These losses may be due to the presence active resistance the windings themselves and the occurrence of induction currents (Foucault currents) in the core.

Toki Fuko.

Toki Fuko. Induction currents can also arise in solid massive conductors. In this case, a closed circuit of induction current is formed in the thickness of the conductor itself when it moves in a magnetic field or under the influence of an alternating magnetic field. These currents are named after the French physicist J.B.L. Foucault, who in 1855 discovered the heating of ferromagnetic cores of electrical machines and other metallic bodies in an alternating magnetic field and explained this effect by the excitation of induced currents. These currents are now called eddy currents or Foucault currents.

If the iron core is in an alternating magnetic field, then internal eddy currents are induced in it under the influence of an induction electric field - Foucault currents, leading to its heating. Since the electromotive force of induction is always proportional to the oscillation frequency of the magnetic field, and the resistance of massive conductors is small, at high frequencies a large amount of heat will be released in the conductors, according to the Joule-Lenz law.

In many cases, Foucault currents are undesirable, so special measures must be taken to reduce them. In particular, these currents cause heating of the ferromagnetic cores of transformers and metal parts of electrical machines. To reduce losses electrical energy Due to the occurrence of eddy currents, transformer cores are made not from a solid piece of ferromagnet, but from separate metal plates isolated from each other by a dielectric layer.

Rice. 6.11

Eddy currents are widely used for melting metals in so-called induction furnaces (Fig. 6.11), for heating and melting metal workpieces, and producing especially pure alloys and metal compounds. To do this, the metal workpiece is placed in an induction furnace (a solenoid through which alternating current is passed). Then, according to the law of electromagnetic induction, induction currents arise inside the metal, which heat the metal and can melt it. By creating a vacuum in the furnace and using levitation heating (in this case, the forces electromagnetic field not only heat the metal, but also keep it suspended out of contact with the surface of the chamber), especially pure metals and alloys are obtained.

Alternating current of industrial frequency is generated at power plants by electric machine synchronous generators specially designed for this purpose. The operating principle of these units is based on the phenomenon of electromagnetic induction. The mechanical energy produced by a steam or hydraulic turbine is converted into alternating current electricity.

The rotating part of the drive or rotor is an electric magnet, which transmits the generated magnetic field to the stator. This is the outer part of the device, consisting of three coils of wires.

Voltage is transmitted through commutator brushes and rings. The copper rotor rings rotate simultaneously with the crankshaft and rotor, causing the brushes to be pressed against them. Those, in turn, remain in place, allowing electric current to be transmitted from the stationary elements of the generator to its rotating part.

The magnetic field produced in this way, rotating across the stator, produces electric currents that charge the battery.

Popular models of welding generators alternating current:

Generator alternating current

There are now many different types of induction generators. But they all consist of the same basic parts. This is, firstly, an electromagnet or permanent magnet that creates a magnetic field, and, secondly, a winding in which a variable is induced EMF- electric driving force (in the considered generator model this is a rotating frame). Since the EMF induced in series-connected turns add up, the amplitude of the induced EMF in the frame is proportional to the number of turns in it. It is also proportional to the amplitude of the alternating magnetic flux (Фm = BS) through each turn.

Operating principle of the generator alternating current next. To obtain a large magnetic flux, generators use a special magnetic system consisting of two cores made of electrical steel. The windings that create the magnetic field are placed in the slots of one of the cores, and the windings in which the EMF is induced are in the slots of the other. One of the cores (usually internal) together with its winding rotates around a horizontal or vertical axis. That's why it's called a rotor. The stationary core with its winding is called a stator. The gap between the stator and rotor cores is made as small as possible to increase the flux of magnetic induction.

In the generator model shown in the figure, a wire frame rotates, which is a rotor (though without an iron core). The magnetic field is created by a stationary permanent magnet. Of course, one could do the opposite: rotate the magnet and leave the frame motionless.

In large industrial generators, it is the electromagnet, which is the rotor, that rotates, while the windings in which the EMF is induced are placed in the stator slots and remain stationary. The fact is that current must be supplied to the rotor or removed from the rotor winding to an external circuit using sliding contacts. To do this, the rotor is equipped with slip rings attached to the ends of its winding.

Fig.1. Structural scheme alternator current

Fixed plates - brushes - are pressed against the rings and connect the rotor winding with the external circuit. The current strength in the windings of the electromagnet that creates the magnetic field is significantly less than the current supplied by the generator to the external circuit. Therefore, it is more convenient to remove the generated current from the stationary windings, and through the sliding contacts to supply a relatively weak current to the rotating electromagnet. This current is generated by a separate generator direct current(exciter) located on the left of the shaft (Currently, direct current is most often supplied to the rotor winding from the stator winding of the same generator through a rectifier).

In low-power generators, the magnetic field is created by a rotating permanent magnet. In this case, rings and brushes are not needed at all.

The appearance of EMF in stationary stator windings is explained by the appearance of a vortex electric field in them, generated by a change in the magnetic flux when the rotor rotates.

A modern electric current generator is an impressive structure made of copper wires, insulating materials and steel structures. With dimensions of several meters, the most important parts of the generators are manufactured with millimeter precision. Nowhere in nature is there such a combination of moving parts that can generate electrical energy so continuously and economically.

ALTERNATING CURRENT

The generator shaft is driven into rotation from a pulley mounted on the engine crankshaft by a V-belt. The V-belt transmission ratio is 1.7-2.0. When a car is moving, the crankshaft rotation speed at idle for modern engines is 500-600 rpm, the maximum speed is 4000-5000 rpm. Thus, the factor of change in the engine speed, and, consequently, the generator shaft, can reach 8 - 10. The generator voltage depends on the speed of its shaft rotation. The higher the frequency, the higher the generator voltage. However, all electrical equipment of the car, especially lamps and instrumentation

devices designed to be powered by DC voltage 12 or 24 V. Maintaining a constant generator voltage, regardless of changes in the rotation speed and load of the generator (switching on consumers), is carried out by a special device called a voltage regulator.

When the engine speed decreases below 500-700 rpm, the generator voltage becomes less than the battery voltage. If the battery is not disconnected from the generator, it will begin to discharge to the generator, which can lead to overheating of the insulation of the generator windings and discharge of the battery. When the engine speed increases, it is necessary to reconnect the generator to the electrical system. The inclusion of the generator in the electrical system when its voltage is higher than the battery voltage, and the disconnection of the generator from the network when its voltage is lower than the battery voltage, is performed by a special device called a relay reverse current.

The generator is designed to deliver a certain maximum current value for a given generator, however, if there is a malfunction in the electrical equipment system (discharged battery, short circuit, etc.), the generator can deliver a current greater than that for which it is designed. Prolonged operation of the generator in this mode will lead to overheating and burning of the winding insulation. To protect the generator from overload, a special device called a current limiter is used.

All three devices - a voltage regulator, a reverse current relay and a current limiter - are combined in one device called a relay regulator.

In some generators, for example G-250, an alternating current reverse current relay and a current limiter may be absent, but the generator design contains devices that perform the functions of these devices.

In Fig. Figure 1 shows the device of the G-250 alternating current generator. The generator has a stator 6 with a three-phase winding made in the form of separate coils mounted on the stator teeth. Each phase has six coils connected in series. The phase windings of the stator are connected by a star, and their output terminals are connected to the rectifier unit 10.

Device alternator current G-250

The stator housing is made of individual electrical steel plates. The excitation winding 4 of the generator is made in the form of a coil and is placed on a steel bushing of the beak-shaped poles of the rotor 13. The bushing, beak-shaped poles of the rotor and slip rings 5 are rigidly fixed to the rotor shaft 3 (press fit on knurling). The magnetic field created by the excitation winding, passing through the ends of the beak-shaped poles, forms the north and south poles on the rotor (Fig. 2) (E.V. Mikhailovsky, “Car Design”, p. 163).

When the rotor rotates, the magnetic field of the rotor poles crosses the turns of the stator winding coils, inducing a variable emf in each phase.

Rectification circuit alternating current

The current in the excitation winding is supplied through brushes 8 (Fig. 1) and contact rings 5, to which the ends of the excitation winding are soldered. The brushes are fixed in the brush holder 9.

The generator stator is secured with tightening bolts between covers 1 and 7, which have brackets for attaching the generator to the engine. In cover 1 on the drive side at the top there is a threaded hole for attaching a tension bar, with which the tension of the generator drive belt is adjusted. The covers are cast from aluminum alloy.

In order to reduce wear, the seat for the ball bearing in the rear cover 7 and the holes in the cover brackets are reinforced with steel bushings.

The covers are equipped with ball bearings 2 and 12 with double-sided seals and lubricant for the entire service life of the bearing.

An external fan 14 (Fig. 1) and a pulley 15 are attached to the protruding end of the rotor shaft 3. The covers have ventilation windows through which cooling air passes. The direction of movement of cooling air is from the cover on the side of the slip rings to the fan.

A rectifier unit 10, assembled from silicon valves (diodes) allowing an operating temperature of the housing plus 150°C, is installed in the cover on the side of the contact rings.

Types of rectifier units

Rectifier unit VBG-1. (Fig. 4) consists of three monoblocks connected into a full-wave three-phase rectifier circuit

Each two rectifier valves are placed in a monoblock, which simultaneously serves as a radiator and a conductive core of the middle point of circuit 3. In the body of the monoblock radiator 4 there are two sockets in which p-n-junctions of the rectifier valves are assembled. In one socket, the pn junction has a p-zone on the body, and in the other, a n-zone. The opposite transition zones have flexible leads 9, which connect the monoblock to the connecting buses 2. The negative bus of the rectifier unit is connected to the generator housing. In later designs of rectifier blocks BPV-4-45 (Fig. 4, b) for a current of 45 A, silicon valves of the VA-20 type are used, which are pressed into heat sinks 12 of negative and positive polarity, three valves each. The heat sinks are isolated from one another by plastic insulator bushings 13. The reverse current of the valves does not exceed 3 mA, and assembled block-10 mA. For generators with a maximum power of up to 1200 Vt (G-228), silicon rectifier blocks VBG-7-G for a current of 80 A (Fig. 4, c) or BPV-7-100 are used. The BPV-7T and BPV-7-100 blocks use VA-20 valves, two in parallel in each arm, six valves in each heat sink. The BPV-7-100 block for a current of 100 A and its electrical circuit are shown in Fig. 4, g.

To reduce the level of radio interference in the blocks, VBR-7-G and BPV-7-100, a capacitor with a capacity of 4.7 μF is installed parallel to the “+” and “-” terminals of the generator. The general view of the BA -20 valve is shown in Fig. 5. The rated current of the valve is 20 A. To simplify the circuit, electrical connections The valves are available in two versions - with direct and reverse polarity to the housings (Fig. 5, b). In valves of direct polarity there will be “+” of the rectified current on the body, in valves of reverse polarity there will be “-” of the rectified current.

Direct and reverse polarity valves differ in the color of the markings applied to the bottom of the housing. Valves with direct polarity: (“+” on the body) are marked with red paint, and valves with reverse polarity (“-” on the body) are marked with black paint.

Silicon valve VA-20

The electrical circuit for connecting the generator windings and rectifiers is shown in Fig. 3, a. When the generator rotor rotates, in each phase it is induced AC voltage the change of which over one period is shown in Fig. 3, b. After straightening, the phase voltage curves will take the form shown in Fig. 3, c. The rectified voltage will be almost constant (line 1 in Fig. 3, c), and the ripple frequency of the rectified voltage will be six times greater than the frequency in the phase windings (Yu.I. Borovskikh, “Design of automobiles,” p. 183).

With increasing rotation speed, the frequency of the current induced in the phase windings of the generator increases alternating current, and the inductive resistance of the windings increases. Therefore, at a high frequency of rotor rotation, when the generator can deliver maximum power, there is no danger of overloading it, since the generator current is limited by the increased inductive reactance of its windings. This is a phenomenon in generators alternating current is called the self-restraint property. Automotive generators G-250, G-270, G-221 and others are designed in such a way that they do not require a current limiter.

The property of the valves to pass current only in one direction (from the generator to the battery) eliminates the need to install a reverse current relay in the relay regulator. Thus, a relay-regulator working with a car generator alternating current, only a voltage regulator can be used. This significantly simplifies the design and reduces the size, weight and cost of the relay regulator. The current paths through the rectifier valves as the windings of the first phase pass through the north and south poles of the rotor are shown in Fig. 3, and arrows. As can be seen from the diagram, if there is a current in the windings of the first phase that is alternating in direction, the current in the load circuit (Rн) will be constant. The process occurs similarly in other phases.

II. THAT. GENERATOR

Failures and malfunctions of the generator are: open or short circuit in the stator winding of the generator or in the excitation winding, broken contact of brushes with rings and sparking of brushes, wear of generator bearings, breakage or weakening of the brush holder spring, breakdown of diodes in the rectifier, weakening of tension (excessive tension) of the drive belt

Generator malfunctions are detected by the readings of an ammeter or warning lamp. If the generator is faulty, the ammeter will show a discharge, and the warning light will light up when the engine is running. Loss of contact between the brushes and the rings occurs from contamination, burning or wear, chipping or wear of the brushes, as well as weakening or breakage of the brush pressure springs. Contaminated rings should be wiped with a clean rag, burnt rings should be cleaned with glass paper, a worn brush should be replaced with a new one and rubbed over the ring.

III. GENERATOR DIAGNOSTICS

Diagnosing generators comes down to checking the limiting voltage and functionality of the generator. To perform this operation, you must connect the voltmeter in parallel with the current consumers. The limiting voltage is checked with current consumers turned on (sidelights and side lights) and an increased engine speed. It should be in the range of 13.5-14.2 V. The performance of the generator is assessed by the voltage when all consumers are turned on at a rotation speed corresponding to the full output of the generator, which must be at least 12 V. However, such a testing technique cannot identify characteristic, although and rare generator malfunctions, such as a break or short circuit of the stator windings to ground, a break or breakdown of rectifier diodes, due to significant reserves of generator performance.

These faults are easily identified by the characteristic appearance of oscillograms, associated primarily with an increase in the range of voltage fluctuations. When the generator is working properly, the range of voltage fluctuations in the network does not exceed 1-1.2 V, which is determined by the periodic inclusion of the primary winding of the ignition coil in the load circuit. This can be easily read from the oscillogram of a motor tester (Elkon S-300, Elkon S-100A, K-461, K-488).

With one broken (shorted) diode, as a result of its rectifying properties, the range of voltage fluctuations increases to 2.5-3 V with a general decrease in the frequency of its oscillations. The average voltage level shown by the voltmeter does not change, however, voltage surges lead to a decrease in the durability of the battery and other elements of electrical equipment (V.L. Rogovtsev, “Design and operation of motor vehicles,” p. 391).

Thus, the simultaneous use of an oscilloscope and a voltmeter allows you to quickly and objectively diagnose generators and relay regulators alternating current. Increasing the generator voltage by 10-12% more than the rated voltage reduces the battery life by 2-3 times.

A faulty generator is replaced or repaired in an electrical shop, the limiting voltage of the relay-regulator is adjusted by the tension of the armature spring, and if this is not possible, the relay-regulator is also replaced. Contactless transistor relay regulators regulate only in electrical shop conditions.

29 ELECTRICAL GENERATORS ALTERNATING CURRENT

Scientific areas in which research has proven to be as fruitful as in the field of high-frequency currents are few in number. The unique properties of these currents and the amazing nature of the phenomena they demonstrated immediately captured everyone's attention. Scientists showed interest in research in this area, engineers became interested in the prospect of their industrial application, and doctors saw in them a long-awaited means of effectively treating bodily diseases. Since my first research papers were published in 1891, hundreds of volumes have been written on this subject, and countless conclusions have been drawn in connection with this new phenomenon. Nevertheless, this scientific and technological direction is in its infancy, and the future holds in its depths something incomparably more significant.

I was aware from the very beginning of the urgent need for efficient instruments to meet the rapidly increasing demands, and within eight years, consistently fulfilling the promises previously made, I have developed no less than fifty types of alternating current converters, or electric generators, perfect in every respect and carried to such an extent perfection, that even now none of them could make any significant improvements. If I had been guided by practical considerations, perhaps I would have opened a magnificent and profitable business, providing significant services to humanity along the way. But the force of circumstances and previously unprecedented prospects for even greater achievements directed my efforts in a different direction. And now everything is going to the point that soon devices will be sold on the market that, oddly enough, were created twenty years ago!

These generators are specifically designed to operate in DC and AC lighting networks, creating damped and undamped oscillations with frequency, amplitude and voltage set over a wide range. They are compact, self-contained, do not require maintenance for a long time and will be considered very convenient and useful in various fields, for example, for wireless telegraph and telephone; for converting electrical energy; for the formation of chemical compounds by fusion and addition; for gas synthesis; for ozone production; for lighting, welding, sanitary prevention and disinfection of municipal, medical and residential premises, as well as for many other purposes in scientific laboratories and industrial enterprises. Although these converters have never before been described, the general principles of their construction are fully set forth in my publications and patents, more fully dated September 22, 1896, and it is therefore thought that the several accompanying photographs and the accompanying brief explanation will provide complete information if one will be required.

The main parts of such a generator are a capacitor, a self-induction coil for accumulating high potential, a chopper and a transformer, which is powered by periodic discharges of the capacitor. The device includes at least three, and usually four, five or six adjustment elements; Efficiency adjustment is carried out in several ways, most often using a simple adjustment screw. Under favorable conditions, an efficiency of up to 85% can be achieved, meaning that the energy supplied by the power supply can be regenerated in the secondary circuit of the transformer. While the main advantage of an apparatus of this type is clearly due to the remarkable capabilities of the condenser, certain specific qualities are the consequence of the formation of a series circuit, provided that precise harmonic relationships are observed and frictional and other losses are minimized, which is one of the main objects of this project.

Generally speaking, instruments may be divided into two classes: one in which the circuit breaker has solid contacts, and the other in which the making and breaking are effected by means of mercury. Illustrations 1 to 8 inclusive show the first type, and the rest show the second. The former are able to achieve higher efficiency, taking into account the fact that losses from making and breaking are reduced to a minimum, and the transient resistance causing oscillation damping is low. The latter are preferable to use in cases where high output power and big number openings per second. the motor and the breaker consume, of course, a certain amount of energy, the share of which, however, will be less, the greater the power of the installation.

Illustration 1 shows one of the first types of generators built for experimental purposes. The capacitor is placed in a rectangular box made of mahogany, on which a self-induction coil is mounted, the turns of which, I emphasize, are divided into two sections connected in parallel or in series depending on the supply voltage of 110 or 220 volts. Four copper rods protrude from the box with a plate fixed on them with spring contacts and adjusting screws; Above the box there are two massive terminals connected to the primary winding of the transformer. Two rods are intended for connection to the capacitor, and the other two are used to connect to the switch terminals in front of the self-induction coil and the capacitor. The primary winding of the transformer consists of several turns of copper tape, to the ends of which short pins are soldered, exactly corresponding to the terminals intended for them. The secondary winding consists of two parts, wound in such a way as to reduce its own capacitance as much as possible and at the same time enable the coil to withstand a very high voltage between its terminals in the center, which are connected to terminals on two projecting rubber posts. The order of the connections in the circuit may vary somewhat, but generally they are as shown schematically in the May issue of the Electrical Experimenter on page 89, which deals with my transformer intended for use in alternating current generators, a photograph of which appears on page 16 of the same magazine numbers. The operating principle of the device is as follows. When the switch is turned on, current from the power source rushes through the self-induction coil, magnetizing the iron core inside it and disconnecting the breaker contacts. the induced current charges the capacitor to a high voltage, and after the contacts are closed, the accumulated energy is discharged through the primary winding, causing a long series of oscillations which excite the tuned secondary winding.

Il. 1. Generator created for experimental purposes

The device turned out to be extremely useful in conducting all kinds of laboratory experiments. For example, when studying impedance phenomena, the transformer was removed and a bent copper plate was connected to the terminals. The plate was often replaced by a large annular coil to demonstrate the phenomena of induction at a distance, that is, the ability to excite resonant circuits used in various studies and measurements. A transformer suitable for any application can be easily manufactured and connected to any inputs, thereby achieving great savings in time and labor. Contrary to assumptions, the state of the breaker contacts did not cause much trouble, despite the fact that the strength of the current passing through them was large, that is, in the presence of resonance, a strong current arose only when the circuit was closed, and the possibility of the formation of a destructive arc was excluded. Initially I used platinum and iridium contacts, later replaced the material with meteorite material and finally settled on tungsten. The latter brought the most satisfaction, since it allowed continuous work for many hours and days.

Illustration 2 shows a small generator designed for some special purposes. The development was based on the idea of obtaining high energies in a very short period of time after a relatively long pause. For this purpose, a coil with high self-inductance and a chopper were used fast acting. Thanks to this construction, the capacitor was charged to a high potential. In the secondary winding, fast alternating current and large spark discharges were obtained, suitable for welding thin wires, for illuminating incandescent lamps, for igniting explosive mixtures and other similar applications. This apparatus was also adapted to be powered by batteries, and this modification proved very effective as an igniter for gas engines, for which patent number 609250, dated August 16, 1898, was granted to me. Illustration 3 represents a large first-class generator designed for experiments in wireless transmission, X-ray production, and other scientific research. It consists of a box and two capacitors placed inside it, having such a capacity that the charging coil and transformer can withstand. The circuit breaker, manual switch and connecting terminals are mounted on the front panel of the self-induction coil in the same way as one of the contact springs. The capacitor body has three terminals, of which the two extreme ones serve only for connection, while the middle one is equipped with a contact plate with a screw for adjusting the interval during which the circuit is closed. The vibrating spring, whose sole function is to cause periodic openings, can be adjusted by varying its degree of compression, as well as its distance from the iron core located in the center of the charging coil, by means of four adjusting screws, which are visible in top panel, which provides any desired mechanical tuning mode. The primary winding of the transformer is made of copper strip, and terminals are made at appropriate points to vary the number of turns arbitrarily. Just as in the oscillator shown in Illustration 1, the self-induction coil has a two-section winding so that the device can operate from a mains voltage of 110 and 220 volts; several secondary windings were also provided, corresponding to waves of different lengths in the primary winding. The output power was approximately 500 watts with a damped oscillation of approximately 50,000 cycles per second. Continuous oscillations appeared for short periods of time when the vibration spring, which was pressed tightly against the iron core, was compressed, and when the contacts were disconnected using an adjusting screw, which also served as a key. With the help of this generator I made a number of important observations, and it was one of these machines that was presented at a lecture at the New York Academy of Sciences in 1897.

Il. 2. Small Tesla Oscillator Designed as an Igniter for Gas Engines

Il. 3. Large Tesla Oscillator Designed for Wireless Transmission Experiments

Il. 7 . Large Tesla transformer

Il. 8. Rotary chopper converter used for wireless transmission experiments

Illustration 4 shows a type of transformer identical in all respects to that presented in the already mentioned May 1919 issue of the Electrical Experimenter. It consists of the same basic parts, placed in a similar manner, but it is specifically designed for power sources from 220 to 500 volts and above. The adjustment is done by installing the contact spring and moving the iron core up and down inside the induction coil using two adjustment screws. To prevent damage from short circuit The power line contains fuses. During photography, the device operated, generating continuous oscillations from a 220-volt lighting network.

Figure 5 represents a later modification of the transformer, intended primarily to replace Ruhmkorff coils. In this case, a primary winding with a significantly larger number of turns is used, and the secondary is located in close proximity to it. the currents generated in the latter, with a voltage of 10,000 to 30,000 volts, are usually used to charge capacitors and power an autonomous high-frequency coil. The control mechanism is designed slightly differently, but both parts - the core and the contact spring - are adjustable, as before.

Illustration 6 shows a small device from a series of such devices, intended, in particular, for the production of ozone or disinfection. For its size it is highest degree efficient and can be connected to a voltage of 110 or 220 volts DC or alternating current, the first is preferable.

Il. 9. Transformer and mercury breaker

Il. 10. Large Tesla converter with sealed chamber and mercury controller

Illustration 7 shows a larger transformer in this series. Design and layout components remained the same, but there are two capacitors in the case, one of which is included in the coil circuit, as in previous models, while the other is connected in parallel to the primary winding. Thus, high currents are formed in the latter and, consequently, the effects in the secondary circuit are enhanced. The introduction of an additional resonant circuit also gives other advantages, but tuning is more difficult, and it is therefore desirable to use an apparatus of this kind to obtain currents of a given constant frequency.

Il. 11. Tesla generator with hermetically sealed mercury breaker, designed for low voltage generators

Il. 13. Another type of converter alternating current with hermetically sealed mercury breaker

Il. 14. Diagram and layout of parts of the model shown in illustration 13

Figure 8 shows a transformer with a rotary chopper. The case contains two capacitors of the same capacity, which can be connected in series or in parallel. The charging inductors take the form of two long bobbins on which two terminals of the secondary circuit are placed. To operate a specially designed breaker, a small DC motor is used, the speed of which can vary widely. In other respects this generator is similar to the model shown in Illustration 3, and from the above it is easy to understand how it works. This transformer was used by me in experiments on wireless transmission and often for illuminating the laboratory with my vacuum tubes, and was also exhibited during the above-mentioned lecture which I gave before the New York Academy of Sciences.

Now let's move on to the second class of machines, one of which is the alternating current converter shown in Illustration 9. Its circuit includes a capacitor and a charging induction coil, which are placed in one chamber, a transformer and a mercury chopper. The design of the latter was first described in my patent No. 609251 dated August 16, 1898. it consists of a hollow drum driven by an electric motor with a small amount of mercury inside it, which is thrown by centrifugal force onto the walls of the cavity and carries with it a contact disk that periodically closes and opens the capacitor circuit. Using the adjusting screws above the drum, you can change the depth of immersion of the blades at will, and therefore the duration of each contact, and thus adjust the characteristics of the breaker. This type of breaker satisfied all the requirements, as it worked properly with currents from 20 to 25 amperes. The number of interrupts per second was typically between 500 and 1000, but higher rates were possible. The entire unit measures 10" x 8" x 10" and has a power output of approximately 1/2 kW.

In the converter described here, the chopper is exposed to the atmosphere and gradual oxidation of the mercury occurs. The device shown in Illustration 10 is free from this drawback. It has a perforated metal case, inside of which a capacitor and a charging induction coil are located, and above it there is a chopper motor and a transformer.

Il. 15 and 16. Tesla converter with hermetically sealed mercury breaker, whose operation is regulated by gravity; motor and breaker assemblies

The type of mercury interrupter which will be described operates on the principle of a jet which, by pulsating, makes contact with a rotating disk within the drum. The stationary parts are secured within the chamber by a rod extending the length of the hollow drum, and a mercury seal is used to seal the chamber containing the breaker. The passage of current into the drum is carried out through two sliding rings located on top, which are connected in series with the capacitor and the primary winding. Oxygen exclusion is an undeniable improvement that eliminates metal oxidation and associated difficulties and maintains operating conditions at all times.

Illustration 11 shows a generator with a hermetically sealed mercury breaker. In this device, the fixed parts of the breaker inside the drum are mounted on a tube through which an insulated wire is passed, connected to one terminal of the switch, while the other terminal is connected to the reservoir. This made sliding rings unnecessary and simplified the design. The device is designed for generators with low voltage and frequency, which requires a relatively small current in the primary winding, and was used to excite resonant circuits.

Illustration 12 represents an improved model of the oscillator described in Illustration 10. In this model, the support rod inside the hollow drum has been eliminated and the mercury injection device is held in place by gravity. A more detailed description will be given in connection with another illustration. Both the capacitance of the capacitor and the number of turns of the primary circuit can be changed to be able to generate oscillations in several frequency modes.

Figure 13 is a photographic representation of another type of generator. alternating current with hermetically sealed mercury breaker, and Illustration 14 is a circuit diagram and arrangement of parts, which is reproduced from my patent No. 609245, dated August 16, 1898, which describes this particular device. The capacitor, induction coil, transformer and breaker are placed as before, but the latter has structural differences, which will become clear after considering this circuit. Hollow drum A connected to axis c, which is mounted with a vertical bearing and passes through a permanent field electromagnet d engine. The body is reinforced inside the drum on rolling bearings h of a magnetic substance protected by a cap b in the center of a plate-like iron ring, with pole pieces oo, on which there are spirals connected to the current R. The ring is supported by four posts, and in a magnetized state it holds the body h in one position while the drum rotates. The latter is made of steel, and the cap is better made of nickel silver, acid-blackened or nickel-plated. Body h has a short tube k, bent, as shown, to catch the liquid as it rotates and throw it onto the teeth of a disk attached to the drum. The disk is insulated, and contact between it and the external circuit is carried out through a mercury funnel. When the drum rotates rapidly, a stream of liquid metal is thrown onto the disk, thus closing and opening the contact approximately 1,000 times per second. The device operates silently and, due to the absence of an oxidizing environment, remains consistently clean and in excellent condition. It is possible, however, to achieve a much higher number of oscillations per second in order to make the currents suitable for wireless telephony, and other similar purposes.

A modified type of oscillator is shown in Illustrations 15 and 16, the first being a photographic representation and the second a diagram showing the arrangement of the internal parts of the regulator. In this case the shaft b. load-bearing hollow container A, resting on rolling bearings, connected to the spindle j. to which the load is attached k. isolated from the latter, but mechanically connected to it, bent bracket L serves as a support for the freely rotating disc of the breaker with teeth. The disk is connected to outer contour by means of a mercury funnel and an insulated plug protruding from the top of the shaft. Thanks to the inclined position of the electric motor, the load k holds the breaker disk in place by gravity, and as the shaft rotates, the circuit consisting of the capacitor and primary coil is rapidly closed and opened.

Il. 17. Tesla converter with an interrupting device in the form of a jet of mercury

Illustration 17 shows an identical apparatus in which the interrupter is a stream of mercury striking an insulated gear wheel, which is located on an insulated pin in the center of the drum cap, as seen in the photograph. The connection to the capacitor is made through brushes located on the same cover.

Figure 18 - converter type with mercury breaker using a disc modified in some details that need to be carefully considered.

Presented here are only a few of the ac converters that have been completed, and they form a small part of the high-frequency apparatus of which I hope to present a detailed description later, when I am free from pressing obligations.

Il. 18. Tesla converter with mercury breaker using a disk

Alternator

Description:

Alternator. Device and principle of operation.

Current generator is an electrical machine that converts mechanical energy into electrical energy. They can generate both direct and alternating current.

Until the second half of the 20th century DC generators were used in vehicles. Then semiconductor diodes became widespread, which made it possible to rectify alternating current or make it direct. Therefore, in this area too, DC generators have replaced more reliable and compact three-phase AC generators.

In I have examined in detail the issues of the operation of an electric motor; now the general principles of operation and the design of a current generator will be outlined. I will not dwell in detail on DC machines, because they are not used in everyday life, garages and vehicles today. They are only widely used in urban electric transport: trolleybuses and trams.

Operating principle of the current generator

The generator operates based on the law electromagnetic induction Faraday - electromotive force (EMF) is induced in a rectangular loop (wire frame) rotating in a uniform rotating magnetic field.

EMF also occurs in a stationary rectangular frame if a magnet is rotated in it.

The simplest generator It is a rectangular frame placed between 2 magnets with different poles. In order to remove the voltage from the rotating frame, slip rings are used. On practice Electromagnets are used, which are inductor coils or windings made of copper wire in electrical insulating varnish. When electric current passes through the windings, they begin to have electromagnetic properties. To excite them it is necessary additional source current - in cars it is a rechargeable battery. In domestic power plants, excitation during starting occurs as a result of self-excitation or from an additional low-power DC generator, which is driven by the generator shaft.

According to the operating principle generators can be synchronous or asynchronous.

Asynchronous generators They are structurally simple and inexpensive to manufacture, more resistant to short circuit currents and overloads. An asynchronous electric generator is ideal for powering active loads: incandescent lamps, electric heaters, electronics, electric burners, etc. But even short-term overload is unacceptable for them, therefore, when connecting electric motors, non-electronic welding machines, power tools and other inductive loads, a reserve of power should be at least three times, and preferably four times.
Synchronous generator Perfect for inductive consumers with high inrush currents. They are capable of withstanding a fivefold current overload within one second.

Alternating current generator device

As an example of a device, let’s take a three-phase automobile generator.

Car generator consists of a body and two covers with holes for ventilation. The rotor rotates in 2 bearings and is driven by a pulley. At its core, the rotor is an electromagnet consisting of one winding. Current is supplied to it using two copper rings and graphite brushes, which are connected to an electronic relay controller. It is responsible for ensuring that the voltage supplied by the generator is always within the permissible limits of 12 Volts with permissible deviations and does not depend on the pulley rotation speed. The relay regulator can be either built into the generator housing or located outside it.

The stator consists of three copper windings interconnected in a triangle. A rectifier bridge of 6 is connected to their connection points semiconductor diodes, which convert voltage from alternating to direct.

Gasoline electric generator consists of a motor and a current generator driving it directly, which can be either synchronous or asynchronous.

The engine is equipped with the following systems: starting, fuel injection, cooling, lubrication, speed stabilization. Vibration and noise are absorbed by a muffler, vibration dampers and shock absorbers.

Electricity is not a primary energy, freely present in nature in significant quantities, and in order to be used in industry and everyday life, it must be produced. Most of it is created by devices that convert driving force into electricity- this is how generators work, the sources of mechanical energy for which can be steam and water turbines, internal combustion engines and even human muscular power.

History and evolution

Michael Faraday's discovery of the laws of electromagnetic induction in 1831 became the basis for the construction of electrical machines. But before the advent of electric lighting, there was no need to commercialize the technology. Early electrical appliances, such as the telegraph, used galvanic batteries as a power source. This was a very expensive way to produce electricity.

At the end of the 19th century, many inventors sought to use Faraday's principle of induction to generate electricity mechanically. Some important achievements were the development of the dynamo by Werner von Siemens and the production by Hippolyte Fontaine of working models of Theophilus Gram's generators. The first devices were used in conjunction with external arc lighting devices, known as Yablochkov candles.

They were replaced by Thomas Edison's highly successful incandescent lamp system. Its commercial power plants were based on powerful generators, but the circuit, built on direct current production, was poorly suited for distributing power over long distances due to impressive heat losses.

Nikola Tesla developed an improved alternating current generator as well as a practical induction motor. These electrical machines, along with step-up and step-down transformers, provided the basis for electric companies to build larger distribution networks using large power plants. In large AC power systems, generation and transportation costs were several times lower than in Edison's scheme, which stimulated the demand for electricity and, as a consequence, the further evolution of electric machines . The main dates in the history of generators can be considered:

Principle of operation

Generators operating on the principle of electromagnetic induction do not create electricity. Using mechanical energy, they only set in motion the electrical charges that are always present in conductors. The operating principle of an electric generator can be compared to a water pump, causing a flow of water, but not creating water in the pipes. Overwhelming Most induction generators are rotary type electric machines, consisting of two main components:

stator (fixed part);
rotor (rotating part).

To illustrate how an electric generator works, a simple electrical machine consisting of a coil of wire and a U-shaped magnet can be used. The main fundamental elements of this model:

a magnetic field;
movement of a conductor in a magnetic field.

A magnetic field is the area around a magnet where its strength is noticeable. To better understand how the model works, you can imagine the lines of force coming out from the north pole of the magnet and returning to the south. The stronger the magnet, the more lines of force it creates. If the coil begins to rotate between the poles, then both its sides will begin to intersect imaginary magnetic lines. This causes the movement of electrons in the conductor (generation of electricity).

In accordance with the right-hand rule, when the coil rotates, a current will be induced in it, changing its direction every half turn, since the lines of force by the sides of the coil will intersect in one direction or the other. Twice for each revolution the coil passes through positions (parallel to the poles) at which electromagnetic induction does not occur. Thus, the simplest generator works like an electrical machine that produces alternating current. The voltage it creates can be changed by:

magnetic field strength;
coil rotation speed;
the number of turns of wire crossing the magnetic field lines.

A coil of conductor turning between the poles of a magnet creates another important effect. When current flows in the coil, it creates an electromagnetic field that is opposite to the field of a permanent magnet. And the more electricity is induced in the coil, the stronger the magnetic field and the resistance to turning the conductor. The same magnetic force in the turns causes rotation of the electric motor rotor, that is, under certain conditions, generators can work as motors and vice versa.

Features of AC Generators

Alternating current (AC) is produced by the simple generator described. In order for the generated electricity to be used, it must be somehow delivered to the load. This is done using a contact unit on the shaft, consisting of rotating rings and fixed carbon parts called brushes sliding along them. Each end of the rotating conductor is connected to a corresponding ring, and the current thus created in the turn passes through the rings and brushes to the load.

Structure of industrial machines

Practical generators differ from the simplest ones. They are usually equipped with an exciter - an auxiliary generator that supplies direct current to the electromagnets used to create a magnetic field in the generator.

Instead of a turn in the simplest model, practical devices are equipped with windings made of copper wire, and the role of a magnet is performed by coils on iron cores. In most alternators, electromagnets that produce the alternating field are placed on the rotor and electrical energy is induced in the stator coils.

In such devices, a collector is used to transfer direct current from the exciter to the magnets. This greatly simplifies the design, since it is more convenient to transmit weak currents through the brushes and receive high voltage from the stationary stator windings.

Applications in networks

In some machines, the number of winding sections coincides with the number of electromagnets. But most AC generators are equipped with three sets of coils for each pole. Such machines produce three streams of electricity and are called three-phase. Their power density is significantly higher than that of single-phase ones.

In power plants, AC generators serve as converters of mechanical energy into electrical energy. This is because AC voltage can be easily increased or decreased using a transformer. Large generators produce voltages of about 20 thousand volts. It is then increased by more than an order of magnitude to allow electricity to be transported over long distances. At the point where the electricity is used, a usable voltage is created using a series of step-down transformers.

Dynamo design

A coil of wire rotating between the poles of a magnet changes the poles at the ends of the conductor twice for each revolution. To turn a simple model into a DC generator, you need to do two things:

divert current from the coil to the load;
organize the flow of diverted current in only one direction.

The role of the collector

A device called a collector can accomplish both tasks. Its difference from a contact brush assembly is that its basis is not a ring of conductor, but a set of segments isolated from each other. Each end of the rotating circuit is connected to the corresponding sector of the commutator, and two stationary carbon brushes remove electric current from the commutator.

The collector is designed in such a way that, regardless of the polarity at the ends of the turn and the phase of rotation of the rotor, the contact group provides the current with the desired direction when transmitting it to the load. The windings in practical dynamos consist of many segments, therefore, for DC generators, due to the need to switch them, a circuit in which an armature with induced coils rotates in a magnetic field turned out to be preferable.

Power supply for electromagnets

Classic dynamos use a permanent magnet to induce the field. The remaining DC generators require power for the electromagnets. For this purpose, so-called separately excited generators use external sources direct current. Self-exciting devices use some of the self-generated electricity to control electromagnets. Starting such generators after shutdown depends on their ability to accumulate residual magnetism. Depending on the method of connecting the field coils to the armature windings, they are divided into:

shunt (with parallel excitation);
serial (with sequential excitation);
mixed excitation (with a combination of shunt and series).

Excitation types are used depending on the voltage control required. For example, generators used to charge batteries require simple operation tension. In this case, the appropriate type would be a shunt. A separately excited generator is used as machines that generate energy for a passenger elevator, since such systems require complex control.

Application of collector generators

Many DC generators are driven by AC motors in combinations called motor-generator sets. This is one of the ways to change alternating current to direct current. Plants performing galvanization, producing aluminum, chlorine and some other materials by electrochemical method, need large quantities direct current.

Diesel electric generators are also used to supply DC power to locomotives and ships. Since commutators are complex and unreliable devices, DC generators are often replaced by machines that produce AC combined with electronic ones. Switch generators have found application in low-power networks, allowing the use of permanent magnet dynamos without excitation circuits.

There are other types of devices that are capable of producing electricity. These include electrochemical batteries, thermoelectric and photovoltaic cells, and fuel converters. But compared to AC/DC induction generators, their share in global energy production is negligible.

Electric generator– one of the constituent elements of an autonomous power plant, as well as many others. In fact, it is the most important element, without which the generation of electrical energy is impossible. An electric generator converts rotational mechanical energy into electrical energy. The principle of its operation is based on the so-called phenomenon of self-induction, when an electromotive force (EMF) arises in a conductor (coil) moving in the magnetic field lines, which can (for better understanding question) called electrical voltage (although this is not the same thing).

The components of an electric generator are a magnetic system (mainly electromagnets are used) and a system of conductors (coils). The first creates a magnetic field, and the second, rotating in it, converts it into an electric one. Additionally, the generator also has a voltage removal system (commutator and brushes, connecting the coils in a certain way). It actually connects the generator with electrical consumers.

You can get electricity yourself by carrying out the simplest experiment. To do this, you need to take two magnets of different polarities or turn two magnets with different poles towards each other, and place a metal conductor in the form of a frame between them. Connect a small (low-power) light bulb to its ends. If you start to rotate the frame in one direction or another, the light bulb will begin to glow, that is, at the ends of the frame a electrical voltage, and an electric current flowed through its spiral. The same thing happens in an electric generator, the only difference is that the electric generator has a more complex system of electromagnets and a much more complex coil of conductors, usually copper.

Electric generators differ both in the type of drive and in the type of output voltage. By type of drive that sets it in motion:

Turbogenerator – driven by a steam turbine or gas turbine engine. Mainly used in large (industrial) power plants.
Hydrogenerator – driven by a hydraulic turbine. It is also used in large power plants operating through the movement of river and sea water.
Wind generator – driven by wind energy. It is used both in small (private) wind power plants and in large industrial ones.
The diesel generator and gasoline generator are driven by a diesel and gasoline engine, respectively.

By type of output electric current:

DC generators - the output is direct current.
Alternating current generators. There are single-phase and three-phase, with single-phase and three-phase AC output respectively.

Different types of generators have their own design features and practically incompatible components. What unites them only general principle creating an electromagnetic field by mutual rotation of one system of coils relative to another or relative to permanent magnets. Due to these features, repair of generators or their individual components Can only be done by qualified specialists.