The era of electrification began not so long ago and in a couple of centuries completely changed our lifestyle. Look around, wherever the eye falls, be sure to see some kind of electrical appliance. People are so accustomed to different machines that do almost all the work for them, that there is an illusion that it has always been like that. But let's look beyond the veil that hides from us the process of vital activity of electric friends. We will analyze the principle of operation and the device of the DC generator.
A bit of history
Electricity was observed by the ancient Greeks. The property of amber was attracted to attract different particles. People considered this a magnetism inherent in resin. But later they noticed the ability of other materials to acquire magnetism. For example, when rubbed, glass also began to attract small light elements: paper particles, hairs and dust. So it became clear that the magnetic effect arises according to some law.
Subsequently, in the XVIII century, a prototype of a modern capacitor was created, baptized by the name of the inventor "Leiden Bank". This simple mechanism was able to accumulate a charge, which at that time was considered a kind of liquid that saturates solids and can flow from one body to another at an amazing speed - for several miles in a split second.
When the atom and its constituent nucleus and electron were discovered, everything fell into place. People realized that it is the electrons that are those charges that created such inexplicable phenomena as electric discharges. But so far these were only static charges. From the experiments of Faraday and Oersted, the electricity that we know now originates. They invented a DC mock generator, the device and principle of operation of which are based on the phenomenon of electromotive force EMF.
The power of electricity
As the water of the river sets in motion the attraction of the earth, so charged particles in the conductor make EMF move. This force is closely related to the magnetic phenomenon, namely, it appears as soon as the flux created by the magnet changes. EMF is capable of working only in a substance where free charges are always available. This property is possessed by metals and saline solutions.
EMF is greater, the faster the intensity of the magnetic waves changes. As you know, a magnet always has two poles. In accordance with the direction in which the flow changes relative to the conductor, the current in the conductor flows in one direction or another. Positive and negative charges themselves create between themselves an energy field, which we call voltage, it is the greater, the stronger the total electric charge of the pole of the same name.
What is an electric generator?
A design or machine that is capable of converting any mechanical force into electrical energy is called an electricity generator. The principle of operation and the design of the DC generator are associated with magnetism. If you take a permanent magnet and cross the field of its intensity with a conductor, then in the latter there appears a force that forces charged particles to move in one direction - a current appears. The same thing will happen with a fixed conductor and a moving magnet.
Scientists have experimentally established that the greater the current, the greater:
- Magnetic flux between the poles of a magnet.
- The speed of crossing lines of tension.
- The length of the live wire.
If you move the conductor in parallel with the flow, then induction is not observed in it. The law of the right hand was derived from this, which helps to understand in which direction the current is moving. When the hand is placed on the right side of the body with the palm so that the magnetic lines of the intense field enter it, and the thumb is bent and indicates where the conductor moves, the remaining four fingers will show the current path. In a magnet, the field motion vector is directed from north to south.
Scheme of operation of an elementary generator
The principle of operation and design of a simple type direct current generator are as follows: the frame is made of current-carrying material, mounted on an axis and rotates between the poles of the magnet. Each free end of the frame is connected to its contact, having the form of an arcuate plate. Together, the contacts form a circle torn at two points (collector). These semicircular contacts are movably connected to spring-loaded conductive brushes. They remove current.
In space, the frame relative to the contacts is oriented so that when each half of the sections of the largest magnetic flux intersects, the brushes are closed at the contacts. When the elements of the frame go through the phase of movement along the lines, the brush contacts are open to the collector.
If you connect an oscilloscope, you can see that the DC generator device and principle of operation is such that it produces an alternation of half waves located on one side of the coordinates and changing their value from zero to highest and again to zero. Their repetition rate depends on the speed of rotation of the frame. This means that the current in such a system moves in one direction (constant), but has a pulsating appearance.
The principle of operation and the device of the DC generator
A real DC current generator is more complicated, although the principle of its operation is no different from that considered above. Instead of one frame and a pair of semicircular contacts, it has many frames and collector contacts. This, firstly, increases the power of such a machine, and secondly, it smooths the ripple of the current, since each frame creates its own half-wave, which, adjusting to each other, form the total current. Such a rotating system is called an anchor or rotor.
The generator magnet is also modified. Its role is played by an electromagnet consisting of a winding and a core. Using electromagnets, you can create a large magnetic flux, which is beyond the power of a regular constant. In addition, the flow rate can be easily changed. The fixed part of the generator is called the stator.
Depending on the operating mode of the machine during shaft rotation, the following processes are observed between the stator and the rotor:
- No load connected to the generator. In the case of such idle operation, the armature rotates, the EMF is induced in it, but there is no current in the winding, since the circuit is not closed.
- The DC generator, the circuit of which is connected to the circuit, operates in load mode. In this case, current flows in the anchor and a new component appears - the magnetic flux created by the anchor (reaction of the armature). This flow moves in such a direction that it counteracts the main lines of force created by the electromagnet. As a result, the real EMF will be lower, that is, the generator power is reduced. And the greater the load of the generator, the more energy is spent on overcoming the reaction of the armature during rotation of the shaft.
In order to level the magnetic flux of the armature, so-called compensation windings are introduced into the rotor circuit, in which a magnetic flux is formed that weakens the armature reaction.
Types of Constant Electricity Generators
The principle of operation and the arrangement of DC generators differ in the execution of the excitation circuit. They are:
- Magnetoelectric. They use permanent magnets to create a magnetic flux. Such machines, usually of low power, have high efficiency, since there are no losses in the field windings. The lack of devices in the complexity of regulation.
- Generators with an independent excitation circuit. These are devices whose electromagnet winding is powered from third-party power sources: a battery or a generator.
- Self-excited DC generators. Such devices feed electromagnets from their own anchor. The main condition for self-excitation is the residual magnetic flux. The design, the principle of operation of the generators and the circuit for their inclusion is compound, shunt and serial.
The principle of operation and the device of the generator from the electric motor
The principle of reversibility of electric machines suggests that any electric motor can be converted into a generator and vice versa. After all, both of these devices use induction EMF as the basis of their work. Only in the engine an electric current is supplied to the rotor, which, creating a magnetic flux, is repelled from the poles of the stator magnet, making a rotational movement.
If the motor shaft is rotated at a certain speed, induction EMF will begin to be induced in the windings of the armature and current will flow. The restriction is only in the thickness of the armature winding wire. When the wire is thin, then such a generator will not be able to get more power.
Where did the direct current source find application?
Despite the fact that constant electricity can be obtained by rectifying an alternating current, a direct current generator is widely used. The principle of operation, the scheme of such a machine are indispensable in metallurgical enterprises, in powerful electrolysis plants. In the transport industry, units operate in electric locomotives, shipping ships. For powering the exciting windings of alternating current generators at power plants, DC voltage sources are also applicable. For domestic purposes, dynamo DC machines have been developed. They can be seen on bicycles, where they feed the lights.
Conclusion
Current generators of constant polarity are good in that they can generate electricity at different speeds of rotation of the shaft. They do not need to withstand a clear frequency, as, for example, in alternators, where it should be at 50 Hz. Such machines are very convenient to use as alternative sources of electricity, for example in wind generators.