Detailed information of electromagnet

Electromagnet is a device that generates electromagnetism when it is electrified. A conductive winding matching its power is wound around the outside of the iron core. This electrified coil is as magnetic as a magnet, also called an induction cooker. We usually make it into a strip or hoof shape to make the iron core easier to magnetize. In addition, in order to demagnetize the electromagnet immediately after power failure, we often use soft iron or silicon steel materials with faster demagnetization speed. Such an electromagnet is magnetic when it is energized and disappears when it is de-energized. Electromagnet is widely used in our daily life, and the power of generator is greatly improved because of its invention.

Chinese name: electromagnet mbth: electromagnetics discipline: physics, electromagnetic principle: classification of electromagnetic force generated after electrification: 1. Ac electromagnet 2. Relevant persons of DC electromagnet: Oster's introduction, principle, classification, current classification, use classification, direction judgment, advantages, classification, history, nature, significance, precautions, use of electromagnet, manufacturing principle, reasons for loss of excitation, sources of magnetic energy, loss of excitation hazards and comparison with permanent magnets. Electromagnet is a device that generates electromagnetism when it is electrified. A conductive winding matching its power is wound around the outside of the iron core. This electrified coil is as magnetic as a magnet, also called an induction cooker. We usually make it into a strip or hoof shape to make the iron core easier to magnetize. In addition, in order to demagnetize the electromagnet immediately after power failure, we often use soft iron or silicon steel materials with faster demagnetization speed. Such an electromagnet is magnetic when it is energized and disappears when it is de-energized. Electromagnet is widely used in our daily life, and the power of generator is greatly improved because of its invention. Principle When the iron core is inserted into the energized solenoid, the iron core is magnetized by the magnetic field of the energized solenoid. The magnetized iron core also becomes a magnet, so the magnetism of the solenoid is greatly enhanced by the superposition of two magnetic fields. In order to make the electromagnet more magnetic, the iron core is usually made into a hoof shape. However, it should be noted that the winding direction of the coil on the horseshoe iron core is opposite, one side is clockwise, and the other side must be counterclockwise. If the winding direction is the same, the magnetization of the two coils on the iron core will cancel each other, making the iron core non-magnetic. In addition, the iron core of electromagnet is made of soft iron, not steel. Otherwise, once the steel is magnetized, it will remain magnetic for a long time and cannot be demagnetized, and its magnetic field strength cannot be controlled by current, thus losing the advantage of electromagnet. Electromagnet Electromagnet is a device that generates magnetic force through current. It is a non-permanent magnet, and its magnetism is easy to start or eliminate. For example, large cranes use electromagnets to lift abandoned vehicles. When current passes through a wire, a magnetic field will be generated around the wire. Using this characteristic, when current passes through the solenoid, a uniform magnetic field will be generated in the solenoid. If a ferromagnetic substance is placed in the center of the solenoid, the ferromagnetic substance will be magnetized and the magnetic field will be greatly enhanced. Generally speaking, the magnetic field generated by electromagnet is related to current, the number of coils and the ferromagnetic body in the center. When designing electromagnets, we will pay attention to the distribution of coils and the selection of ferromagnets, and control the magnetic field with current. Due to the resistance of coil material, the magnetic field generated by electromagnet is limited, but with the discovery and application of superconductor, it will have the opportunity to exceed the existing limitations. Classification by current: 1. Ac electromagnet 2. DC electromagnet: 1. Brake electromagnet: used as a mechanical brake of motor in electric transmission device to achieve the purpose of accurate and rapid stop. The common models are MZD 1 (single phase) and MZS 1 (three phase) series. 2. Lifting electromagnet: used as lifting equipment to lift magnetic materials such as steel and iron ore, or used as electromagnetic manipulator to clamp magnetic materials such as steel. 3. Valve electromagnet: the magnetic valve is driven by magnetic force, so as to open, close or change the valve port. 4. Traction electromagnet: The traction mechanism is mainly used to perform automatic control tasks. Judging the direction of the magnetic field of an electromagnet can be judged by Ampere's law. Ampere rule is a rule that expresses the relationship between current and the direction of magnetic induction line of current-excited magnetic field, which is also called right-handed spiral rule. (1) Ampere's Law in the electrified straight wire (Ampere's Law 1): Hold the electrified straight wire with your right hand, with your thumb pointing in the direction of current and your four fingers pointing in the direction of magnetic field lines around the electrified straight wire. (2) Ampere rule in the energized solenoid (Ampere rule 2): Hold the energized solenoid with the right hand, so that the four fingers bend in the same direction as the current, then the end pointed by the thumb is the N pole of the energized solenoid. Advantages electromagnets have many advantages: the magnetism of electromagnets can be controlled by on-off current; The magnitude of magnetic force can be controlled by the intensity of current or the number of turns of coil; The magnetic field can also be controlled by changing the resistance to control the current; Its magnetic pole can be controlled by changing the direction of current, and so on. That is, the strength of magnetism can be changed, the presence or absence of magnetism can be controlled, the direction of magnetic poles can be changed, and magnetism can disappear due to the disappearance of current. Electromagnet is an application of current magnetic effect, which is closely related to life, such as electromagnetic relay, electromagnetic crane, maglev train, electronic door lock, intelligent channel turning, electromagnetic flowmeter and so on. Classification electromagnet can be divided into DC electromagnet and AC electromagnet. If electromagnets are classified according to their uses, they can be mainly divided into the following five types: (1) traction electromagnets-mainly used to pull mechanical devices, open or close various valves and perform automatic control tasks. (2) Lifting electromagnet-lifting equipment used for lifting ferromagnetic materials such as steel ingots, steel products and iron sands. (3) Brake electromagnet-mainly used for braking the motor to achieve the purpose of accurate parking. (4) the electromagnetic system of automatic electrical appliances ── such as electromagnetic relay and contactor, electromagnetic release of automatic switch and operating electromagnet, etc. (5) Electromagnets for other purposes ── such as electromagnetic sucker of grinder and electromagnetic vibrator. As early as the spring of 1820, Oster of Denmark stumbled upon this principle. 1822, French physicists arago and Wojciech Luczak found that when current passes through a winding with iron blocks, the iron blocks in the winding can be magnetized. This is actually the first discovery of the principle of electromagnet. 1823, sturgeon did a similar experiment: he wound 18 turns of bare copper wire on a U-shaped iron bar that was not a magnetic bar. When the copper wire is connected to the photovoltaic cell, the copper coil wound on the U-shaped iron bar generates a dense magnetic field, thus turning the U-shaped iron bar into an "electromagnet". The magnetic energy of this electromagnet is magnified many times than that of a permanent magnet, and it can absorb iron 20 times heavier than it. When the power supply is cut off, the U-shaped iron bar can't absorb any iron and becomes an ordinary iron bar. Sturgeon's invention of electromagnet made people see the bright future of converting electric energy into magnetic energy, which soon spread in Britain, the United States and some coastal countries in Western Europe. 1829, Henry, an American electrician, made some innovations to the sturgeon electromagnet device, replacing the bare copper conductor with a magnetoelectric insulated conductor, so as not to worry about being short-circuited by the copper conductor. Because of the insulating layer, the wires can be tightly wound together. The denser the coils, the stronger the magnetic field, which greatly improves the ability of converting electric energy into magnetic energy. By 183 1, Henry has developed a newer electromagnet. Although it is small, it can absorb 1 ton of iron. Inspired by a series of experiments such as Oster's current magnetic effect experiment, Ampere realized that the essence of magnetic phenomenon is current, and attributed all kinds of interactions involving current and magnet to the interaction between currents, and put forward the basic problem of finding the interaction law of current elements. In order to overcome the difficulty that isolated current elements can not be measured directly, Ampere carefully designed four zero-indicating experiments after careful theoretical analysis, and obtained the results. However, due to the concept of over-distance action of ampere on electromagnetic action, the assumption that the force between two current elements follows the connecting line is imposed in theoretical analysis, and Newton's third law is expected to be obeyed, which makes the conclusion wrong. The above formula is a modified result, which abandons the assumption that the wrong force is along the line. It should be understood from the point of view of short-distance action that one current element generates a magnetic field and the magnetic field exerts a force on another current element. Ampere's law of linear current also applies to short-term linear current. Annular current can be regarded as many small linear currents, and for each small linear current, the direction of magnetic induction intensity on the central axis of annular current can be determined by ampere rule of linear current. The direction of the magnetic induction line on the central axis of the annular current is obtained by superposition. Ampere rule of linear current is basic, and ampere rule of annular current can be deduced from ampere rule of linear current. The ampere rule of linear current is also applicable to the magnetic field generated by the linear motion of charge. At this time, the current direction is the same as the positive charge direction, but opposite to the negative charge direction. Meaning Ampere's law is equivalent to Coulomb's law, and it is the basic experimental law of magnetic action. It determines the properties of the magnetic field and provides a method to calculate the current interaction. Pay attention to electromagnet: a device that uses the magnetic effect of current to make soft iron (the inner mandrel of electromagnet coil, which can quickly magnetize and demagnetize) magnetic. WEISTRON electromagnet (1) Insert the soft iron bar into the spiral coil. When the coil is energized, the magnetic field inside the coil magnetizes the soft iron bar into a temporary magnet, but when the current is cut off, the magnetism of the coil and the soft iron bar disappears. (2) The magnetic field generated by the magnetization of the soft iron bar, together with the magnetic field in the primary coil, greatly enhances the total magnetic field intensity, so the magnetic force of the electromagnet is greater than that of the natural magnet. (3) The greater the current of the solenoid coil, the more turns of the coil and the stronger the magnetic field of the electromagnet. Application of Electromagnet (1) Crane: It is a powerful electromagnet used in industry, which can be used to lift steel plates, containers, scrap iron, etc. (2) Telephone: The next section introduces. (3) ammeter, voltmeter, ammeter (4) electric bell, etc. (5) Automation control equipment (6) Industrial automation control and office automation. (7) Packaging machinery, medical instruments, food machinery, textile machinery, etc. (8) Electromagnetic relay (9) Manufacturing principle of maglev train 1. The direction of the magnetic field leading to the center of the circular coil of current (1) can be regarded as a straight line, which is determined by the ampere's right-hand rule. (2) The magnetic field generated by each short-circuit current on a circular coil with current is in the same direction, so the magnetic field in the coil is stronger than that generated by a straight current. (3) When a current is applied to a circular wire, the magnetic field outside the coil is different from that generated by each small current, so the synthesized magnetic field is weaker than that inside the coil. (4) The greater the current of a circular coil, the smaller the radius and the greater the magnetic field intensity in the center of the coil. (5) The magnetic lines of the circular coil and the disc-shaped thin magnet are similar in shape. 2. The magnetic field of spiral coil current (1) is wound into a spiral long coil by a long wire, which is equivalent to connecting many circular coils in series. The magnetic field established in the center of each circular wire is in the same direction, which can enhance the effect, so the magnetic field in the center of the coil is stronger than that in a single-turn circular coil. (2) The magnetic field lines in the coil form a straight line with the same direction, and the magnetic field lines at the left and right ends of the coil gradually bend outward. (3) The characteristics of magnetic field lines of spiral coils are similar to that of bar magnets, and the magnetic field lines in the coils are just opposite to those outside the coils. (4) The intensity of the magnetic field in the coil is directly proportional to the current on the coil and the number of coils per unit length. 3. Right-handed spiral law of magnetic field direction in spiral coil current (Ampere's theorem): Hold the coil with the right hand, with four fingers pointing in the direction of current, and the direction pointed by the thumb is the direction of magnetic field lines in the coil. Loss of excitation leads to the generator not being used for a long time, which leads to the loss of residual magnetism contained in the iron core before leaving the factory, and the excitation coil cannot establish its due magnetic field. At this time, the engine runs normally but can't generate electricity, which is a new phenomenon. Or there are many units that have not been used for a long time. Treatment: 1) Press the excitation button, 2) Magnetize the battery without the excitation button, 3) Load the light bulb and overspeed for several seconds. Although the magnetic energy generator with low shaft resistance can only convert about 50% of the negative torque magnetic energy into positive torque magnetic energy in principle design, the positive torque generated is enough to offset the negative torque (because it is practically impossible to convert all the negative torque magnetic energy into positive torque magnetic energy). After further research and analysis of the structure and working principle of conventional generators, we finally found a breakthrough, that is, on the basis of the structure of conventional power generation principles, we use the "energy buffer transfer method" to achieve the above goals; That is to say, some induced currents with fixed directions are temporarily processed and then released in a lag time. The released energy can not only be continuously output to the load, but also the additional magnetic energy generated in the armature flywheel winding can do positive work (generate positive torque) on the rotor. This is the source of positive torque magnetic energy of low shaft resistance generator. Loss of excitation hazard generator loss of excitation fault refers to the sudden disappearance of all or part of the excitation of the generator. The reasons of loss of excitation include rotor winding fault, exciter fault, automatic de-excitation switch false trip, damage of some components in semiconductor excitation system or circuit fault, misoperation, etc. Due to asynchronous operation, the mechanical speed of generator rotor is higher than synchronous speed. Due to slip, the stator winding current increases, and the rotor winding generates induced current, which leads to additional heating of the stator and rotor windings. The analysis shows that the generator loss of excitation will cause different degrees of harm to the power system and the generator itself, which can be summarized as follows. Harm to the generator itself: (1) After demagnetization of the generator, the magnetic leakage at the stator end increases, which makes the end parts and the end core overheat. (2) After asynchronous operation, the equivalent reactance of the generator decreases from to. Therefore, the reactive power absorbed from the system increases and the stator winding is overheated. (3) The difference frequency current in the generator rotor winding produces extra loss in the rotor winding, which leads to the rotor winding heating. (4) Large-scale direct cooling turbogenerator has small maximum average asynchronous torque, relatively low inertia constant, and obvious asymmetry between longitudinal axis and transverse axis of rotor. For these reasons, the torque and active power of loss-of-excitation generator will swing violently under heavy load. This effect is more serious for hydro-generators. Harm to power system: (1) After generator loss of excitation, adjacent normal generators may lose synchronization with the system due to active power swing and system voltage reduction, causing system oscillation. (2) generator loss of excitation leads to a large number of reactive power shortage in the system. When the reactive power reserve in the system is insufficient, the voltage will drop. In severe cases, it will cause voltage collapse and system collapse. (3) When one generator loses excitation, the voltage drops, and other generators in the system increase reactive power output under the action of automatically adjusting excitation devices. Some generators, transformers and transmission lines are over-current, and the backup protection may be over-current, which expands the fault range. Compared with permanent magnets, both permanent magnets and electromagnets can generate different forms of magnetic fields. When choosing a magnetic circuit, the first thing to consider is the work you need a magnet to do. In the case of inconvenient electricity use, frequent power failure or no need to adjust magnetic force, permanent magnets are dominant. Electromagnets are beneficial to applications that need to change the magnetic force or remote control. Magnets can only be used in the original predetermined way. If the wrong type of magnet is used for special purposes, it may be very dangerous and even fatal. Many machining operations are carried out on heavy bulk materials, and these applications require permanent magnets. Many users in machinery factories think that the biggest advantage of these magnets is that they don't need wires. The permanent magnet is characterized by a lifting capacity of 330~ 10000 lbs, and the magnetic circuit can be connected or disconnected only by turning a handle. Magnets are generally equipped with safety locks to ensure that magnets will not be accidentally detached during lifting. The magnet group can be used for long loads that are relatively heavy and cannot be handled by a single magnet. In addition, in many cases, the parts to be processed are very thin (0.25 inch or less) and must be taken out from a pile of similar parts. Permanent magnets are not suitable for lifting only one piece from a pile of parts at a time. Although permanent magnets are extremely reliable when used correctly, they cannot change the magnetic force. In this respect, the electromagnet enables the operator to control the magnetic field strength through the variable voltage control device and to select one from the stacked components. The self-contained electromagnet is the magnet with the highest cost performance per unit lifting capacity, and the lifting capacity can be extended to 10500 lbs. Magnets powered by batteries are useful. They use their own colloidal batteries to increase their lifting capacity and can handle flat, round and component-shaped products. Magnets powered by batteries can repeatedly complete the lifting action, providing considerable lifting capacity without external power supply.