Electromagnet is a device that generates electromagnetism by energizing electricity. In the core of the external winding of its power to match the conductive winding, this current coil like a magnet with magnetic properties, it is also called electromagnet (electromag). We usually make it into a bar or hoof shape to make the core easier to magnetize. In addition, in order to make the electromagnet de-magnetize immediately after power failure, we often use soft iron or silicon steel material to make the demagnetization faster. Such an electromagnet is magnetic when energized, and the magnetism disappears after power failure. Electromagnet in our daily life has a very wide range of sets of use, because of its invention also makes the generator power has been greatly improved.
Basic introduction Chinese name ：Electromagnet Foreign name ：electromag Subject ：Physics, electromagnetism Principle ：Electricity generates electromagnetic force Classification ：1.A.C. electromagnet 2.D.C. electromagnet Related characters ：Ostor Introduction, Principle, Classification, According to the current, according to the use of points, the direction of the judgement, the advantages of the classifications, the history of the nature of the significance of the attention, the set of electromagnets, the production of the principle of the magnetism of the loss of magnetization Causes, Sources of Magnetic Energy, Hazards of Demagnetization, Comparison with Permanent Magnets, Introduction An electromagnet is a device that generates an electromagnetic force by applying electricity. In the core of the external winding of the conductive winding to match its power, this current coil has magnetic properties like a magnet, it is also called an electromagnet (electromag). We usually make it into a bar or hoof shape to make the core easier to magnetize. In addition, in order to make the electromagnet de-magnetize immediately after power failure, we often use soft iron or silicon steel material to make the demagnetization faster. Such an electromagnet is magnetic when energized, and the magnetism disappears after power failure. Electromagnet in our daily life has a very wide range of sets of use, because of its invention also makes the generator power has been greatly improved. Principle: When an iron core is inserted into an energized solenoid, the iron core is magnetized by the magnetic field of the energized solenoid. The magnetized iron core also becomes a magnet, so that the magnetism of the solenoid is greatly enhanced due to the superposition of the two magnetic fields. In order to make the magnetism of the solenoid stronger, usually made of iron core hoof-shaped. But pay attention to the hoof-shaped iron core coil winding to the opposite direction, one side clockwise, the other side must be counterclockwise. If the winding to the same, the two coils of the core magnetization will cancel each other out, so that the core does not show magnetic. In addition, the core of the electromagnet is made of soft iron, not steel. Otherwise, once the steel is magnetized, will maintain long-term magnetism and can not demagnetize, the strength of its magnetic can not be controlled by the size of the current, and the loss of electromagnet should have the advantage. Electromagnet Electromagnet is a device that can generate magnetic force by passing current, which is a non-permanent magnet, and it can be easily activated or eliminated by its magnetism. For example, large cranes use electromagnets to lift abandoned vehicles. When an electric current is passed through a wire, a magnetic field is created around the wire. Applying this property, when current is passed through a solenoid, a uniform magnetic field is created within the solenoid. Assuming that a ferromagnetic material is placed in the center of the solenoid, the ferromagnetic material will be magnetized and the magnetic field will be greatly enhanced. Generally speaking, the magnetic field produced by an electromagnet is related to the size of the current, the number of coils and the ferromagnet in the center. When designing an electromagnet, attention will be paid to the distribution of coils and the selection of ferromagnets, and the current level will be used to control the magnetic field. Since the material of the coils has resistance, this limits the size of the magnetic field that an electromagnet can produce, but with the discovery and application of superconductors, there will be an opportunity to go beyond the existing limitations. Classification According to the current 1.AC electromagnet 2.DC electromagnet According to the use 1.Brake electromagnet: used as the mechanical brake of the motor in the electrical transmission device, in order to achieve the purpose of accurate and rapid stopping, the common models are MZD1 (single-phase), MZS1 (three-phase) series. 2. Lifting solenoid: used as lifting device to lift steel, iron sand and other magnetic materials, or used as electromagnetic manipulator to clamp steel and other magnetic materials. 3. Valve solenoid: using magnetic force to push the magnetic valve, so as to achieve the purpose of valve opening, closing or reversing. 4. Traction solenoid: mainly used to traction mechanical devices to perform automatic control tasks. Direction judgment solenoid magnetic field direction can be used to determine the Ampere's rule. Ampere's rule is the current and the current excitation magnetic field of the relationship between the direction of the magnetic inductance of the rule, also known as the right-hand spiral rule. (1) Ampere's rule in an energized wire (Ampere's rule I): Hold an energized wire in your right hand, with your thumb pointing in the direction of the current and your fourth finger pointing in the direction of the magnetic lines of force around the wire. (2) Ampere's rule in an energized solenoid (Ampere's rule II): hold the energized solenoid in your right hand and bend the four fingers in the same direction as the current, so that the end pointed to by your thumb is the N pole of the energized solenoid. Advantages Electromagnet has many advantages: the magnetism of the electromagnet can be used to control the on and off current; the size of the magnetism can be used to control the strength of the current or the number of turns of the coil; can also be changed by changing the resistance to control the size of the current to control the size of the magnetism; its magnetic poles can be changed by the direction of the current to control, and so on. That is: the strength of the magnetism can be changed, the presence or absence of magnetism can be controlled, the direction of the magnetic pole can be changed, the magnetism can be due to the disappearance of the current and disappear. Electromagnet is the current magnetic effect (electric magnetism) of a set, and life is closely linked, such as electromagnetic relays, electromagnetic cranes, magnetic levitation trains, electronic door locks, intelligent channel ramp, electromagnetic flow meter, and so on. Classification Electromagnets can be divided into two main types: DC magnets and AC electromagnets. If the use of electromagnets, can be divided into the following five: (1) traction electromagnet - mainly used to traction mechanical devices, open or close various valves to perform automatic control tasks. (2) lifting electromagnet - used as lifting devices to lift ingots, steel, iron sand and other ferromagnetic materials. (3) Brake solenoid - mainly used for braking the motor to achieve the purpose of accurate parking. (4) Electromagnetic system of automatic electrical appliances - such as electromagnetic relays and contactor electromagnetic system, automatic switch electromagnetic release and operation electromagnet. (5) Other uses of electromagnets - such as electromagnetic suction cups for grinding machines and electromagnetic vibrators. History As early as the spring of 1820, Denmark's Auster discovered this principle in a chance. 1822, the French physicists Arago and Lussac found that when the current through which there is a piece of iron in the winding, it can make the winding in the iron magnetization. In 1823, Sturgeon also did a similar experiment: he is not a magnet on a U-shaped iron bar around 18 turns of bare copper wire, when the copper wire and voltaic batteries connected to the copper coils around the U-shaped iron bar on the copper coils that produce a dense magnetic field, which makes the U-shaped iron bar into a "electromagnet ". This electromagnet on the magnetic energy than the permanent magnet can amplify many times, it can suck up than it is 20 times heavier than the iron, and when the power supply is cut off, the U-shaped iron bar on what iron can not be sucked, and become an ordinary iron bar. Sturgeon's invention of electromagnet, so that people see the bright prospects for the conversion of electrical energy into magnetic energy, this invention soon spread in the United Kingdom, the United States and some coastal countries in Western Europe. In 1829, the American electrologist Henry Sturgeon electromagnet device for some innovation, with magneto-electric insulated wire instead of bare copper wire, so do not have to worry about being too close to the copper wire and short circuit. Because the wires have an insulating layer, they can be tightly wound together in a circle, because the denser the coil, the stronger the magnetic field generated, which greatly improves the ability to convert electrical energy into magnetic energy. By 1831, Henry had tried out a newer electromagnet, which, although it was not very large, was able to suck up a 1-ton block of iron. In the Auster current magnetic effect experiments and a series of other experiments under the inspiration , Ampere recognized that the essence of the magnetic phenomenon is the current, involving the current, the magnet's various interactions are attributed to the interaction between the current, put forward to find the basic problem of the law of interaction of the current element. In order to overcome the difficulty that isolated current elements cannot be directly measured, Ampere carefully designed four show-zero experiments and accompanied by careful theoretical analysis, and came up with the results. However, due to the electromagnetic action of Ampere held the concept of super-distance action, had imposed in the theoretical analysis of the assumption that the force between the two current elements along the connecting line, expect to comply with Newton's third law, so that the conclusion is wrong. The above formula is the result of the correction by discarding the erroneous assumption that the force is along the line. It should be understood in terms of the proximity view of action as the current element generates a magnetic field, which exerts a force on another current element in it. Properties The Ampere's rule for a straight line current also applies to a small section of straight line current. A ring current can be viewed as a number of small segments of linear current, and for each segment the Ampere's rule for linear currents is used to determine the direction of the magnetic susceptibility along the central axis of the ring current. Superimposed on the center axis of the ring current to get the direction of the magnetic induction. Linear current Ampere's law is the basic, ring current Ampere's law can be derived from the linear current Ampere's law linear current Ampere's law of magnetic field generated by linear motion of charges also applies, when the direction of the current is the same as the direction of motion of the positive charges, and the direction of motion of the negative charges in the opposite direction. Significance Ampere's law is comparable to Coulomb's law, the basic experimental law of magnetic interaction , which determines the nature of the magnetic field and provides a means of calculating the interaction of electric currents. NOTE Electromagnet: A device that uses the magnetic effect of an electric current to make a soft iron (the internal mandrel of an electromagnet coil, which can be quickly magnetized and demagnetized) magnetic. WEISTRON ELECTROMAGNET (1) A soft iron bar is inserted into a solenoidal coil, and when the coil is energized with current, 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, coupled with the original magnetic field inside the coil, making the total magnetic field strength greatly enhanced, so the magnetic force of the electromagnet is greater than that of a natural magnet. (3) The greater the current of the solenoid coil, the greater the number of coils, the stronger the magnetic field of the electromagnet. Electromagnet sets (1) crane: for industrial use of strong electromagnet, through the large current, can be used to lift steel plates, containers, scrap iron, etc.. (2) telephone: the next section. (3) Ampere meter, volt meter, current meter (4) electric bell, etc.. (5) Automation control equipment (6) Industrial automation control, office automation. (7) Packaging machinery, medical equipment, food machinery, textile machinery, etc. (8) electromagnetic relay (9) maglev train production principle 1. Circular coil to the current formed by the magnetic field (1) the center of the coil in the direction of the magnetic field can be a small section of the coil on the wire as a straight line, by the right-hand rule of amperage to determine it. (2) the current on the circular coil of each small section of the current produced by the magnetic field, on the line in the circle are pointing in the same direction, so the magnetic field inside the coil than the straight wire current produced by the magnetic field strength. (3) When a circular wire is fed with current, the magnetic field outside the coil is not in the same direction as that produced by each small section of current, so the synthetic magnetic field produced is weaker than that inside the coil. (4) The higher the current and the smaller the radius of a circular coil, the stronger the magnetic field at the center of the coil. (5) The shape of the magnetic lines of force in a circular coil and a thin disk magnet are similar. 2. solenoidal coil current magnetic field (1) with a long wire wound into a solenoidal coil, equivalent to a number of circular coils connected in series, each circular wire in the center of the magnetic field are established in the same direction, you can enhance the effect of the center of the coil, the coil at the center of the magnetic field than a single turn of the circular coil for the strong. (2) Inside the coil, the magnetic lines of force form a straight line with the same direction, while at the ends of the coil, the magnetic lines of force are curved outward. (3) The properties of the magnetic lines of force in a solenoidal coil are similar to those of a bar magnet, and the magnetic lines of force inside the coil are in the opposite direction to those outside the coil. (4) The strength of the magnetic field inside the coil is directly proportional to the current in the coil and the number of turns of the coil per unit length. 3. The right-hand spiral rule (Ampere's theorem) for the direction of the magnetic field inside the current of a solenoid coil: hold the coil in your right hand, point the four fingers in the direction of the current, and the direction pointed by your thumb is the direction of the magnetic lines of force inside the coil. Loss of magnetism generator is not used for a long time, resulting in the loss of residual magnetism contained in the iron core before leaving the factory, the excitation coil can not establish a proper magnetic field, then the engine runs normally, but can not send electricity, this kind of phenomenon of the new machine. This phenomenon of new machines. Or long-term unused units are more. Treatment: 1) with excitation button, press the excitation button, 2) no excitation button, with the battery to its magnetization, 3) with a light bulb load, over speed running for a few seconds. Source of magnetic energy Low axial resistance generator in the principle of design, although only about 50% of the negative torque magnetic energy into positive torque magnetic energy, but the resulting positive torque 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). Through further research and analysis of the structure and working principle of conventional generators, we finally found a breakthrough, both in the construction of conventional power generation principles based on the use of "energy caching transfer method" to achieve the above purpose; that is, part of the fixed direction of the induction current for temporary processing, and then released in the lag time, the released energy can not only continue to output the supply of magnetic energy, but also the positive torque 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). The released energy can not only continue to output to supply the load, and the additional magnetic energy generated in the armature continuous current winding can also do positive work on the rotor (generate positive torque). This is the source of the positive torque energy of a low axial resistance generator. DEMAGNETIZATION HAZARD A generator demagnetization fault is a sudden total or partial loss of generator excitation. The causes of demagnetization are: rotor winding failure, exciter failure, automatic demagnetization switch tripped, semiconductor excitation system in some components are damaged or circuit failure, and misoperation and so on. Due to asynchronous operation, the rotor mechanical speed of the generator is greater than the synchronous speed, and due to the rotational difference, the stator winding current increases, and the rotor winding produces induced current, which causes additional heating of the stator and rotor windings. Analysis shows that the generator demagnetization of the power system and the generator itself will cause varying degrees of harm, summarized in the following aspects. Hazards to the generator itself: (1) generator demagnetization, the stator end of the magnetic leakage enhancement, so that the end of the components and end of the core overheating. (2) After asynchronous operation, the equivalent reactance of the generator decreases from . As a result, the reactive power absorbed from the system increases, overheating the stator winding. (3) The differential frequency current in the rotor winding of the generator produces additional losses in the rotor winding, causing the rotor winding to heat up. (4) For large direct-cooled turbine generators, the maximum value of the average asynchronous torque is smaller, the inertia constant is relatively lower, and the rotor is significantly asymmetrical in terms of the longitudinal and transverse axes. For these reasons, the torque and active power of a demagnetized generator under heavy load will oscillate violently. This effect is more serious for hydro generators. Hazards to the power system: (1) After the generator is demagnetized, due to the active power swing and the reduction of the system voltage, it may lead to the loss of synchronization between the adjacent normally operating generators and the system, causing system oscillation. (2) Generator demagnetization causes a large amount of reactive power in the system to be missing, and when the reactive power reserve in the system is insufficient, it will cause voltage drop. In serious cases, it will cause voltage collapse and system disintegration. (3) A generator demagnetization causes voltage drop, and other generators in the system will increase their reactive power output under the action of automatic regulation excitation device. Thus, some generators, transformers, transmission lines overcurrent, backup protection may be due to overcurrent action, expanding the scope of the fault. Comparison with permanent magnets Both permanent magnets and electromagnets can be manufactured to produce different forms of magnetic fields. When selecting a magnetic circuit, the first consideration is the job you need the magnet to do. Permanent magnets are advantageous in situations where electricity is inconvenient, power outages occur frequently, or where there is no need to adjust the magnetic force. Electromagnets are beneficial for uses that require a change in magnetic force or require remote control. Magnets should only be used in the manner for which they were originally intended, and applying the wrong type of magnet to a particular application can be extremely dangerous or even fatal. Many machining operations are performed on heavy, blocky materials, and these applications require permanent magnets. Many machine shop users feel that the greatest advantage of these magnets is that they do not require electrical wiring. Permanent magnets feature lift capacities of 330 to 10,000 pounds, and the magnetic circuit can be turned on or off with the turn of a handle. Magnets are typically equipped with a safety lock to ensure that the magnet does not accidentally disconnect while lifting. Magnet sets can be used for longer loads that are heavier and cannot be handled by a single magnet. Also, in many cases the parts to be prepared for machining are very fine (0.25 inches or finer) and have to be extracted from a pile of similar parts. Permanent magnets are not suited for jobs where you are lifting one piece at a time from a pile of parts. Permanent magnets, while extremely reliable when used correctly, cannot change the magnitude of the magnetic force. In this regard, electromagnets enable the operator to control the strength of the magnetic field by means of a variable voltage control device and are capable of picking out one piece from a stack of parts. Self-contained electromagnets are the most cost-effective magnets in terms of lifting capacity per unit, which can extend to 10,500 pounds. Battery-powered magnets are useful in that they utilize self-contained gel batteries to increase lift capacity and can handle flat, round, and component shapes. Battery-powered magnets are capable of repeating the lifting action, providing considerable lifting capacity without an external power source.