Relay electromagnetic suction and suction characteristics

Everyone may have used electromagnetic appliances or other electromagnets in production practice. For comrades who often use these electrical components, they will definitely have such experience: when the voltage applied to the coil is constant, the farther the armature is from the core column, that is, the larger the air gap, the smaller the force it receives, The smaller the air gap, the greater the suction: if you want to increase the suction at a certain air gap, you must increase the voltage across the coil (if allowed). This experience shows that on the one hand, the electromagnetic attraction force decreases with the increase of the air gap (when the voltage is constant), and on the other hand, it increases with the increase of the coil voltage (when the air gap is constant). This fact, we can also use experiments to prove. For example, for the electromagnetic system shown in Figure 2-11a, the suction characteristics measured in the field are in the shape of a curve shown in Figure 2-11b. It further shows that the electromagnetic suction force not only increases with the decrease of the air gap, but also the suction force increases faster when the air gap is smaller, that is, the suction force characteristic curve becomes steeper. These are our perceptual knowledge of the characteristics of suction.

However, "what we feel, we can't immediately understand it, and only what we understand can we feel it more deeply." To understand why the suction characteristics have such characteristics and laws, and how to estimate them quantitatively, we must also The transformation process of electricity, magnetism and force in the electromagnetic system and its inner connection are further analyzed and discussed. Electricity is transformed into magnetism, and magnetism is transformed into force, which are two different transformations that take place simultaneously in an electromagnetic system. Electricity is converted into magnetism, that is to say, the energized coil will generate a magnetic phenomenon in the closed path of the core column, yoke, armature and air gap, making them magnetized and magnetic. This path is called the "magnetic circuit". In order to express the existence of magnetism in the magnetic circuit conveniently and vividly, it is usually represented by drawing a closed curve along the center line of the magnetic circuit, which is called "magnetic flux line". "Magnetic flux" is a physical quantity used in physics to measure the strength of magnetism. It is usually represented by the symbol Φ, and the unit is Maxwell or horse for short. The number of magnetic flux lines can reflect the strength of magnetism everywhere. Obviously, the strength of magnetism, or the size of the magnetic flux, is related to the parameters of the electric wire circumference. It is not difficult to understand that the greater the current (I) of the coil, or the more turns (W) of the coil, the greater the magnetic flux Φ it produces. Experiments have shown that the size of the magnetic flux is determined by the product of the coil current and the number of turns - I·W. This product is called "magnetic potential, symbol IW, and unit is ampere-turn. Magnetic flux exists in the magnetic circuit, so its magnitude is not only related to the magnetic potential that produces it, but also to the magnetic conductor in the magnetic circuit (ie. Ferromagnetic material) is related to the characteristic parameters of the air gap. The physical quantity used to describe the magnetic properties of the magnetic conductor, the air gap (that is, the air) is called "magnetoresistance", with the symbol R. The magnetic potential passes through the magnetoresistance in the A magnetic flux is established in the magnetic circuit, which is the process of converting electricity into magnetism, and experiments have also proved that there is an inherent and definite conversion law between the three. Therefore, it is also called Ohm's law in the magnetic circuit. There are With it, we can estimate the quantitative relationship between the magnetic potential and the magnetic flux when the magnetic circuit is fixed. The magnetism is converted into a force. This conversion process also has its inherent definite regularity and quantitative relationship.

By the way, the magnetic flux generated by the coil current exists not only in the magnetic conductor, but also in the surrounding space of the magnetic circuit, so the former is called the main magnetic flux and the latter is the leakage magnetic flux. Obviously, the existence of the leakage flux will affect the size of the suction force and the shape of the suction force characteristics. We will not go into detail about these.