(1) Pure mechanical wear: The surfaces of the carbon brush and the slip ring are in contact. Due to spring pressure and elastic deformation of the material, parts in direct contact are embedded in each other. When sliding relative to each other, there will of course be friction and wear. If the particles of the carbon brush are fine and soft, the carbon powder will easily stick to the surface of the slip ring, making the slip ring have a shiny and smooth mirror surface. The grinding surface of the carbon brush will also be very. smooth and the mechanical wear of both will be low. However, if the quality of the carbon brush is poor, if the particles are coarse and hard, or even contain some hard particles like emery, the surface of the slip ring will inevitably be scratched, causing the slip ring to appear chipped or damaged. metallic texture. , and the tank broomgood itself will be ground. There will also be lines drawn after the hard particles fall, which significantly increases mechanical wear.
(2) Electrical wear and mechanical wear under the action of electric current, there is not only mechanical wear, but also electrical wear. So-called electrical wear refers to damage to the pole surface material due to factors such as high arc temperature and discharge. Since electrical wear affects the surface of the poles, it will also impact the degree of mechanical wear. Because the current passes through the contact surface of the carbon brush and the slip ring, and the direct conduction parts are constantly changing, the current density is very large, making some points very hot and due to the temperature high arc, the polar surfaces on both sides will partially melt. If it falls, the metal will turn into vametal fear and the carbon brush structure will loosen and fall due to oxidation and corrosion. This is a manifestation of electrical wear. However, the wearing conditions are different depending on the polarity. Under the action of the arc, the surface of the anode (positive electrode) heats up locally and evaporates "metal vapor", causing corrosion of the anode surface. This is called “anode evaporation”; emits electrons due to the impact of positive ions and high temperature, causing the cathode. The surface is also damaged, which is called “sputtering”. Due to the effects of anode evaporation and cathode powdering, carbon brushes and slip rings will exhibit polarity differences due to different current directions.
When current flows from the carbon brush to the slip ring, the carbon brush is the electrpositive ode and the slip ring is the negative electrode. The result is: A slight degree of anode evaporation occurs on the carbon. surface of the brushes, and the carbon particles and graphite ions migrate to the surface of the slip ring, the carbon brushes exhibit electrical wear. There is light cathode powder on the surface of the slip ring, and carbon particles and graphite are attached to it, forming a smooth and shiny mirror surface. Thanks to the smooth surface of the slip ring, mechanical wear is reduced. When current flows from the slip ring to the carbon brush, the carbon brush is the negative electrode and the slip ring is the positive electrode. The result is: cathodic powdering occurs on the surface of the carbon brush, and the electrical wear is small. Anodic evaporation occurs on the surface of the slip ring. A large amount of metal evaporatese, causing serious damage to the surface. At the same time, these metal particles are also easy to attach to the worn surface of the carbon brush, which will cause significant wear and streaking on the surface of the commutator. In this case, the surface of the slip ring is rough and metallic, and the mechanical wear between the surfaces is significant.
In general, when the carbon brush is the positive electrode: the electrical wear of the carbon brush is large, the mechanical wear is light, and the electrical wear and mechanical wear of the slip ring are both weak; when the carbon brush is the negative electrode, the carbon brush The electrical wear is small and the mechanical wear is large. Both electrical wear and mechanical wear of the slip ring are significant. In order to make the wear of the slip ring uniform, since the positive ring current flows from the carbon brush vers the slip ring, the carbon brush has positive polarity and the slip ring has negative polarity.Therefore, the wear of the positive ring is small; Likewise, wear on the negative ring is significant, so the polarity of the two rings must be swapped frequently. This is why power plants often swap the positive and negative ring connection cables during overhauls.
When there is no power, the coarse and hard particles on the grinding surface of the carbon brush are easily embedded in the surface of the slip ring, causing greater mechanical wear and even friction vibrations. When the current flows, the coarse and hard particles on the grinding surface of the carbon brush explode, pulverize and stick to the surface, thereby reducing friction, reducing mechanical wear and allowing the carbon brush to operate very quietly. Therefore, under normal current conditions, current is also beneficial in reducing mechanical wear. However, if the current density is too high, the anode will seriously evaporate, worsening electrical wear. When the electrical wear increases, the surface of the slip ring becomes rough, the metal powder adheres to the surface of the carbon brush, and the mechanical loss increases. Therefore, the current density through the carbon brush must have a limit. As for spring pressure, it also has an impact on wear. If the pressure is too low, the contact surface between the carbon brush and the slip ring will be unstable, easily causing arcing and increasing electrical wear. If the pressure is too high, the hard particles on the brush surface will seriously scratch the surface of the slip ring, which will also increase mechanical wear. The spring pressure must therefore bebe moderate. Master upstairs, please read the "circuit breaker" post carefully: You and I made the same mistake: the positive pole is very worn by the carbon brush, and the negative pole is very worn by the slip ring. Some generators from our company only. have insulation overheating detection devices. Its sensitivity and authenticity are very questionable, and it is basically not used as a reference for operation. Our factory is a hydrogen cooling unit. Its principle is to detect electrical ions in hydrogen to judge the quality of the insulation. the generator. The flow rate of the hydrogen sample has its value. It has a big impact and is basically waste. Your plant is probably a very old unit, so the insulation isn't even very good. -protection against bends. Dongfang Factory said the insulation is very good and no design is needede