Factors causing heating of carbon brushes: 1. The dispersion of resistance of carbon brushes increases, which increases the heating resistance of carbon brushes. 2. Carbon brush jam. After the carbon brush is turned on, the brush body expands and easily gets stuck in the brush holder; some carbon brushes will have obvious jamming on the upper edge of one side of the brush holder and the lower edge of the other side due to vibration, non-vertical brush holder, etc. These types of resistors can still measure current with a clamp meter, but they can easily be misled. At that time, the carbon brush failed, causing the current distributed by the other carbon brushes to increase and heat generation to increase. 3. Carbon brush pressure decreases. Although it is a constant pressure brush handle, the pressure of each respell is different. When the pressure is low enough, the contact becomes unstable, the contact pressure drop increases, and heat generation increases significantly. At the same time, due to insufficient spring pressure, the contact surface between the brush holder and the carbon brush is lengthened, which increases the friction resistance on the carbon brush side, and the carbon brush coal is stuck in the support. 4. A film of air forms on the contact surface of the carbon brush. When the carbon brush operates at the maximum allowable speed, it is easy to produce an air film and jump on the contact surface, and the current flowing through the carbon brush is unstable. The grooves and grinding on the surface of the slip ring are larger, and the contact surface of the carbon brush can destroy the air film. However, the grooves reduce the actual contact area of the carbon brush.5. Formation of the oxide film of the slip ring. The oxide film of the slip ring is too thick, the contact resistance of the carbon brushes increases, and the excitation current is shunted to other carbon brushes with low circuit resistance. 6. Destruction of the current balance. Under normal circumstances, the contact tightness between the carbon brush and the slip ring is large, the contact pressure drop is small, the working conditions of all carbon brushes are similar, the current of each brush carbon is close to the same, the average temperature of the brush body is low, and the current between the carbon brushes is relatively stable and balanced. After a certain period of operation, factors such as oxide film, air film, long resistance, etc. will occur. appear, the carbon brushes are worn short or the spring pressure is reduced, the contact tightness of the surface ofcontact of the carbon brushes is reduced, the current between the carbon brushes is redistributed, and the current of each carbon brush The difference increases and is in unstable equilibrium. This stage takes time, evolves gradually and is not easy to detect. When the ambient temperature increases or the excitation current increases, damage to the balance may occur at any time.
Heat treatment 1. When the heating is in the initial stage and the heating temperature is not higher than 100°C, you can adjust some carbon brushes which do not work well. For example, replace worn carbon brushes with low operating current; Adjust or replace some of the less elastic brush holder springs to optimize current distribution. 2. Appropriately reduce the reactive load of the generator, reduce the excitation current, reduce the operating current of thecarbon brush and reduce heat generation. 3. When individual carbon brushes are broken, the excitation current can be reduced first; when there is a ring fire, the excitation current can be greatly reduced, and the carbon brushes can be replaced after adjusting the current balance of the carbon brushes. do not forcibly replace a large number of carbon brushes. 4. Clean air vents and keep air ducts clear.
Emergency treatment for heating: When the temperature exceeds 120°C, replacing the carbon brush or adjusting the brush holder cannot reduce the overall temperature, because the new carbon brush has less contact area with the slip ring and is not fluid. No matter how much current it distributes, heat conduction will increase its temperature. The most important measure at present is to lower the travail and improve the working conditions of the carbon brush and brush holder. 1. How to remove defective carbon brushes. During normal operation, if the operating current and ambient temperature do not change much, but the carbon brush temperature rises significantly, it may be caused by a small number of carbon brush failures (such as resistance increased). , elasticity, etc.)The spring pressure is reduced, the carbon brush is long, the carbon brush is broken, etc.). At this time, the carbon brush causing the heat must be accurately identified and removed so that the other carbon brushes can operate normally and enter a normal equilibrium state. The key to this approach is making accurate judgments. Defective carbon brushes usually exhibit vibration, high current, and sometimes their temperature is higher than the overall temperature.If you cannot judge accurately, you can use the test method and remove a brush holder at regular intervals until the overall temperature drops significantly. Once the system temperature returns to normal, reinstall the treated carbon brushes.