Factors causing carbon brush heating: 1. Increased dispersion of carbon brush resistance leads to increased resistance heating of the carbon brush. 2. Carbon brush jamming. After the carbon brush is powered on, the brush body expands and easily gets stuck in the brush holder; Due to vibration, non perpendicular brush grip, and other reasons, some carbon brushes may experience significant jamming on the upper edge of one side of the brush grip and the lower edge of the other side. These forms of jamming can still be measured with a caliper, which can be easily misled. At this point, the carbon brush has failed, causing an increase in the current allocated to other carbon brushes and an increase in heat generation. 3. The carbon brush pressure decreases. Although it is a constant pressure brush grip, there are differences in the pressure of each spring. When the pressure is low to a certain extent, the contact is unstable, the contact pressure drop increases, and the heat generation significantly increases. At the same time, due to insufficient spring pressure, the elongated contact surface between the brush holder and the carbon brush increases the frictional resistance on the side of the carbon brush, causing the carbon brush to be trapped inside the holder. 4. A gas film is formed on the contact surface of the carbon brush. When the carbon brush operates at the maximum allowable speed, it is easy to produce gas film and jumping on the contact surface, and the current flowing through the carbon brush is unstable. Cutting grooves and grinding on the surface of the slip ring can cause damage to the gas film on the contact surface of the flower carbon brush. But opening grooves reduces the actual contact area of the carbon brush. 5. The formation of slip ring oxide film: If the slip ring oxide film is too thick, the contact resistance of the carbon brush increases, and the excitation current is diverted to other carbon brushes with lower circuit resistance. 6. Disruption of current balance. In general, the contact tension between the carbon brush and the slip ring is high, the contact voltage drop is small, all carbon brushes have similar working conditions, the current of each carbon brush is close to equal, the average temperature of the brush body is low, and the current between the carbon brushes is relatively stable and balanced. After running for a period of time, factors such as oxide film, gas film, and long resistance appear. The carbon brush is worn short or the spring pressure decreases. The contact force of the carbon brush contact surface decreases, and the current between the carbon brushes is redistributed. The current difference between each carbon brush increases and is in an unstable equilibrium. This stage takes a long time, gradually changes, and is not easy to detect. When the ambient temperature rises or the excitation current increases, it can cause balance disruption at any time.
When the heating is in its initial stage and the heating temperature is not higher than 100 ° C, the method of adjusting some poorly functioning carbon brushes can be used. Replace worn carbon brushes with low working current; Adjust or replace some brush grip springs with lower elasticity to optimize current distribution. 2. Reduce the reactive load of the generator appropriately, decrease the excitation current, lower the working current of the carbon brush, and alleviate heat generation. 3. When individual carbon brushes break their braids, the excitation current can be reduced first; When the ring fire occurs, greatly reduce the excitation current, adjust the carbon brush current balance before replacing the carbon brush, and do not forcefully replace a large number of carbon brushes. 4. Clean the ventilation opening and keep the air duct unobstructed.
Emergency treatment for heating: When the temperature reaches 120 ° C or above, replacing the carbon brush or adjusting the brush holder cannot reduce the overall temperature. Due to the small and uneven contact area between the newly replaced carbon brush and the slip ring, regardless of the current distribution, heat conduction will cause the temperature to rise. The most important measure at this time is to lower the working temperature and improve the working conditions of the carbon brush and brush holder. 1. The method of removing the faulty carbon brush during normal operation, if the working current and ambient temperature do not change significantly, but the carbon brush temperature increases significantly, may be caused by a small number of carbon brush faults (such as increased resistance, decreased spring pressure, long and rough carbon brushes, broken carbon brushes, etc.). At this point, it is necessary to accurately identify the carbon brush that caused the heating and remove it, so that other carbon brushes can work normally and enter a normal equilibrium state. The key to this approach is to make accurate judgments. Faulty carbon brushes generally exhibit vibration, high current, and sometimes their temperature is higher than the overall temperature. If accurate judgment cannot be made, experimental methods can be used to take out a brush grip at regular intervals until the overall temperature shows a significant decrease. After the system temperature returns to normal, reinstall the processed carbon brush.
