To understand their function, you must first understand the basic principles of electrical energy and kinetic energy conversion, that is, you must understand the principle of motors.
The principle of power generation: After the magnetic field cuts the wire, an electric current is generated in the wire. Generators cut wires by rotating a magnetic field. The rotating magnetic field is the rotor and the cut wire is the stator.
For the rotor to generate a magnetic field, a magnetic current must be entered into the rotor coil. It is used to send the strong magnetic current generated by the exciter generator into the rotor coil.
Function:
To put it simply, since the rotor rotates, the excitation current is transmitted to the winding (excitation winding) of the rotor through the contact between the carbon brush and slip ring.
How to manage overheatingment of generator carbon brushes
The brushes are made from precious metal alloy materials. They are "II" shaped and have a symmetrical double contact with the conductive ring. Groove. Using the elastic pressure of the brush and the conduction ring, the grooves slide into contact to transmit signals and current.
Collection rings are also called conductor rings, slip rings, collector rings, bus rings, etc. It can be used in any electromechanical system requiring continuous rotation while transmitting power and signals from a fixed position to a rotating position. Slip rings can improve system performance, simplify the system structure, and prevent wires from being strained during rotation.
Synchronous motors with slip rings and asynchronous motors using slip rings are widely usedized in industrial sectors and most of them operate under various harsh conditions. Although these motors do not have the commutating function of DC motors, like commutators, they also suffer from abnormal wear of commutator rings or brushes, brush vibration, and spark generation. Especially from the perspective of brush material, not only graphite brushes are used for slip ring brushes, but also metal graphite brushes are sometimes used to increase the current density of the brush. Therefore, factors such as abnormal residual expansion must also be considered. Even for high-speed engines such as turbogenerators or engines operating in fully enclosed gas and hydrogen media, many problems arise.
The material of the collector ring requires mechanical strengthe high, a good conductor of electricity and resistance to corrosion. When it is in sliding contact with the brush, it must have wear resistance and stable sliding contact characteristics. Generally, steel slip rings have good wear resistance and high mechanical strength, so they are mainly used in synchronous motors where the slip ring wear difference is large due to polarity.
The factors that cause fires in the collector ring of the generator are:
1. The quality of carbon brushes is poor. Carbon brushes break easily if overheated. causes the carbon brushes to come into contact with the collector. An arc between the collector rings;
2. Hydrogen leaking from the generator sealing tile near the collector ring;
3. The collector ring cooling air inlet is blocked, causingant drafts. The quantity is reduced, which affects the cooling effect of the collector ring surface;
4. The generator seal oil is leaking and the carbon powder is not discharged. smoothly, and the mixture of oil, gas and carbon powder contaminates the collector ring chamber;
< p>5. Poor contact between the carbon brush and the commutator ring surface, overheating of the commutator ring surface and carbon brush assembly, etc. Among them, poor contact between the carbon brush and the commutator ring causes the commutator ring to catch fire. The main cause of burning accidents. Poor contact between the carbon brushes and the commutator ring causes local sparking, causing an increase in the temperature of the commutator ring, deterioration of carbon brush contact, and uneven distribution of excitation current between the brushes of coal, resulting inring light. Poor contact between the carbon brush and the commutator ring surface is usually difficult to detect, resulting in commutator ring fires that last for a relatively short time and are therefore difficult to treat in time.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 moment the carbon brush fellbroken down, causing an increase in the current distributed by the other carbon brushes and an increase in heat generation. 3. Carbon brush pressure decreases. Although it is a constant pressure brush handle, the pressure of each spring 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 throughrs the carbon brush is unstable. The grooving and grinding of the slip ring surface is 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 contact surface 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 currentement; 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 working current of the carbon 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 heat brusharbon has less contact area with the slip ring and is not smooth regardless of its distribution. Regardless of the amount of current, heat conduction will increase its temperature. The most important measure at present is to lower the working temperature and improve the working conditions of the carbon brush and brush holder. 1. Method for removing defective carbon brushes During normal operation, if the working current and ambient temperature do not change much, but the carbon brush temperature increases significantly, it may be caused by a small number of failures of carbon brushes (such as increased resistance, reduced spring pressure, carbon (the brush is long, the carbon brush is broken, etc.). At this point, the carbon brush causing the heat should be identified with precision and removed so that other carbon brushes can operate normally and enter anormal state of balance. 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.