Operation and maintenance of generator carbon brushes and slip rings

Operation and maintenance of generator carbon brushes and slip rings Zhang Wenyuan, Liu Huailiang (Sunshine Power Generation Co., Ltd., Yangquan 045200, Shanxi) and the operation of carbon brushes have raised high requirements, mainly for the slip ring of Unit 3 of Sunshine Power Generation Co., Ltd. Treatment, modification of carbon brush, modification of air duct and operation and protection of slip ring carbon brush, detailed description is given. Table 1 Fan ventilation cooling parameter design value No. 1 No. 2 machine Actual value machine actual value No. 3 machine The actual value of the actual value of the No. 4 machine, the wind power of the College of Power Systems and Automation, engineers; 1994 Liu Huaixin male a mountain S set people two gas fools special work - brewing oil carbon brush bad contact rightsreserved. 1 generator excitation system and carbon brush profile Sunshine Power Generation Co., Ltd. generator is a 2-20 type 300MW steam turbine generator produced by Dongfang Motor Factory. Its excitation system is AC exciter with permanent magnet exciter - static rectifier cabinet excitation system rated excitation voltage 463V rated excitation current The 2203A generator slip ring is made of alloy Forged Steel with good wear resistance. The surface car has spiral groove to improve the contact performance of the carbon brush. The radial ring of the slip ring has ventilation holes for cooling. Slip ring. The diameter of the slip ring is 455mm, and its peripheral speed is 71. /s generator carbon brush is 72 pieces, 36 pieces of positive and negative poles are arranged in 4 rows. The pressure is provided by the double tongue constant pressure spring. Now use the D172 type carbon brush. The specification is 60mm carbon brush and the cooling of the slip ring is cooled by the fan installed in 6.3m. The gas source is taken from 6.3m. The relevant parameters are shown in Table 1. 2 There is a problem in the operation of the generator carbon brush. The carbon brush is hot, especially in summer. The situation is even worse. The temperature rise of the carbon brush and the slip ring is higher than 120*C. In order to reduce the operating temperature, the blower must be used to enhance the uneven distribution of ventilation and cooling current. Some are greater than 200A, and some are only below 10A. The carbon brush is fired, and the brush is overheated and discolored; after adjustment, the normal operation can be maintained for a short time, and the current is uneven and the temperature rises after a long time (about 4 hours); and the wear of the generator slip ring is serious. Shorten the life of the slip ring.

The carbon brush is too tight in the brush grip, adapting to inflexibility, the brush grip and the compression spring are damaged and deformed during operation. The slip ring is eccentric, the brush grip is not fixed properly, causing the carbon brush to wear too much, and even bouncing, the unit is rushed when it is serious. In the process, the carbon brush can be broken by 3m, the inlet temperature is high, and the cooling effect on the carbon brush is poor. Sometimes the whole row of carbon brush is beating. Due to the above situation, the safe operation of the generator is seriously affected. 3rd generator carbon brush, brush holder, air duct transformation 3 reasons analysis of the current D172 carbon brush contact resistance range of variation, easy to cause a large difference in contact resistance between each carbon brush and slip ring, causing the current distribution of each carbon brush Uneven, high heat difference, large current, high temperature carbon brush after long-term operation, causing the oxide film on the contact surface of the carbon brush and the slip ring to damage the brush overheating (sometimes causing the brush to blow), causing the carbon brush to contact the slip ring The resistance is large, the pressure of the compression spring is lowered after the high temperature, and finally the carbon brush current is reduced; the result is that the other contacted carbon brushes are over-current, and finally burned, further causing the deterioration of the carbon brush operating condition, the slip ring High temperature wear and tear, severe ring fire, burnt slip ring, generator forced to stop D172 carbon brush bulk density, poor gas permeability, large modulus of elasticity, allowing small peripheral speed (70m / s) can not meet the peripheral speed of the generator Requirements, easy to create an air cushion between the carbon brush and the slip ring, resulting in the comparison of the performance of the table 2NCC634 and D172 carbon brush parameters imported NCC634 domestic D172 resistivity / magic * 155) O235 (rated 155) wire does not overheat color line overheating color duct resistance Large, poor rigor, small fan head, so that the carbon brush cooling air volume is insufficient (design air volume 3m3 / s); carbon brush cooling fan air inlet is taken from 6.3m, and 6.3m high ambient temperature, resulting in high cooling air source temperature Because the pressure spring directly contacts the carbon brush, due to heat conduction, the spring is fatigued at a higher temperature, the pressure is lowered, and the carbon brush is broken due to vibration during the fracture process of the compression spring. The main reason is due to the brush holder and the brush. The grip is not fixed properly, the carbon brush wears an oblique angle, the unit speed changes greatly, and the unit vibrates greatly at the critical speed. The tangential direction of the extension shaft produces a shear stress on the carbon brush, and the carbon brush is broken; When the carbon brush is reversed, the same reason may occur. The reason why the whole row of carbon brushes vibrate during operation is that the surface of the generator slip ring is deteriorated due to the operating conditions, the surface of the slip ring is unevenly worn, and the uneven edges are formed, and then the slip ring is formed. It is not a regular circle itself, causing the vibration of the carbon brush.

4 Generator carbon brush transformation situation During the shutdown of No. 3 machine, the generator-sliding ring was washed in the state of the car, and after the car washing, the slip ring was rubbed with the cotton wheel to round the slip ring. And guarantee the smoothness of the slip ring.

Through the comparison of carbon brush parameters, the NCC634 carbon brush with small contact velocity variation and high peripheral velocity (P71.435) with small bulk density and good gas permeability was selected. When replacing, all carbon brush shunts were measured once, then the minimum split flow was selected. The carbon brush is replaced, and after all the carbon brushes are shunted, after all the new carbon brushes are replaced, after the operation for a few days, the carbon brush shunt is measured, and the current deviation is obviously small (the current is about 70A). , the current is small about 30A), the carbon brush and the slip ring are in contact with the NCC634 and D172 carbon brush parameters. See Table 2 to modify the No. 3 generator carbon brush air duct. From the original 6. Take the gas to the gas from 0m. The inlet air temperature is lowered, and the cooling of the carbon brush is obviously improved. 5 The remaining problem is the use of a double-tongue compression spring. The carbon brush is inflexible in the upper and lower movements of the brush holder. The pressure is not damaged during the operation of the carbon brush center, and the aluminum brush holder is deformed. damage.

Because the brush grip is not correct, although the slip ring has been rounded and polished, the carbon brush is still stressed, and it is easy to vibrate and bounce.

Carbon brush cooling air volume still meets the requirements. In view of the above situation, it is planned to renovate the generator brush holder during the overhaul of Unit 2 and re-select the fan.

6 Operation and maintenance precautions When the unit starts, the carbon brush cooling fan is started before the unit is rushed to cool the heat generated by the friction between the carbon brush and the slip ring during the reversing process.

When the brush holder and the brush holder are disassembled, it is necessary to mark it and compare the gap between the running slip ring and the carbon brush to ensure that the brush holder and the brush holder are properly installed.

In the operation, the DC clamp current meter is used to measure the carbon brush shunt condition. When the deviation is large, the carbon brush pressure should be adjusted in time to carry out the upper and lower lifting activities of the carbon brush regularly to prevent the carbon powder from jamming the carbon brush and the brush grip.

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