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Causes of Diesel Generator Brushes and Slip Rings Failure

Jan. 22, 2022

For the causes and solutions of common faults of diesel generator brushes and collector rings, the most common faults of diesel generator brushes in operation are heat generation, spark generation, and serious burning of brush holders and collector rings. From the perspective of the causes of overheating failures, there are mainly the following aspects:


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Heat caused by poor ventilation: The poor ventilation of diesel generators is mainly due to the blockage of cooling air ducts, the blockage of ventilation ditch and ventilation holes on the surface of the collector ring, and the decrease of air volume of the circulating fan, especially when the surface temperature of the collector ring is too high during operation. , it will lead to increased wear of the brushes and increased accumulation of carbon powder, which may block the heat dissipation channel on the surface of the collector ring. Therefore, when overhauling, the ventilation grooves, holes and cooling air duct filters on the surface of the collector ring should be cleaned to keep them unobstructed. For the collector ring that has been turned for many times, if the height of the ventilation groove on the surface of the collector ring is less than 5mm, and the radial limit hole has been turned, it should be replaced according to the minimum operating outer diameter according to the instructions to ensure the integrity of the collector ring. Mechanical and thermal reliability.


Heat generation due to excessive contact resistance or uneven distribution: Diesel generator collector rings and brushes conduct excitation current through mutual sliding contact. According to different capacities and models, there are approximately Dozens of brushes, due to the difference in contact resistance and current distribution, will cause uneven heating. There are several reasons for the following reasons:


(1) The contact resistance between the brush and the surface of the slip ring, the contact resistance between the brush and the brush, the brush The contact resistance between the braid and the brush holder lead is too large. It can be checked by measuring the total voltage drop of a single brush, the contact pressure drop of the brush, the pressure drop of the brush body, the pressure drop of the connection, and the pressure drop of the brush braid. At the same time, check whether the screws in the circuit are tightened. Check the cleanliness of the brush contact surface and whether there is oil pollution.


(2) The pressure of the brush is uneven or does not meet the requirements. There may be reasons such as the short brush and the loss of elasticity of the spring due to overheating, softening and aging. Brush pressure should be checked with a spring balance. The constant pressure spring should be complete without mechanical damage, the pressure should meet the requirements of its products, and the spring pressure deviation on the same pole should not exceed 5%; for non-constant pressure brush springs, the pressure should meet the requirements of its products when there are regulations. When specified, it should be adjusted to the minimum pressure that does not make the brushes catch fire, generally 140-250g/cm2, and the pressure of each brush on the same brush holder should be uniform.


(3) The contact resistance between the collector ring and the rotor lead is too large. In this case, the fastening screws between the collector ring and the rotor lead should be reinforced.


(4) The brush material is poor, the electrical conductivity is poor, the model used does not meet the requirements, or different types of brushes are used. The brushes of the same type and the same manufacturer should be used on the same motor, and the brushes with obvious differences in appearance inspection should be replaced.

 

Overheating due to mechanical and frictional reasons: a large part of the overheating faults of the collector rings and brushes of diesel generators are due to overheating caused by mechanical and frictional reasons. The temperature of the electric ring and the brushes is high, or the temperature is too high during operation. After pulling out a few brushes, the temperature decreases, which is basically due to mechanical and frictional reasons. The situation of heating caused by machinery and friction is very complicated, mainly in the following aspects:


(1) The contact surface of the brush is poorly ground or too many brushes are replaced at one time during operation. Replace the brushes during operation. At the same time, only 1-2 brushes are allowed to be replaced on each brush holder. The replaced new brushes should be ground on a model with the same diameter as the collector ring in advance, and the old and new grades must be the same. If there are many brushes to be replaced at one time during overhaul, sufficient time should be left for the oxide film to form on the surface of the brushes when rushing before putting into operation.


(2) The contact surface between the brush and the collector ring is too small, and the contact area should generally not be less than 75% of the cross section of a single brush.


(3) The brush swings in the brush box or the action is jammed. The brush should be able to move up and down freely in the brush holder, and the gap should meet the product regulations. When there is no regulation, the gap can be 0.10-0.20mm. The shape of the brush should be square, and the size error of the upper and lower ends should not be greater than 0.05mm.


(4) The gap between the brush holder and the surface of the collector ring is too large. Due to the brittle material of the brush, when the gap between the brush holder and the surface of the collector ring is too large, the brush cannot contact the collector ring as a whole during operation, and the contact with the collector ring is inclined, which is easy to cause the brush to crack. The gap between the brush holder and the surface of the collector ring should meet the technical requirements of the product. When the product is not specified, the gap can be adjusted to 2-3mm. When adjusting the gap, a layer of 2-3mm thick rubber pad can be used to attach the collector ring. surface, place the brush holder against the rubber pad, then tighten the set screw to remove the rubber pad.


Starlight Power was founded in 1974 and is one of the earliest manufacturers of generators and diesel generator sets in China. If you want get more information, please feel free to send email to sales@dieselgeneratortech.com we will pay highly attention on your question.

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