发电机组碳刷易发故障原因 Reasons for the easy failure of carbon brushes in generator sets

发电机组导致碳刷故障的因素

　　电磁因素：无功或励磁电流调整时，碳刷的火花有明显变化。在励磁机换向时，碳刷与换向片接触不良，接触电阻过大；整流子或滑环的氧化膜薄厚不均匀，引起碳刷电流分布不平衡；或者负载突然变化，以及突发的短路导致换向片间的电压分布异常；机组过载和不平衡；碳刷选型不合理，碳刷间距不等；碳刷质量问题等等。

　　机械因素：换向器中心不正，转子不平衡；机组振动大；换向片间绝缘凸出或换向片凸出；碳刷接触面研磨不光滑，或换向器表面粗糙而造成接触不良；换向器表面不清洁；各个换向极下气隙不等；碳刷上弹簧压力不均匀或大小不适宜；碳刷在刷握里太松而发生跳动，或太紧了碳刷在刷握里卡住了等。机组运转速度降低或震动改善，火花将减少。

　　化学因素：柴油发电机组运行在有腐蚀性的气体中，或机组运行空间缺乏氧气，换向器与碳刷接触的表面上一层自然形成铜氧化物薄膜遭到破坏，本已形成的、近似线性电阻的换向不复存在，在接触面重新形成氧化膜的过程中换向器火花加剧。换向器（或滑环）被酸性气体或油脂腐蚀。碳刷及换向器被污染等。

发电机组碳刷的维护

　　A、运行检查：加强定期与不定期的设备巡回检查工作，正常情况下,工作人员每天必须对发电机碳刷进行两次检查（上午一次，下午一次），用红外测温仪测量集电环和碳刷的温度，夏季高峰负荷期间以及无功和电压波动较大时应缩短温度测量间隔，更换的新碳刷做重点检查。有条件的单位应定期用红外热像仪测量集电环和碳刷的温度。并做好巡回检查设备运行工况记录。

　　B、检修更换：对新购进的碳刷进行验收。测定碳刷的固有电阻值，测量碳刷引线接触电阻，阻值要符合制造厂和国家标准。严格把握更换碳刷工艺，同一台柴油发电机使用的碳刷必须一致，不可掺插使用。在更换碳刷前，细心研磨碳刷使其面面光滑，电刷在刷握内应有0.2 0.4毫米的间隙，在刷握内上下活动自如。刷握的下边缘和换向器工作表面之间的距离为2-3毫米，距离过小，会碰撞换向器表面，易受损、距离过大电刷跳动易产生火花。争取实现碳刷接触面大于碳刷截面的80％。勤更换，但多次更换碳刷不宜过多，一次更换碳刷的数量不得超过单极总数的10％，碳刷顶端低于刷握顶端3mm的碳刷应尽快更换，每次更换碳刷时必须使用同一型号的碳刷，但要注意节约和充分利用碳刷。更换后的碳刷必须用直流卡钳表测量碳刷分流情况，用红外测温仪进行温度测试，防止个别碳刷因过流而过热。对于滑环或整流子换向片凸起与凹陷等明显设备问题，要利用机组检修的机会进行紧固、车磨。加强检修质量和运行控制，避免由于检修质量不良或运行调整不当造成机组运行中，汽轮机油外泄，甩到集电环上，增大碳刷与集电环之间的接触电阻。刷架和刷握在机组大、小修时要慎重调整，回放和安装刷架时，角度和几何位置要保证在原状态，碳刷的滑入边和滑出边必须要与换向器平行。

　　C、日常维护：勤清扫、吹灰，保持碳刷及整流子滑环光面清洁，若遇大风天气，或过后必须及时清扫。勤调整弹簧压力，碳刷弹簧的压力要符合制造厂家的规定，使碳刷承受压力均匀。防止个别碳刷过热或产生火花、刷辫烧焦烧断现象的发生。碳刷运行中出现问题必须及时消缺，避免恶性循环，危及机组正常运行。同一台机组使用的碳刷必须一致，不可掺插使用。进行维护的工作人员，检查维护时要特别小心，发辫应放在帽内、扣紧袖口，不使衣服及擦拭材料被机器挂住。工作时站在绝缘垫上，不得同时接触两极或一极与接地部份，也不能两个人同时进行工作。在转动着的电机上调整、清扫碳刷及滑环时，须有实践经验的同志进行。

Factors causing carbon brush failure in generator sets

Electromagnetic factors: When reactive power or excitation current is adjusted, there is a significant change in the spark of the carbon brush. During the commutation of the exciter, the contact between the carbon brush and the commutator is poor, resulting in excessive contact resistance; The uneven thickness of the oxide film on the rectifier or slip ring causes an unbalanced distribution of carbon brush current; Or sudden changes in load, as well as sudden short circuits causing abnormal voltage distribution between commutator segments; Unit overload and imbalance; Unreasonable selection of carbon brushes, unequal spacing between carbon brushes; Quality issues with carbon brushes, etc.

Mechanical factors: Misalignment of commutator center and rotor imbalance; The unit experiences significant vibration; Insulation protrusion between commutator segments or protrusion of commutator segments; Poor contact caused by uneven grinding of the carbon brush contact surface or rough surface of the commutator; The surface of the commutator is not clean; The air gap under each reversing pole is uneven; Uneven or inappropriate spring pressure on the carbon brush; The carbon brush is too loose in the brush holder and jumps, or it is too tight and gets stuck in the brush holder. If the operating speed of the unit decreases or the vibration improves, sparks will decrease.

Chemical factors: Diesel generator sets operate in corrosive gases, or there is a lack of oxygen in the operating space of the unit. The naturally formed copper oxide film on the surface of the commutator in contact with the carbon brush is damaged, and the already formed, approximately linear resistance commutation no longer exists. During the process of re forming an oxide film on the contact surface, commutator sparks intensify. The commutator (or slip ring) is corroded by acidic gases or grease. Carbon brushes and commutators are contaminated, etc.

Maintenance of carbon brushes for generator sets

A. Operation inspection: Strengthen regular and irregular equipment patrol inspection work. Under normal circumstances, staff must inspect the generator carbon brush twice a day (once in the morning and once in the afternoon), measure the temperature of the collector ring and carbon brush with an infrared thermometer. During peak load periods in summer and when there are large fluctuations in reactive power and voltage, the temperature measurement interval should be shortened, and the replacement of new carbon brushes should be checked with emphasis. Conditional units should regularly use infrared thermal imagers to measure the temperature of the collector ring and carbon brush. And keep a record of the operating conditions of the equipment during the patrol inspection.

B. Maintenance and replacement: Conduct acceptance inspection on newly purchased carbon brushes. Measure the inherent resistance value of the carbon brush, measure the contact resistance of the carbon brush lead, and ensure that the resistance value meets the manufacturer's and national standards. Strictly adhere to the process of replacing carbon brushes, and the carbon brushes used in the same diesel generator must be consistent and cannot be used interchangeably. Before replacing the carbon brush, carefully grind the carbon brush to make its surface smooth. The brush should have a gap of 0.2 and 0.4 millimeters in the brush holder and move freely up and down inside the brush holder. The distance between the lower edge of the brush holder and the working surface of the commutator is 2-3 millimeters. If the distance is too small, it will collide with the commutator surface, which is prone to damage. If the distance is too large, the electric brush will jump and spark. Strive to achieve a carbon brush contact surface greater than 80% of the carbon brush cross-section. Replace frequently, but do not replace too many carbon brushes multiple times. The number of carbon brushes to be replaced at once should not exceed 10% of the total number of single poles. Carbon brushes with a top 3mm lower than the top of the brush holder should be replaced as soon as possible. The same type of carbon brush must be used each time the carbon brush is replaced, but attention should be paid to saving and fully utilizing the carbon brush. The replaced carbon brush must be measured for carbon brush current distribution using a DC caliper gauge and temperature tested using an infrared thermometer to prevent individual carbon brushes from overheating due to overcurrent. For obvious equipment problems such as protrusions and indentations on slip rings or commutator segments, it is necessary to use the opportunity of unit maintenance to tighten and grind them. Strengthen the quality of maintenance and operation control to avoid the leakage of turbine oil during unit operation due to poor maintenance quality or improper operation adjustment, which can be thrown onto the collector ring and increase the contact resistance between the carbon brush and the collector ring. The brush holder and brush holder should be carefully adjusted during major and minor repairs of the unit. When replaying and installing the brush holder, the angle and geometric position should be ensured to be in their original state. The sliding edge and sliding edge of the carbon brush must be parallel to the commutator.

C. Daily maintenance: Clean and blow dust frequently, keep the carbon brush and commutator slip ring clean, and clean them promptly in case of strong winds or after. Adjust the spring pressure frequently, and ensure that the pressure of the carbon brush spring meets the manufacturer's specifications, so that the carbon brush can withstand pressure evenly. Prevent individual carbon brushes from overheating or generating sparks, and prevent the occurrence of burnt or broken bristles. Any problems that arise during the operation of carbon brushes must be promptly resolved to avoid a vicious cycle that could jeopardize the normal operation of the unit. The carbon brushes used in the same unit must be consistent and cannot be used interchangeably. The maintenance personnel should be particularly careful during inspection and maintenance. The braids should be placed inside the hat, the cuffs should be fastened, and clothes and wiping materials should not be hung by the machine. When working, stand on an insulation pad and do not touch both poles or one pole and the grounding part at the same time, nor can two people work at the same time. When adjusting and cleaning carbon brushes and slip rings on a rotating motor, comrades with practical experience are required.