The purpose of filtration is to remove the moisture and impurities in the oil, improve the electrical strength of the oil, protect the paper insulation in the oil, and improve the physical and chemical properties of the oil to a certain extent.

配电电力变压器大都安装在露天环境中，绝缘油(变压器油)受外界杂质、和空气接触以及设备本身运行温度较高的影响，使油的质量逐渐变坏。变质后的绝缘油(变压器油)就不会起到应有的绝缘、冷却作用。为防止因油质变坏而致使的安全运行受到影响，应对正常运行的配电定期采油样进行化验分析，并根据分析结果对油进行相应的处理。配电运行油化学监督的检验周期规定为至少3年一次。常规检验项目包括酸值、水溶性酸、闪点、击穿电压、外状。

Distribution power transformers are mostly installed in the open air. The quality of insulating oil (transformer oil) is gradually deteriorated due to the influence of external impurities, contact with air and high operating temperature of equipment itself. The deteriorated insulating oil (transformer oil) will not play its due role in insulation and cooling. In order to prevent the safe operation from being affected due to the deterioration of oil quality, the oil samples in normal operation should be tested and analyzed regularly, and the oil should be treated according to the analysis results. The inspection cycle of the chemical supervision of distribution operation oil shall be at least once every 3 years. Routine inspection items include acid value, water-soluble acid, flash point, breakdown voltage and appearance.

应注意的是：若设备经常带负荷比较高，应在规定试验周期的基础上，增加检验次数;若经检验的项目某些指标明显接近所控制的极限值时，也应增加检验次数;由于运行油的质量随老化程度和所含杂质等条件的不同变化很大，通常不能单凭一种试验项目作为评价油质状态的依据。应根据所测定的几项主要特征指标进行综合分析。

It should be noted that if the equipment is often loaded with high load, the inspection frequency shall be increased on the basis of the specified test cycle; if some indexes of the inspected items are obviously close to the controlled limit value, the inspection times shall also be increased; Because the quality of running oil varies greatly with aging degree and impurities, it is usually impossible to evaluate the quality of running oil only by one test item. Comprehensive analysis should be made according to several main characteristic indexes.
   

1.酸值 其超极限值为大于0.1mgKOH/g。超出极限值的可能原因有4种：超负荷运行;抗氧化剂的消耗;补错了油;油被污染。对酸值超出极限值可采取如下对策：调查原因，增加试验次数，测定抗氧剂含量并适当补加，进行变压器油油的再生处理，若经济合理可做换油处理。

1. The over limit value of acid value is more than 0.1mg KOH / g. There are four possible reasons for exceeding the limit value: overload operation; consumption of antioxidants; wrong oil supplement; oil contamination. For acid value exceeding the limit value, the following countermeasures can be taken: investigate the causes, increase the number of tests, determine the content of antioxidant and add appropriately, carry out the regeneration treatment of transformer oil, if it is economical and reasonable, it can be replaced.

2.水溶性酸 其超极限值为小于4.2。超出极限值的可能原因有2种：油质老化;油被污染。对水溶性酸超出极限值可采取如下对策：增加试验次数，并与酸值比较查明原因。进行油的再生处理，若经济合理可做换油处理。

2. The over limit value of water-soluble acid is less than 4.2. There are two possible reasons for exceeding the limit value: oil aging and oil contamination. The following countermeasures can be taken for the water-soluble acid exceeding the limit value: increase the test times, and compare with the acid value to find out the reason. Carry out oil regeneration treatment. If it is economical and reasonable, it can be replaced.

3.击穿电压 其超极限值为小于20KV。超出极限值的可能原因有2种：油中含水量过大;油中有杂质颗粒污染。对击穿电压超出极限值可采取如下对策：查明原因，进行真空滤油处理、板框压力式滤油机处理或更换新油。一般选用ZJB真空滤油处理后油的击穿电压要求大于50KV。

3. The over limit value of breakdown voltage is less than 20kV. There are two possible reasons for exceeding the limit value: the water content in the oil is too high; there are impurity particles in the oil. For the breakdown voltage exceeding the limit value, the following countermeasures can be taken: find out the cause, carry out vacuum oil filtration treatment, plate and frame pressure oil filter treatment or replace new oil. Generally, zjb vacuum oil filter is selected, and the breakdown voltage of oil after treatment is required to be greater than 50kV.

4.闪点 其超极限值为小于130℃。或者比前次试验值下降5℃。超出极限值的可能原因有2种：设备存在局部过热故障;补错了油。对闪点超出极限值可采取如下对策：查明原因，消除故障;进行真空滤油机脱气处理，或进行换油处理。

4. The over limit value of flash point is less than 130 ℃. Or 5 ℃ lower than the previous test value. There are two possible reasons for exceeding the limit value: local overheating fault of the equipment; wrong oil supplement. The following countermeasures can be taken for the flash point exceeding the limit value: find out the cause and eliminate the fault; degassing the vacuum oil filter or changing the oil.

5.外状 如果外观目测油不透明，有可见杂质或悬浮物。或油色太深，则为油外观异常。外观异常的可能原因有：油中含有水分、纤维、碳黑及其它固体物。对外观异常的油应采取以下对策：若油模糊不清、浑浊发白，表明油中含有水分，应检查含水量。若发现油中含有碳颗粒，油色发黑，甚至有焦臭味，则可能是内部存在有电弧或局部放电故障，应与其它试验结合，调查原因，排除故障。若油色发暗，而且油的颜色有明显改变，则应注意油的老化是否加速，可结合油的酸值试验分析，或加强油的运行温度的监控。

5. Appearance: if the oil is opaque by visual inspection, there are visible impurities or suspended solids. Or oil color is too deep, oil appearance is abnormal. The possible causes of abnormal appearance are: moisture, fiber, carbon black and other solids in the oil. For the oil with abnormal appearance, the following countermeasures should be taken: if the oil is fuzzy, turbid and white, indicating that the oil contains water, the water content should be checked. If it is found that the oil contains carbon particles, the oil color is black, and even has a burnt smell, it may be that there is an arc or partial discharge fault inside the oil. It should be combined with other tests to investigate the cause and eliminate the fault. If the color of the oil is dark and the color of the oil changes obviously, it is necessary to pay attention to whether the aging of the oil is accelerated. It can be combined with the acid value test and analysis of the oil, or strengthen the monitoring of the operating temperature of the oil.