Transformer oil plays the role of insulation and cooling, so it must have certain electrical insulation strength in operation. In order to ensure the safe and reliable operation of transformer, in addition to taking protective measures to prevent premature aging of transformer oil in operation, oil sample test should be taken regularly to understand the state of oil quality in operation. For newly installed transformers, oil samples should also be taken for testing before the new transformers are put into operation. Transformer oil breakdown voltage test is one of the main items in transformer oil test. This paper only talks about some problems in the breakdown voltage test.

　　一、变压器油的绝缘强度（也称击穿电压或耐电压）除与天气干燥、潮湿有关外，还和试验试验时的温度及试验环境的大气压力有关在25℃以下时，因油中含有的水分成乳化状态，所以油的击穿电压的数值随温度的降低而降低但温度低于0℃时，因油中所有的水分解成了冰，油的击穿电压又将会有所提高。一般油温在65～80℃时击穿电压最高，这是因为油中水分成分子状态溶解于油。若温度超过80℃，击穿电压又开始下降，这是因为悬浮丁^油中的污染等等极性分子运动能量加快，从而增加了油中击穿的几率。此外，油的击穿电压还和试验环境的人气压力有关，压力增加，绝缘强度也随着增大。

　　1、 The insulation strength of transformer oil (also known as breakdown voltage or withstand voltage) is not only related to the dry and humid weather, but also related to the temperature during the test and the atmospheric pressure of the test environment. When the temperature is below 25 ℃, because the water contained in the oil is divided into emulsified state, the breakdown voltage value of the oil will decrease with the decrease of temperature. However, when the temperature is lower than 0 ℃, all water in the oil will decompose When ice is formed, the breakdown voltage of oil will be increased. Generally, the breakdown voltage is the highest when the oil temperature is 65-80 ℃, which is because the water in the oil is divided into molecular state and dissolved in the oil. If the temperature is higher than 80 ℃, the breakdown voltage will start to decrease again, which is due to the acceleration of the motion energy of polar molecules such as pollution in the suspended butane oil, which increases the probability of breakdown in the oil. In addition, the breakdown voltage of the oil is also related to the air pressure of the test environment, and the insulation strength increases with the increase of the pressure.
              

　　二、试验过程中的正常操作

　　2、 Normal operation during the test

　　在做变压器油击穿电压试验时，一杯油要打耐压数次，间隔的时间长则耐压打得越高，间隔的时间越短则耐压打得越低。这是冈为一般的试验设备在油击穿时，电极间隙中形成的电弧使油中产生游离带电粒子、气泡和碳粒等污杂留于电极间隙处，冈此在间隔时间较短再次试验时，这部分污杂极易形成桥路，致使数值偏低，而间隔时间越K，则这部分污杂因重力作用将逐渐分散离开电极间隙处，故试验数值随间隔时间增长而击穿电压数值提高。

　　In the breakdown voltage test of transformer oil, a cup of oil should be applied several times. If the interval is long, the withstand voltage will be higher, and the shorter the interval, the lower the withstand voltage. This is a common test equipment. When the oil is broken down, the arc formed in the electrode gap causes the free charged particles, bubbles and carbon particles in the oil to be left at the electrode gap. If the interval is short, these impurities will easily form a bridge, resulting in a low value. The more k the interval is, the more the dirt will gradually disperse away from the electrode due to gravity At the gap, the breakdown voltage increases with the increase of the interval time.

　　正常的操作应为：试油盛满后静置10分钟再作升乐试验，每次击穿后，用准备好的清洁玻璃棒在电极间拨弄数次或轻轻振动油杯，以达到破坏电极间新形成的电桥，再静置5分钟即可进行下次的试验。

　　The normal operation should be as follows: after the test oil is full, let it stand for 10 minutes and then perform Shengle test. After each breakdown, use the prepared clean glass rod to stir several times between the electrodes or gently vibrate the oil cup to destroy the newly formed bridge between the electrodes. The next test can be carried out after standing for another 5 minutes.

　　建议在变压器的高压侧串接一只限流电阻，以限制间隙击穿时的电流。这样可以缩短两次间隔的时间并得到准确的击穿电压数值。

　　It is suggested that a current limiting resistor should be connected in series at the high voltage side of the transformer to limit the current when the gap breaks down. In this way, the time between the two times can be shortened and the accurate breakdown voltage value can be obtained.

　　三、试验中击穿电压值变化情况的分析

　　3、 Analysis of the change of breakdown voltage in the test变压器油在做击穿电压试验时，一般一杯油做5次试验，取其平均值1. 初次击穿电压特别低的情况：第一次试验可能因向油杯中注油样时或注油前油杯电极表面不洁带进了一些外界因素的影响，使得第一次的数值偏低，因而需要进行第6次试验，取2～6次的平均值。

　　When transformer oil is used for breakdown voltage test, generally one cup of oil is tested for 5 times, and the average value is taken. 1. The initial breakdown voltage is particularly low: the first test may be caused by the influence of some external factors brought by the unclean surface of the oil cup electrode before or after oil injection, which makes the value of the first time low. Therefore, it is necessary to conduct the sixth test and take the average value of 2-6 times.

　　2. 5次击穿电压平均值逐渐升高的情况：一般在未经净化处理或处理不够彻底而吸有潮气的油样品中出现，这是冈为油被击穿后油品潮湿程度得到改善所致。

　　2. The average value of 5 times breakdown voltage gradually increases: it usually occurs in the oil samples which are not purified or not thoroughly treated and absorb moisture, which is caused by the improvement of oil moisture after oil breakdown.

　　3. 5次击穿电压值逐步降低的情况：一般山现在试验较纯净的油中，因为生成的游离带电子粒子、气泡和碳屑量相继增加，损坏了油的绝缘性能。

　　3. 5 times breakdown voltage gradually reduced: Generally speaking, in the pure oil tested, the amount of free band electron particles, bubbles and carbon chips increased successively, which damaged the insulation performance of the oil.

　　4. 击穿电压值两头偏低中间高的情况：这属于正常现象。

　　4. The breakdown voltage is low at both ends and high in the middle: This is a normal phenomenon.

　　目前，个别炼油厂供应的变压器油往往发生每次击穿电压与前次可能相差20-30%的现象，称为击穿电压的分散性，这不一定是试验仪器和方法的缺陷，而是由油样本身性质所决定的。这要通过提高油样的质量来改善。

　　At present, the phenomenon that the breakdown voltage of transformer oil supplied by some refineries may be 20-30% different from that of the previous one, which is called the dispersion of breakdown voltage. This is not necessarily due to the defects of test instruments and methods, but is determined by the nature of oil sample itself. This can be improved by improving the quality of the oil sample.