来源:https://www.jnwdsh.com/ 日期:2020-09-09 发布人:woduanshihua
  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.
  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.
  2、 Normal operation during the test
  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.
  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.
  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.
  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.
  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.