交直流复合电压下变压器油中电弧放电及产气特性

Arcing Discharge and Gas Generation Characteristics of Transformer Oil Under Combined AC and DC Voltage

换流变压器是直流输电工程重要设备之一,其阀侧绕组承受的电压较为复杂,包括直流、交流、交直流叠加以及极性反转等多种电压形式。因此在构建交直流复合电压系统的基础上,采用典型针板电极模型,对变压器油在交流、直流和交直流复合电压条件下的电弧放电和产气特性进行研究。试验表明变压器油在交直流复合电场和直流电场下的绝缘性能较交流电压下差。交直流复合电压下油隙的击穿电压与其纹波因数有关,纹波因数越小击穿电压越低。引入小桥理论的极化过程很好地解释了这一物理现象。同时,不同类型的电压作用下放电产生的油中溶解气体体积分数(每种气体与总气体的体积比)一致,说明判断交流变压器的改良三比值法故障类型判断方法对交直流叠加电压和直流电压下的电弧放电故障仍然适用。但是由于直流和含有直流分量的电压更容易产生油中放电,换流变压器的油中溶解气体体积分数(换算后每升油中所溶解气体的体积)的注意值和气体增长率注意值应有别于传统交流变压器。

The valve winding of converter transformer withstands several types of voltage, including AC, DC, combined AC-DC and polarity reversal voltage. We constructed a combined AC-DC high voltage source, and studied the arcing discharge and gas generation characteristics of transformer oil by using needle-plate model. The results show that oil gap under DC voltage and combined AC-DC voltage is much easier to breakdown than that under AC voltage, and the breakdown voltage is related to the ripple factor. The lowerer the ripple factor is, the lower the break- down voltage will be. A polarization process of the bridge theory is adopted to explain this physical phenomenon. The ratio of every kind of gas is the same under AC, DC and combined AC-DC voltage, showing that the three-ratio method is still suitable for arcing discharge under DC and combined AC-DC voltage. However, considering that discharge happens much easier under DC voltage, the noticed value of dissolved gas in oil and its growing speed for converter transformers should be different from that of AC transformers.