Effect Mechanism Of Velocity On Discharge Caused By Metal Particles In Flowing Transformer Oil

With the rapid development of power grid, China has reached an international level in transmission capacity, equipment and technical level and higher requirements have been put forward for the performance and reliability of transmission equipment. As the key equipment of power transmission and transformation equipment, large power transformer plays an important role in the safe and stable operation of the power system.Inner insulation degradation is a great source of transformer faults and PD(Partial Discharge) is one of important factors of Inner insulation degradation of power transformer. Therefore, insulation property can be analyzed by PD monitoring in transformer. Different types of impurity particles can be found inside due to manufacturing, transportation, installation and operation of power transformer and metal particles is the most harmful to the inner insulation performance. Currently research is focused on the influence of impurity particles in static transformer oil. But transformer oil is always in flow state instead of in static state,so further research should be made on the PD characteristics of metal particles in flowing transformer oil.According to the operating conditions and defect model of power transformer in practical engineering. Discharge device of micro-particle discharge simulation test system has been designed which can reflect the structure of real transformer oil duct and provide flowing transformer oil. At the same time, theory of discharge and breakdown due to metal particles has been established and mechanism research of effect of velocity on discharge and breakdown caused by metal particles in transformer oil has also been carried out. A large number of UHF(Ultra High Frequency) PD signals at different velocities have been collected by UHF method and influence of velocity on PD and breakdown caused by metal particles in transformer oil has been discussed. The main work and innovative achievements are shown below.(1) According to the structure of real transformer oil duct and the internal electric field distribution, discharge device of micro-particle discharge simulation test system has been designed and physical model of suspended metal particle defects has been established. At the same time, plenty of experiments have been carried out to obtain UHF PD data of suspended metal particles in insulating oil on the PD test platform.(2) The althor established a discharge model of metal particles in transformer oil and analyzed the force on metal particles in the oil duct. Trajectory and distribution of metal particle swarm motion in transformer oil were simulated by FLUENT simulation software and the movement process of metal particles under flow and static state was analyzed. The movement of metal particles in flowing transformer oil is proposed, which includes 4 kinds of states: slow rolling, small oscillating, sharp jumping and horizontal flowing.(3) The PRPD(Phase Resolved Pluse Sequence) and frequency analysis spectrum of metal particles' discharge in transformer oil at different velocities were built. PDIV(Partial Discharge Inception Voltage) discharge voltage, number and amplitude of PD, interval of adjacent discharge pulse, tequivalent discharge quantity were extracted, which can be the characterization of discharge intensity. Based on the discharge and breakdown mechanism of metal particles in transformer oil, the influence mechanism of discharge characteristics variation with oil velocity was analyzed. Eventually, it was carried out that the insulation performance of power transformer can be optimized by adjusting the flow velocity of transformer oil, which lays a solid foundation for the improvement of discharge theory in liquid insulation medium.