A Device To Restrain The Transformers DC Magnetic Bias

In the early stage of HVDC transmission construction and the occurrence of a single pole fault, the system usually is operated with single pole-ground mode. Besides, the severe interaction in the sun results in the geomagnetic storms. Such situations mentioned above result in the current flowing in the earth and causing the transformers DC magnetic bias, which does seriously harm to the transformer itself and the power system. Thus it is necessary to restrain DC magnetic bias.The thesis gave a simply analysis of the reason why the transformers in AC system happened to be DC magnetic bias, and analyzed how such a phenomenon does harm to the transformers and the AC power system, then pointed out the importance to restrain the DC magnetic bias. Besides, it made a comparison of the methods to restrain the DC magnetic bias that usually used in the actual engineer, and presented a novel kind of topology based on electric potential compensation.Later on, the thesis designed every part of the topology, including rectifying circuit, filter circuit, protection circuit and so on based on the circuit theory and the actual requirements. Then it designed all working modes and corresponding control strategies by actual engineering. What is more, we ran the simulation based on pscad/emtdc when the AC system only happened to be DC magnetic bias without any fault to check the verification of the topology and its strategies.Then, the thesis gave the analysis and calculation of the parameters designed in the topology based on the control strategies above. Importantly, it pointed out the necessity of the protection circuit part, which has no influence on the relay protection of AC system. What is more, we ran the simulation based on pscad/emtdc when the AC system had an fault casually to check the parameters of the elements calculated above.At last, we made the device based on the control strategies and the element parameters above to restrain the DC magnetic bias. Then we conducted the corresponding experiments in 220V in lab, whose results met the result of the simulations above. Thus it proves to be right to repress DC magnetic bias, in addition we conducted another experiment to check the reliance of the protection circuit.All in all, the device to restrain DC magnetics in AC system designed in the thesis can achieve its targets predetermined, and thus it represents a new kind of device to the actual engineering.