Research On The Influence Of DC Bias Of Transformer On The Operation Characteristics Of Large Capacity Synchronous Compensator

With the development of high-voltage direct-current(HVDC)transmission,the dc-biased problem has been given more attention in recent years.Due to the influence of DC bias,the secondary side voltage of the transformer often contains higher harmonics.When a synchronous compensator that provides reactive support for a converting plant is connected to a DC biased transformer,the voltage containing the harmonics will be used as the terminal voltage of the synchronous compensator.The terminal harmonic voltage will affect the operating conditions of the synchronous camera.Therefore,it is of great significance to study the DC bias phenomenon of transformers and the operation of synchronous compensator.In this thesis,the actual power transformers and a 300MVar synchronous compensator are taken as research objects.The related research was carried out on the DC bias phenomenon of the transformer and the influence of DC bias on the synchronous compensator.The mechanism of DC bias magnetization was analyzed,and a field-path coupled time-step finite element model capable of accurately calculating transformer DC bias and synchronous compensator is established.The three-phase power transformers with different DC cores and different winding cores are simulated.The effects of core structure and winding connection group on DC bias are studied.The relationship between the winding connection group of the five-column transformer and the DC bias is analyzed.The rotor loss,excitation force and ability to absorb and emit reactive power under the influence of the terminal harmonic voltage was calculated.An experimental platform for DC biasing,and the accuracy of the established time-step finite element model was verified.Finally,the research results obtained in this paper show that:1)The three-column core structure and the triangular winding connection will significantly suppress the effect of DC bias;2)DC bias causes distortion of the waveform of the excitation current and induced electromotive force of the transformer,and increases the content of higher harmonics;3)When the compensator is connected to a transformer with DC bias,the higher harmonic voltage will be used as the terminal voltage of the compensator,which will increase the rotor loss of the camera and enhance the vibration of the compensator.