Study On On-line Monitoring Technology Of Transformer Short-circuit Parameters

Transformer plays an important role in the power system.Its safe operation would directly affect the reliability and stability of power supply.Short-circuit impedance is an important technical parameter of transformer.It not only can be used to ascertain the presence of winding distortion,but also plays a key role in the economic operation of transformer and the calculation of relay protection setting values.At present,the traditional short-circuit test is still the main method for measuring the short-circuit parameters of transformer.This off-line method requires disconnection of the transformer from the power system.It not only affects the reliability of power supply,but also can not realize the real-time monitoring of short circuit parameters.In this thesis,online monitoring methods for short-circuit parameters of single-phase transformer and three-phase transformer are studied.For single-phase transformers,fundamental frequency components and orthogonal components of the currents and voltages are extracted by using MSOGI-FLL.The mathematical model of transformer in synchronous reference frame is established and a new method is proposed to monitor the short-circuit parameters based on instantaneous phase.Then,the transformer differential and integral equations are realized by the MSOGI-FLL.The short-circuit parameters can be calculated online based on these equations.Finally,the validity of the proposed methods is verified by simulation.The monitoring methods of single-phase transformer can be directly applied to Y/Y connected three-phase transformer.Therefore,this thesis is mainly studied on Y/△connected three-phase transformer.Firstly,the problem of triangle side circulation and unmeasurable winding currents can be solved by using the winding loop equations,and the short-circuit parameters can be calculated by using instantaneous phase method.In addition,based on sequence network equations of transformer,a new online monitoring method based on fundamental positive sequence components is proposed.Finally,the feasibility of these proposed methods is verified by simulation.For online monitoring of transformer winding parameters(primary,secondary resistance and leakage reactance),firstly,a new monitoring method of winding parameters based on load variation is presented by using the change of load.Moreover,during asymmetrical operation of transformer,the positive and negative sequence equations are constructed.A new online monitoring method for three-phase transformer winding parameters is proposed.Finally,the effectiveness of these methods is verified by simulation.At the end of this thesis,the hardware design of the online monitoring device for transformer short-circuit parameters is introduced and the validity of the online monitoring methods are verified by experiments.