Study On Transformer Main Protection Based On Fault Component Longitudinal Impedance

With the expansion of the power system's scale,it will be more important to ensure the reliable operation of the transformer for the safety of power system.The winding design of transformer usually adopts tangled winding,which is easy to cause short-circuit fault between turns of coils.In the outlet wiring place,it's often occurrence ground fault due to the line insulation question.When the transformer operating with no load,the electron magnetic fields in the inner space are coupled with each other,which made the fault state more complicated.Therefore,the transformer related protection algorithm needs to be improved.This thesis is based on the principle of longitudinal impedance protection,considering the problem of the current differential is easily disturbed by unbalanced current.The thesis puts forward the transformer protection algorithm based on the longitudinal impedance of fault phase component and the transformer protection algorithm based on the longitudinal impedance of fault sequence component.The simulation model of three-phase transformer is built to verify the protection algorithm.The core of the protection algorithm is calculating the voltage difference and current difference between the two sides of the transformer and obtain the longitudinal impedance then compare it with the leakage impedance of the transformer.The longitudinal impedance of the transformer is greater than the equivalent leakage impedance of the transformer when the transformer is out of the zone and no load closing.The longitudinal impedance is smaller than the leakage impedance of the transformer in case of fault inside the transformer.In the state of transformer faults,protection algorithm based on the stability of the electric triangle can correctly identify.When the current transformer is deeply saturated,the protection algorithm still has ideal sensitivity.When the transformer closing with no load,the protection is based on the numerical conversion relationship between the system impedance on the back side and the transformer's equivalent leakage impedance to resist the influence of inrush current on the protection algorithm.The above conclusions are verified by theoretical analysis and simulation,which prove the effectiveness of the protection principle.PSCAD/EMTDC software is used to build a three-phase transformer simulation model and MATLAB software is combined to verify the relevant algorithms of simulation data.The simulation results show that the protection algorithm based on the longitudinal impedance of the fault component can accurately identify the faults inside and outside fault zone,and is not affected by the saturation of current transformer and inrush current of transform.Among them,the phase protection algorithm has higher sensitivity in the case ofinternal turn-to-turn fault and can be used to identify inter-turn short circuit;the sequence component based protection algorithm can be used as the main protection algorithm of transformer for its reliable and stability.The principle of the above protection algorithm is simple and easy to set,which is not affected by the sampling frequency and has certain engineer application value.This thesis consists of 36 figures,9 tables and 70 references.