Hybrid Operation Of Multi-type Current Transformers And Its Influence On Differential Protection

The paper is based on the analysis of the transient charact eristics differences of different types current transformers,developing the physical models of electronic current transformer,TPY-level current transformers and 5P-level current transformers.On this basis,building the hybrid operation testing platform of multi-types current transformer,studing the factors influencing the hybrid operation characteristics of the multi-type current transformer,analyzing the influence of the mixed operation of the current transformer on the differential protection from two aspects of the saturation characteristics of the P class current transformer and the tail current characteristic difference of the different current transformer,putting forward the corresponding improvement measures.First of all,this paper analyzes the difference between the characteristics of different types current transformers in theory,investigating the hybrid operation mode of different types current transformers in the engineering site,studying the dynamic testing technology of multi-type current transformer hybrid operation,developing electromagnetic current transformer mode(Including the P-level and TPY-level)and the electronic current transformer mode are equivalent to actual current transformer,testing the key parameters of the physical model of the multi-type current transformer,the results show that the parameters of the physical model and the engineering current Transformer parameters have a good consistency.And on this basis to build multi-type current transformer hybrid operation dynamic test system of a line protection,multi-type current transformer hybrid operation dynamic test system of transformer protection and multi-type current transformer hybrid operation dynamic test system of bus protection.Secondly,taking the line protection hybrid system as an example,simulating the fault in the circuit area,and the fault recorder is analyzed by the MATHCAD algorithm.Studying the transmission characteristics difference of multi-type current transformers from harmonic and non periodic components when the electromagnetic current transformer is under the normal operating condition,the slight saturation and the severe saturation,and obtaining the variation rule of the harmonic content and periodic component in the secondary current when the P-class current transformer is under different saturation degree.Finally,analyzing in combination with dynamic mode test waveform the differential protection operation characteristics of multi-type current transformer hybrid operation.Under the condition of normal transmission,slight saturation and severe saturation of electromagnetic current transformer,analyzing the differential current and the braking current curve of hybrid operation,and the differential protection ratio braking characteristic,the study shows that the current transformer saturation time is less than 5ms,the differential protection device has the risk of malfunction.Again,avoiding the serious saturation of the current transformer,the improvement of the differential protection device to identify the severe saturation criterion and avoiding the influence of the "trailing" current on the differential protection based on the hybrid operation.The corresponding measures are adopted to prevent the risk operation of the differential protection based on the hybrid operation,improving measure has been tested in the dynamic test platform.