Research On The Broadband Passive Circuit Model Of Capacitor Voltage Transformer

Capacitor voltage transformer(CVT) is a key equipment in the substation, which can be influenced easily by the over-voltage impact caused by the lightning or switching operation. Considering the parameter design of CVT is only in view of the power and harmonic frequencies, the traditional circuit model can't describe the high frequency characteristics, as a result, it will cause measurement error respected to the MHz level signals(such as lightning). In this paper, an accurate CVT broadband passive circuit modeling method is proposed which can be used to analyze the over-voltage in the substation.According to the conventional macro-modeling method, the vector fitting method is used to fit the measurement results as the rational fraction, in which the overall passivity of fitting results can be guaranteed, however, the passivity respected for all the sub-items cannot be guaranteed easily. In order to solve this problem, a "merger certain sub-items passivity treatment method" is proposed according to the two-port admittance matrix in this paper, which will be helpful to reduce the complexity of in the following network synthesis process. Numerical examples are given and verified the correctness of the method.Based on the intensive study of the multi-port Brune network synthesis method, a simplified method using to calculate the minimum value problem respected to the conductance matrix extraction is proposed and the analytical formula of the elements of the susceptance matrix H is also derived, which can simplify the traditional iterative optimization algorithm excessive in the extreme value problem as for the two-port circuit.Combined with the traditional network synthesis method with the multi-port Brune method, a new broadband passive network synthesis method is proposed, which cannot only guarantee the passivity but also can be established easily. Taking advantage of this method, a novel broadband passive equivalent circuit model of a CVT is established. By comparing the simulation result with the measurement testing under the lightning excitation, the correctness of the model is verified.