High frequency passivity circuit model of potential transformers

Very fast transient overvoltage generated in gas insulated substation (GIS) will introduce into secondary by potential transformer (PT), and which will affect secondary equipment, so it must be analyzed. PT circuit model according to measured frequency domain network function could be implanted into EMTP or PSPICE, but if the model has active element, then the simulation maybe unsteady. For solving the problem, a method to obtain PT high frequency microscopic passivity circuit model is proposed. First, the method uses vector fitting to obtain steady Foster formula, and then active set method is used to solve quadratic programming with constraint to obtain passive Foster formula. At last, a circuit synthesis method for rational functions is applied to build microscopic passive circuit model. The effectiveness of the method is verified by the comparison of network function before and after passive adjustment.