Study On Reliability Of Electronic Current Transformer

With the improvement of transmission capacitance and increasingly high voltage in power system, the magnetic saturation and insulation problem of traditional electromagnetic current transformer becomes more serious, and thus this does not meet the requirement that the network develops towards automation and digitized direction. The electronic current transformer has gradually become the substitute of the traditional electromagnetic current transformer. Whether the electronic current transformer can entirely replace the traditional electromagnetic current transformer depends on its reliability of long-term operation. Due to these, it is necessary and significant to theoretically evaluate the reliability of the electronic current transformers.In this thesis, the development of the electronic current transformers based on Rogowski coils and magneto-optic current transformer as well as the studies on it have been introduced systematically. The reliability of the two kinds of electronic current transformers has been evaluated by using both Monte Carlo method and the stress analyzing method. The devices in each unit contained in the electronic current transformer are determined and the formulae and parameters to calculate the working failure rate of these devices are presented. The failure probability and reliability of these two kinds of electronic current transformers as a function of time have been given, and also their average life has been calculated by using not only Monte Carlo method but also the stress analyzing method for the purpose of comparison.The reliability of the electronic current transformer based on Rogowski coils falls down to0.5when it is used for about5×104hours (～6years), and its average life is about6×104hours, i.e.6-7years. The reliability of the magneto-optic current transformer falls down to0.5after its use for about1×105hours (～11.6years), and its average life is about16x104hours, i.e.18years.The present work has shown that the magneto-optic current transformer is of longer average life and lower reliability, compared with the electronic current transformer based on Rogowski coils. In addition, the failure probability of the magneto-optic current transformer is smaller in the initial stage of its use and becomes much greater than that of the electronic current transformer based on Rogowski coils in the later stage of its use. The reliability and average life of the magneto-optic current transformer with the light source consisted of a silicon solar cell and a light-emitting diode are significantly higher than that with the light source formed by semiconductor laser. The average lives of the two kinds of electronic current transformers calculated by using Monte Carlo method are the same as those calculated by using the stress analyzing method.