Research Of Vital Problems On Electronic Air-core Current Transformer

Air-core current transformer is one of the three kinds of new-style electronic current transformers. It has many potential benefits over conventional current transformers such as enhancement in signal bandwidth and dynamic range, large range of measurement, light weight, lower price, ease of manufacture and so on, so it will be widely used in power electrical system.Firstly, the basic theory and general conventional structure of electronic air-core current transformer were briefly described. The main reasons why air-core current transformer has not been used widely in exactly metering were discussed, through which three problems were concluded including new structures and new manufacture technology of Rogowski coils which can be precisely design and produced, more reliable power-supply systems with long life, and industrialization of air-core current transformers applied in different rating currents.According to the problems discussed above, a new means was presented to design Rogowski coils based on Printed Circuit Board. Two new Rogowski coil structures based on PCB were designed. The two Rogowski coils are easy to be manufactured without handwork and can be applied in mass production. The mutual inductance and self-inductance were deduced. The properties of two new Rogowski coils based on PCB and conventional hand-made Rogowski coil were tested, through which the two new Rogowski coils were proved to have high precision and reliable repeatability and be immune to temperature changing. The usual power-supply means, such as power-supply system based on CT and optical power-supply system, have many disadvantages, so the new power-supply mean based on microwave was presented. The elementary structure of wireless power-supply system used in electronic current transformers was designed. The feasibility was discussed through tests. In practice, there are so many specifications that all parts of the system must be restricted in order to predigest design and manufacture process and reduce the price. All electronic air- core current transformers applied in different rating currents must have the least difference as soon as possible, which is the last and vital step to realize mass production and mass application.A Rogowski coil provides both metering signal and protecting signal successfully. The range of measuring involves all specifications from 20A to several amperes. The designed electronic air-core current transformers can meet the requirements of 0.2S Class. It is a successful experiment of electronic air-core current transformer used in exact measurement. Finally, the designed samples were tested, and the results of an electronic air-core current transformer, whose rating current is 300A, were given. Through tests, the systems were proved to have the property of 0.2S Class and achieve the desired requirements.