Design and Construction of Supplementary Module for Automatic Testing of Current Transformers

Current transformer is one of the important equipment of power systems, which is used for different purposes such as measurement, control and protection. This equipment probably encounters faults during its operation over time. As a result, some serious damages may happen to the Current transformer such as blasting of ct, ratio and phase displacement error increase. Therefore, it is necessary to evaluate it periodically. High voltage current transformers have several cores and many tests must be performed on each core, so numerous wirings must be done between the test device and the ct, which leads to higher human error rates while performing the tests. In addition, needed time for testing each ct is considerable and transformer is off load during the time. To solve these problems, a hardware interface called CT Analyzer or CT switch box is designed between test device and current transformer. This test equipment is made and manufactured in Iran and its specific brand name is KAVOSH T22. Moreover, this project includes a software sections as well as the hardware one. The hardware consists of a number of switches which connects ct and the test device according to the type of test, number of cores and taps of the current transformer. This solution has a significant effect on increasing the speed of testing and improving the results because of the impressive reduction of human errors. In the software section, proper decisions for the test are made and the embedded computer issues command to the relays automatically and then analyzes the results considering the standards and previous conditions of the same equipment if available. Finally, using this set up helps us calculate ratio error and phase displacement error of the ct based on ct parameters and its excitation curve. Furthermore, a new method is presented for the first time in our country, which enables the test device to assess and guess the technical parameters of the targeted ct without inserting any of the parameters. This feature has an exciting practical importance while replacing the existing current transformer with a new model.