Research On Calibration System For Electronic Transformer With Digital Output

With the popularization of IEC61850 substation communication network and system standard and the construction of digital substation, electronic transformers have been widely used in power system. As the electronic transformer is different from traditional transformer in working principles and output modes, the calibration method for traditional transformer cannot be used to calibrate electronic transformer and making accurate measurement and calibration of electronic transformer in site has become an outstanding problem in the construction and operation of digital substation. So, it is necessary to develop a calibration system for electronic transformer with digital output to meet the current testing requirements.In this paper, the electronic transformer's structure and working principles are first introduced. Then, we mainly study on the Merging Unit's (MU) principles and its communication characteristics, analyzing and comparing related communication standards IEC60044-8 and IEC61850-9-1. After that, a new calibration system which meets the requirements of digital output of electronic transformer is designed by reference to the calibration standard of IEC60044-8 after making clear the new error definition of electronic transformer. Also the equipment selections, connection modes and function block diagram of the calibration system are proposed.In the part of error calculation, an error calibration algorithm based on the combined principles of the quasi-synchronous algorithm and Discrete Fourier Translation (DFT) is adopted. By increasing the sampled data quantity and algorithm's iteration number properly, the measurement accuracy is improved. This algorithm not only reduces the requirements of sampling signal frequency, but also restrains the impact of grid frequency fluctuation on the accuracy of calibration results effectively.In the end, a calibration platform is set up and its testing scheme of hardware and software is designed. At the same time, sampled value's (SV) model building is completed and the decoding of IEC61850-9-1 is done. On the base of that, the calibration system is tested by simulating field conditions. Experiment results show that the performance and accuracy of new calibration system based on the above-mentioned calibration algorithm is satisfied.