The Research And Design Of Calibration System For Electronic Transformer With Digital Output

With the nation-building of high-voltage power transmission and intelligent substation during the12th Five-Year-Plan, the digital and intelligent in power equipment are getting higher and higher. More and more people use electronic transformers instead of traditional electromagnetic transformers, the electronic transformers are becoming important equipment in smart grid measurement and protection. Before the electronic transformer is applied to power system, calibrating the accuracy of digital output is significant. So most of research departments, universities and companies are researching and designing the related equipment.Based on the national standard IEC61850-9-2, this paper builds a calibration system of electronic transformers with the technology of FPGA and LabVIEW, which can be used to check the digital output of the electronic transformers under0.2level. This system employs traditional high accuracy electromagnetic transformers to be the reference and receive as well as analyze the IEC61850-9-2data of merged unit attached to the electronic transformers, and then it is also used to calculate the amplitude error and phase error.First of all, the paper introduces the model of electronic transformer’s digital output and principle of error analysis, and gives the whole design frame of calibration system. Then paper states the design process of data collection and transmission as well as the calculation method of error in detail. FPGA is used as the main controlling chip in the part of data collection and transmission. For the checking channel, receiving and analyzing the IEC61850-9-2data of electronic transformer are finished through the Ethernet LAN9215. For the standard channel, the control circuit of24bits A/D transformation chip AD7760is designed, which is used to transform the analog output of traditional electromagnetic transformer to digital output. In order to achieve synchronous sampling, sampling pulse synchronization module based on GPS second pulse is designed. At last, the control circuit designing of USB transformation chip CY7C68013A is accomplished, which is used to transform the two channels’data. The error calculation of calibration system employs the DFT algorithm based on fourth-order rectangular self-convolution windows in Lab VIEW. At the same time, the system’s interactive interface is designed, which can set configuration information and show error results.Finally, referring to the calibration test of National High-voltage Metering Station, the accuracy test of calibration system platform is carried out with related equipment. It can be proved that the design of calibration system can satisfy the accuracy requirements through analyzing several experimental data.