Study On Data Acquisition System Of Active Optical-Electric Current Transformer

Fast economic growth increases the requirement of electric power. Thus, modern electric power system must be safer, more stable and economical than before. And conventional current transformers (CTs) will not satisfy the current measurement for metering, control and protection in modern power system. New principles and new technologies must be studied and adopted. International Electrotechnical Commission (IEC) has established standards on electrical current transformers (ECTs), they are bases and directions for the development of new type current transformers. Active optical-electric current transformers (AOCTs) is a very important approach of ECTs. Study on it has been done for several years, and a lot of practical experience has been gained. Here, digital method for the current measurement of high voltage power system is studied, data acquisition systems (DAS) of AOCTs for both AC and DC is also designed. From IEC standards on ECTs, different methods for designing AOCTs are compared, and the one based on analog to digital conversion is chosen. This method can get high precision and short delay time. Furthermore, principle schematic of AOCTs is given, its main parts and their functions are introduced. Also the study object of this thesis is defined. DAS of AOCTs for AC and for DC have a few differences, because the properties of measured current and the requirement of AOCTs are different. The methods of sampling signals and dealing with the conversion results are the two main differences. This thesis compares these differences and focuses on AOCTs for AC. Based on the required performance, principles and methods for designing DAS are analyzed in detail, and error estimation of root-mean-square algorithm is also mentioned. DAS has many different characteristics, and a method to evaluate dynamic accuracy of DAS is introduced in this thesis. According to this method, experimentation is done on DAS of AOCTs for AC, and the dynamic accuracy is determined. Finally, the results of experimentations on AOCTs for both AC and DC indicate that the designs have satisfied the predefined requirement.