Study On Current Transformer Analyzer Principle And Measurement Methods

Current transformers are current sensing and transmission equipment which are widely used in electric power system. It transimits the large current in primary side into a small standard current to the secondary measure, control and protection equipment use. Its accuracy and reliability is related to the safe, reliable and economic operation of electric power system. So the field testing of current transformer is an essential point to the safe of electric power system.Most traditional calibration technology for current transformers (CTs) is based on difference measuring method. Because of the limitation of the theory, it was difficult for field testing of CT. In this paper a new calibration method called voltage reciprocity method is proposed. The new method gains the ratio and phase error of CT by measuring the inner parameters of CT. According to the technology of designing intelligent instrumentation, the new testing instrument is based on DSP pocessor, adopts digital sampling and advanced signal processing technology. The requirements of field testing for CT were met by only one instrument.This paper first introduced several commonly used testing methods for the current transformer field testing, including traditional direct comparison measurement method and difference comparison measurement method, and focused on the new indirect measurement methods (low current extrapolation and voltage reciprocity), which emergences in recent years. And the advantages of the voltage reciprocity measurement were also pointed out. The structural design, device choice, hardware design and relate software choice of the high accuracy measure system was introduced according to the features of the signals. Then a Comprehensive error analysis about the measure system was made. The performance test results of the measure system were given also.The actual test results show that the high accuracy measure system design for the CT analyzer fully meet the requirements. It provided a scientific foundation for the design of CT field testing device.