Research On Electronic Voltage Transformer Based On Capacitive Voltage Divider

Voltage transformer is a very useful and important device in electric energy measuring and relay protection. There are three types of voltage transformers used in power system: PT-potential transformer, CVT-capacitive Voltage transformer, EVT-electronic voltage transformer. As voltage level of transmission lines increasing, PT and CVT have several draws at extra-high voltage. Compared to PT and CVT, EVT has the advantage such as no saturation resonance, high degree of insulation, high precision, wide bandwidth and lower cost. So electronic voltage transformer replacing PT and CVT will be the certain developing tendency. This paper is mainly about electronic voltage transformer based on capacitive voltage divider.Precision of sensor mainly decides the precision of EVT, according to this paper, capacitive voltage divider is a good choice as the sensor of EVT, especially at high voltage grades. The principle of capacitive voltage divider is analyzed, this paper also analyses stray capacity and temperature's impact on capacitive voltage divider, then studies transient characteristic of electronic voltage transformer based on capacitive voltage divider, and concludes the method of improving the stabilization and transient characteristics.As a major part of EVT, data collection and signal processing system is also analyzed in this paper, and this paper concentrate on the research of filter, digital integrator, phase compensation, a lowpass filter and a digital integrator scheme based on FPGA are proposed.Merging unit is an important component of the interface between electronic instrument transformers and the baylayer device of substation, the merging unit's functional characteristics are analyzed in this paper. Then this paper studies the function of synchronization of merging unit.A 110kV electronic voltage transformer prototype has been developed and tested, results show that the measurement accuracy could reach class 0.2. At last a calibration system based on LabVIEW for electronic instrument transformers is given, This calibration system can determine such performance indices of electronic instrument transformers as ratio error, phase-angle error accurately. The experimental results show that the system is stable and has high accuracy.