Research And Design Of New Electronic Voltage Transformers Based On Detecting Current Of Capacitor Directly

As power industry on the digital substation and smart grid’s constructionpromoted by power industry,electronic voltage transformer (EVT), which is one of thekey equipments for them, has been in lots of companies and universities’good gracesand is highlights and frontiers at home and abroad. This paper describes a new type ofelectronic voltage transformers and has applied for national patent.After review of electronic voltage transformer research at home and abroad, thispaper propose a new principle of the new electronic voltage transformer，based on thedetection of capacitive current to analysis high voltage,and the capacitive current canflow into signal processing device directly. the paper describes primary voltage’ssensing principle of the EVT and analysis its steady-state performance and transientprocess.After establishing the equivalent circuit to analysis of the frequencycharacteristics of the EVT;Analysising the influence of stray capacitance of the highvoltage capacitor for the EVT and proposing suppression methods stray capacitanceof test capacitor current-mode EVT suppression; proposing two schemes oftemperature compensation for the EVT,that one is using a thermistor closing to thecapacitor base to reflect the capacitor temperature and achieving a feedbacksignal,then sent to the signal processing device for temperature compensation,andanother is using the high voltage capacitor including positive and negativetemperature coefficient of capacitance to achieve the temperature compensationeffect.Then proposing a new method, combined power supplying method of obtainingpower from main power line by a small CT and by a capacitive voltage divider inparallel with the PT,to supply power for electronic current transformer with source.Focusing on the analysis of its structure, principle, syntony and the mechanism ofenergy transfering, as well as the influences of the auxiliary power to the EVT’saccuracy and reliability of the work. Finally Setting up the experimental platform todo steady-state error experiments and transient error experiments of the EVT in thelaboratory,producting the prototype to do high-pressure test, and adding acomplement of protection circuit and common-mode interference signal suppressionmeasures.The EVT, based on detecting current in capacitor, has the strongpoints such assimple insulation structure, high anti-interference ability, reliable work and without the power supply at the high pressure side,qualitative body is light, interference isstrong, and without the high pressure side of the power supply, high availability, andhas broad application prospects.So the EVT is of great practical value and prospects.