Research On On-line Calibration Technology Of Electronic Voltage Transformer

Digital substation is the product of adapting to the development of modern power market demand,and it is also the extension of the development of substation intelligent technology.Data acquisition,energy metering,relay protection,fault location,monitoring and other work in power system need electronic transformer as the intermediate hub to cooperate.The emergence of electronic transformer not only promotes the development of intelligent substation,but also provides a good soil for its further development.Because of its own structure and working principle,the electromagnetic voltage transformer has the disadvantages of complex insulation,narrow dynamic measurement frequency band,large volume and easy to occur ferroresonance.In addition,the output signal of the electromagnetic voltage transformer is analog signal,which restricts the development of the transformer to a certain extent,and also restricts the realization,application and development of digital substation.At present,electronic voltage transformer has been widely used in digital substation.However,due to the lack of technology and operation experience,problems such as accuracy,electromagnetic compatibility,insulation and so on have gradually appeared in the operation of electronic voltage.Therefore,in order to ensure the stable and reliable online operation of the transformer,it is necessary to monitor it in real time.In order to solve the instability of electronic transformer in field operation,not only the index of electronic voltage transformer should be calibrated before it is put into operation,but also real-time monitoring should be carried out after it is put into operation.In view of the problems of insulation and electromagnetic compatibility encountered in the application of electronic voltage transformers,and the cumulative influence of external environmental factors in use,the accuracy of transformers will change directly.Therefore,some scholars have proposed the calibration technology to check whether the accuracy of electronic voltage transformers is within the normal range,and how to verify the electronic voltage transformers safely,reliably,conveniently and accurately.Sensors are the key to calibration.The traditional calibration technology is designed to adapt to the traditional transformer,which is suitable for analog output and long calibration period.It cannot be completely and directly applied to the electronic voltage transformer calibration technology.In addition,the traditional calibration method is off-line calibration,that is,after the transformer exits the primary side line,it needs to be simulated by booster device after boosting voltage.This method not only needs complex work such as switching operation,but also has great influence on power failure.The online calibration technology proposed in this paper fundamentally solves the inconvenience and influence of offline calibration.The key technologies of on-line calibration include: 1)the selection,design and application of standard voltage transformers;2)how to connect standard voltage transformers to the line under the condition of ensuring the normal operation of the primary line is also the difficulty of the calibration system;3)high accuracy software algorithm to obtain the parameters of the signal and the difference between the two signals.According to the above three key points,the online calibration system of electronic voltage transformer is designed in this paper.The standard capacitor is a capacitor divider composed of SF6 cylindrical capacitor and precision NPO capacitor.The automatic lifting device with remote control is installed on the high voltage side.Through manual wireless remote control,the online voltage signal can be obtained safely and reliably.Considering the phenomenon of arc reburning and extinguishing when the elevator gradually contacts the live primary line,this process may lead to overvoltage breakdown of the divider capacitor.In addition,in the practical application of the capacitor divider in the field,the measurement deviation will be caused by the influence of external temperature and gas pressure.In this paper,the calculation,analysis and simulation of these two factors are carried out.The test is verified and reasonable measures are taken to ensure the stability,reliability and accuracy of the system.In order to meet the accuracy requirements of the calibration system,this paper designs and chooses appropriate hardware equipment,and designs a calibrator suitable for online calibration.The system calibration is completed by cooperating with Lab VIEW virtual calibration platform and PC.Software processing algorithm This paper chooses four-spectral line interpolation algorithm based on trapezoidal self-convolution window.The simulation results show that the algorithm meets the accuracy requirements of the system and is suitable for field applications.