| Current transformers,as important measuring elements of power systems,need to be calibrated regularly according to national standards.The current calibration methods of current transformers are mostly off-line calibration methods,which not only take time and effort,but also affect the normal operation of the power system.Therefore,this paper proposes a GPS-based online calibration technology of current transformer and constructs a current transformer online calibration system,which solves the problem of asynchronous data collection during online calibration and improves the accuracy and convenience of current transformer calibration.First of all,in order to solve the problem of asynchronous data collection in online calibration,this article introduces GPS timing.Because the factors that affect the accuracy of GPS timing are transmission delay and inherent delay,analyze and propose solutions for the two.Aiming at the transmission delay,a dual-frequency ionospheric model was established to obtain the delay values at different times.For the inherent delay,the receiver’s absolute calibration method was used to design an all-pass filter circuit to compensate,and reasonably adjust the circuit parameters to solve different acquisitions out of sync.Secondly,a high-speed synchronous acquisition system based on on-line verification of GPS timing current transformers was built through hardware and software design.Among them,the hardware design includes GPS timing module,FPGA module,signal amplifier module,AD conversion module,temperature compensation module,voltage monitoring module,transmission link and so on.We use LabVIEW to develop a signal acquisition program and a program for synchronous data processing.A synchronous data acquisition experiment was performed,and the results verified the precise synchronization and accuracy of the synchronous acquisition system.Thirdly,the adapt Kalman Filter(AKF)algorithm is applied.An algorithm of data processing based on CNN-AKF is proposed in conjunction with the Convolution Neural Network(CNN),which improves the filtering effect and calibration of synchronously collected data.Both the accuracy and effectiveness of the algorithm is verified by simulation.Finally,the high-speed synchronous acquisition system designed in this paper is used to build an experimental platform with standard current transformers,data acquisition systems,signal amplifiers and other equipment.The online current transformer verification experiment is completed,and the accuracy and feasibility of GPS time-based current transformer online calibration technology is verified. |
