Design Of Capacitance Current Measuring Instrument For Distribution Network

The capacitance current of the distribution network system is not only an important parameter for accurately configuring the capacity of the arc suppression coil,but also an important parameter for analyzing the ferromagnetic resonance,and accurately measures the capacitance current of the distribution network system,so as to provide a basis for the accurate compensation of the arc suppression coil.When a single-phase ground fault occurs in the system,the ground point can be smoothly extinguished,and at the same time,the occurrence of ferromagnetic resonance over-voltage to avoid damage to the power equipme nt and ensure the long-term stable operation of the distribution network system.This article first explains the research background and significance of capacitance current measurement in distribution network systems,introduces the basic concept of capacitance current in distribution network systems,points out the dangers of single-phase ground faults in distribution network systems,and measures six common capacitor current measurements.The parameters of the instrument and the causes of the measurement errors are analyzed.Compared with several commonly used capacitance current measurement methods,the neutral point frequency signal injection method is selected as the basic measurement method of the capacitance current measurement instrument in this pape r.And give the overall design goals and design ideas of this article.Aiming at the problem that the existing capacitor current measuring instrument must be withdrawn from the arc suppression coil to measure,and the measurement accuracy is low and the measurement range is small when the arc suppression coil is withdrawn,this article analyzes the measurement principle circuit of the existing capacitor current measurement device in detail.The shortcomings of the equivalent model,a new equivalent circuit model is proposed,which fully considers the leakage resistance and leakage reactance of the grounding transformer or voltage transformer,so as to reduce the model error.In the data acquisition circuit,the full spectrum proposed by Professor Wang Zhaohua is used to suppress spectrum leakage.The new phase Fourier spectrum analysis method uses the phase invariance of ap FFT to accurately extract the initial phase information of the sampled signal,thereby reducing the sampling error.The calculation method of the capacitor current is derived in detail.A vector dual-frequency impedance method is proposed to exit the cancellation.When measuring arc coils,a vector dual-frequency admittance method is proposed for measuring arc coils on-line,thereby reducing calculation errors.In order to verify the correctness of the design idea of this paper,a physical current measuring instrument was developed.The circuit design of the main control unit with STM32F407VET6 as the core and the data acquisition unit with A D7606 as the core was introduced in detail.Give the software design flow of the main program module,data acquisition module and all-phase FFT module.Based on the distribution network system circuit model,a 380 V simulation experiment platform was built,and a large number of capacitance current measurement experiments were conducted.The capacitance current measuring instruments were measured at multiple substation sites.Combining laboratory simulation measurement data and substation field me asurement data,fully verified the feasibility and practicability of the capacitor current measuring instrument designed in this paper.