Detection Methods And Implementation Technology Of Half-wave DC Current

In field operation, DC injection line selection and positioning principle is a very effectivemethod in small current grounding fault line selection positioning. The group where I am inproposed the principle of the DC injection line selection positioning, when singlephase-to-earth fault occurs, a DC signal is injected to the fault line through the groundingtransformer, the DC signal injected method identifies the feeder and locates the fault point bydetecting the trace of the injected DC current signal. This shows that reliable detection of thehalf-wave DC current is one of the key technologies to implement the principle. In this paper,the problem is how to detect the half-wave DC current.In this paper, the DC current detection principles and programs are reviewed, andcomparing and summarizing several methods for power system fault detection. Among them,the DC high-current measurement methods include shunt principle、magnetic modulationprinciple、nuclear magnetic resonance principle、the principle of magneto-optical effect、hall-effect principle、Rogowski coil principle and so on. When detect micro-current, generallythrough a certain way to convert it to voltage to measure. The DC current program of existingdetection principle, characteristics, and their respective advantages and disadvantages arediscussed.This paper presents the method to detect the half-wave DC current by designing CToperating in the saturation. Its main feature is when single phase-to-earth fault occurs,injecting the half-wave DC current into the fault line through the primary side neutral point ofthe grounding transformer, the DC single flow along fault line and the point of failure into theground, meantime, the CT installed on the fault line is saturated, by anglicizing the electricalquantities of transformer secondary side to detect the current. This paper focuses on thespecial speed to be theoretically calculated saturation current transformer，including the corecalculations、winding calculations、current error calculation and the phase error calculation；Deriving the core magnetic circuit calculation by different soft magnetic materials composed；Discussing the impact of various factors on the current transformer saturation，like as primarycurrent waveform, the secondary circuit impedance, the core saturation flux density, corecross-sectional area, the number of turns and core remanence. Proposing a method to detect transformer saturation by analyzing the distortioncharacteristics of the secondary side induced current and voltage of current transformer. Usingthe maximum string of third difference discretization of the secondary current and voltagemod, the double-ratio criterion to diagnosis the secondary side voltage, so to detect the coresaturation and the half-wave DC signal.In this paper, the function, elements and simulation procedure of the power systemtransient simulation software ATP-EMTP is introduced briefly. The model of the single-phaseearthed fault in the distribution system is established using ATP software, discussing theimpact of various factors on the current transformer saturation by simulation; Verified theaccuracy of saturation through the simulation of one-way ground fault dual-ratio criterion...