| High impedance fault (HIF) is a sort of single-phase ground fault that can’t bedetected by the traditional relay-protection devices. Although there is little risk of thepower system, there will also exist dangerous of contacting to high voltage when people isclose, if not promptly treated. HIF is usually accompanied with arc, and it is easy to fire,causing damage to life and property. The accurately mathematical models, simulationmodels and protection algorithms of HIF on transmission lines are the persistent anddifficult problems.This paper summarized the fault features of HIF. A random current of fault，caused bythe arcing and nonlinear features of HIF， has certain features in transient and steady state.Based on the measured data and physical phenomena, a new mathematical model of HIFwas presented by numerical analysis methods and arc equations. Using EMTP, in the750KV transmission lines, the model of HIF includes a group of nonlinear time-varyingresistances and a dynamic arc resistance.Based on the fault features under different bands, this paper established HIFcomprehensive detection algorithms containing four algorithms. Comprehensive HIFdetection method is made up of fault-to-start discrimination and HIF detection. Thefault-to-start discrimination consists of fault start algorithm. This algorithm constructs twoband-pass filters with two different center frequencies using the wavelet packet transform.It achieves the criterion by comparing the spectral energy of transient signals within thesetwo bands. The HIF detection consists of fundamental algorithm, harmonic algorithm andhigh-frequency algorithm. The input of fundamental algorithm and harmonic algorithm is acurrent signal, calculating the magnitude by Fourier transform, using the harmonicalgorithm based on fault component of the mean to eliminate the interference ofbackground harmonic, then performing the frequency criterion and harmonic criterion. Theinput of high-frequency algorithm is a current signal with its high-speed sampling canperform the high-frequency criterion. A combination of three algorithms with the logical"and" is common to diagnose HIFFinally, by defining the concept of fault sets, the logic of comprehensive detectionalgorithms has been preliminarily explained. The mathematical models, simulation models and protection algorithms of HIF were simulated. It has clearly physical meaning, highcalculation reliability, and specific logic. |
