Research On The Fault Location Method Of Ground Wire Melting Ice In DC Transmission Line

The large capacity and long-distance transmission characteristics of China’s power grid require high-voltage DC transmission lines to pass through a large number of valleys and hilly areas.In these areas,if severe cold weather comes,the transmission lines are prone to icing.Considering that the icing on overhead ground wires located in the same environment as the transmission lines will be more severe,in order to reduce the impact of icing on overhead ground wires,this article uses DC ice melting method to conduct ice melting on overhead ground wires.In the process of ice melting for the overhead ground wire,the overhead ground wire is insulated from the poles-towers along the line,so the ground wire can be treated as a DC transmission line.If a fault occurs in the ground wire for ice melting,the electromagnetic coupling of the parameter asymmetric system consisting of the ground wire and the highvoltage DC transmission line on the same tower will become complex.In order to improve the reliability and stability of ice melting for the ground wire,this paper deduces the complete process of phase mode transformation for this multi conductor transmission system,obtains a decoupling method suitable for this system,and acquires the phase mode transformation decoupling matrix that transforms the coupled phasor traveling waves into mutually independent modulus traveling waves,to realize decoupling of the system.Based on the decoupling parameters and the frequency-dependent characteristics of the system,relevant conclusions can be obtained,that is,the air mode traveling wave velocity between the decoupled DC transmission line and the ground wire is similar to the air mode traveling wave velocity between the poles of the two types of lines,while the decoupled zero mode traveling wave velocity is much smaller than air mode traveling wave velocity,but its attenuation characteristics are more severe than the air mode,and the air mode hardly attenuates.Therefore,the air mode component can be used,its wave velocity is taken as the transient traveling wave velocity of DC conductor for single-terminal traveling wave fault location.This article considers the high cost of high-frequency acquisition devices and the limited economic cost in practical engineering,and the additional traveling wave fault location device installed separately on the ground wire is not economical enough.Therefore,a grounding fault location method based on DC conductor electrical quantity is proposed.Due to the difference of the equivalent circuit for the fault point and the end point of the DC transmission line,the polarity of the reflected wave from the fault point and the refracted wave from the opposite end are not consistent,and in view of the fact that the transient traveling wave in the field actual engineering often contains a lot of noise,it is easy to fail only by using the single time-frequency domain detection method.Therefore,this paper proposes a single-terminal traveling wave fault location scheme of DC conductor based on wavelet transform and progressive kurtosis to indirectly locate the grounding fault of insulated ground wire during ice melting.Both wavelet transform and progressive kurtosis can reduce the adverse effects of electromagnetic noise.Using wavelet transform or progressive kurtosis alone to calibrate the required traveling wave head is easily confused with noise,so combining the two can achieve accurate calibration of transient traveling wave head,where progressive kurtosis can calibrate the initial wave head,wavelet transform and progressive kurtosis can calibrate the second wave head,and judge the polarity of the initial wave head and the second wave head by wavelet transform.Then identify whether the second wave head is from the fault point or the opposite end.According to the actual DC transmission project,this paper uses PSCAD/EMTDC electromagnetic transient simulation software to build the line model of the DC ice-melting parameter asymmetrical system on the same tower,and carries out a large number of ground fault simulations for ground wire with different transition resistances and fault distances.The simulation results show that the proposed single-terminal traveling wave fault location method is effective and feasible.