| As a kind of simple,cost-effective,and easy-to-install terminal,fault indicators with fault detection and location functions are widely equipped in distribution networks,which can expedite the fault identification process.Traditional fault indicators typically rely on the amplitude of fault phase current to detect faults.However,the fault current of single-phase to ground fault in distribution network is weak,and fault detection is difficult.Therefore,the use of zero-sequence current or voltage to determine the occurrence of faults,which requires synchronous data among the three phases.Additionally,with the increasing number of distributed generation and dual-source operation methods in distribution network,it is difficult for fault indicators that only rely on amplitude to accurately identify the phase-to-phase short circuit fault section.It is necessary for synchronous measurement between remote locations.Based on the background above,this paper focuses on the issues of three-phase synchronization and remote synchronization of fault indicators,and presents the following work:(1)Analysis of the operating principles of fault indicators and synchronous requirements.Firstly,the composition and principle of current fault indicators are introduced.And fault indicators with communication and telemetry functions,also named as "two-remote"(remote signaling and telemetering)fault indicators,are determined as the research object.Secondly,the synchronous requirements of "two-remote" fault indicators are analyzed,and traditional synchronous methods and their problems are identified.(2)Proposing a three-phase self-synchronization method for fault indicators based on"step mutation start+phasor symmetry relationship".Based on the start criterion of the sudden change of the fault phase voltage or current,the start deviation of the non-fault phase and fault phase recorded waveform data is identified by utilizing the symmetry relationship of the three-phase current phasor before fault moment,and then the start time is adjusted to align the three phases to achieve data synchronization.A distribution network model is established in MATLAB,and single-phase to ground fault simulations are performed to verify the correctness of the proposed method.(3)Proposing a remote fault indicator self-synchronization method based on the fault moment.Based on the fact that the propagation time of fault travelling waves in distribution lines can be ignored,the rationality of synchronization measurement by remote fault indicators using the fault moment as a reference base is analyzed.The feasibility of detecting fault moment by the moment of phase voltage and current and the influencing factors of errors are analyzed and demonstrated.MATLAB modelling and simulations of faults are performed for phase-to-phase short circuits to verify the feasibility of the proposed method.(4)Analysis of the application of self-synchronization methods in active distribution networks.An active distribution network model with distributed generations is established in MATLAB,and simulations of phase-to-phase short circuit faults are performed to obtain the fault waveforms of currents and voltages upstream and downstream of the fault point at various locations.The fault moment detection methods based on the change of phase voltage and current are separately used to detect fault moment,and then phasor calculations are carried out to verify the effectiveness of the remote synchronization method in distributed generation(DG)lines.The self-synchronization method of fault indicator data proposed in this paper does not require any external devices,and uses only software algorithms to achieve synchronization.It has the advantages of low cost,simple implementation,and small synchronization error,which making it suitable for engineering applications.Additionally,the fault voltage and current phasors obtained by the self-synchronization method provide new fault identification methods for traditional fault indicators. |
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