Abstract:On the basis of analyzing high-voltage direct current (HVDC) transmission system and its fault superimposed circuit, the direction of the fault components of the voltage and the current measured at one end of transmission line is certified to be different for internal faults and external faults. As an estimate of the differences between two signals, relative entropy is an effective parameter for recognizing transient signals in HVDC transmission lines. In this paper, the relative entropy of wavelet energy is applied to distinguish internal fault from external fault. For internal faults, the directions of fault components of voltage and current are opposite at the two ends of the transmission line, indicating a huge difference of wavelet energy relative entropy; for external faults, the directions are identical, indicating a small difference. The simulation results based on PSCAD/EMTDC show that the proposed pilot protection system acts accurately for faults under different conditions, and its performance is not affected by fault type, fault location, fault resistance and noise.
The railway distribution system is a neutral noneffectively grounded medium-voltage network. An advanced fault-location system for this distribution network, called the railway distribution network fault location system, is proposed in this paper. This fault-location system is based on tracing the superimposed signal and the work principle, simulation results, and field tests of the location system are presented. It is able to identify the fault location in a fast and accurate way. Compared with other conventional superimposed signal-based schemes, the system's performance is improved by employing the inject and fault-current detect sensor (IFCDS) to trace the fault signal and wireless to transmit detect information. The IFCDS, which permanently hangs on feeders, is based on the wireless sensor networks technology, so it can network automatically in a certain range, and improve the flexibility of the communication subsystem. Through analyzing the uploaded information by the fault-location computer in the substation, the fault point can be located. Issues of superimposed signals, such as optimal frequency choice, impact of tapped load, fault distance, and fault resistance, and so on are of concern. Through simulation in PSCAD/EMTDC, these issues are fully discussed. At last, the tests in the field show that the system has simple principle, high reliability, fast location speed (usually less than 15 min), and high accuracy (location error is less than 0.5 km).Index Terms-Fault location, neutral noneffectively grounded system, railway continuous transmission line (CTL), S-injection method, wireless-sensor networks (WSNs).
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