This paper investigates the use of the norm criteria in the electromagnetic time reversal (EMTR) technique to locate faults in transmission lines. The energy root criterion and amplitude peak criterion, derived from 2-norm and ∞-norm, are considered and discussed contrastively. It is shown that both considered norm criteria can effectively be used in an EMTR method to locate faults. The ∞-norm originates from temporal and spatial variation of norm quantity of voltage/current wave propagation in the EMTR process. It is proven that the ∞-norm criterion makes use of the EMTR refocusing property of voltage/current waves propagating along transmission lines. In the extremely noisy circumstances, the ∞-norm criterion shows better robustness against noise compared to the 2-norm. It can locate the fault accurately even when the time-domain features of a strongly interfered signal cannot be identified. To validate the performance of the proposed criteria, two experimental tests on a reduced-scale network composed of coaxial cables and a real power grid are performed. The fault position is located accurately by the two criteria using one-terminal measurement data. It is suggested that the two criteria can be used complementarily to enhance the fault location efficiency.

This paper studies how propagation and termination losses affect full transient-based fault location techniques. Their accuracy is discussed in terms of both location uncertainty, caused by a limited spatial resolution, and systematic errors, caused by a bias in the fault-location metrics. This last case is proven to be by far likelier when propagation losses are higher than the dissipation in line termination loads. Two different location metrics are studied, namely correlation and normalized projection, as found in the literature, with correlation proven to be unbiased, since it benefits from two location mechanisms, namely frequency and time-decay matching of a line resonances, as opposed to projection, which only relies on the former mechanism. A numerical analysis of realistic lossy overhead lines confirms theoretical predictions about biased fault location and loss of spatial resolution and the role played by the frequency content of transient data. When applied to the modal analysis of a three-phase transmission line, these results help explaining why faults are located with widely variable accuracy depending on their distance and the bandwidth of the recorded transient, confirming that wide-band transient sampling does not necessarily results in the best location accuracy.

This paper discusses the mechanisms enabling spatial resolution in fault location methods based on full transient signals, as opposed to those only using their early-time portion. This idea is found in recent travelling-wave methods (TWM) and those based on electromagnetic time reversal (EMTR). Their spatial resolution is discussed in terms of the sensitivity of a system resonances to change in the fault position and their coherence bandwidth. It is proven that using the entire transient signal it is possible to bypass the Fourier transform uncertainty principle, which limits the spatial resolution of time-domain reflectometry and standard early-time TWM. Super-resolved fault location is shown to be possible only for resonating systems, enabling high spatial resolution without relying on wide-band data. A detailed theoretical analysis for laterals and numerical results for networks and a three-phase line show that significant differences can be observed for the spatial resolution associated to each resonance, most often resulting in a loss of spatial resolution. The interaction between separate resonant structures, such as laterals in networks and coupled conductors in three-phase lines are shown to be main cause of resolution loss.

Commutation failures in high-voltage direct current (HVDC) transmission systems often occur within inverter stations, posing challenges to the safe and consistent operation of HVDC transmission projects. This paper examines data gathered from a wide-spectrum transient electromagnetic voltage monitoring apparatus. The findings uncover a notable correlation between transient AC bus voltage disturbances, stemming from faults, and the occurrence of commutation failures in HVDC transmission systems. Leveraging this correlation, we propose a commutation failure mitigation strategy for HVDC systems centered around AC bus voltage disturbances within inverter stations. Through fault validation simulations conducted across three HVDC transmission systems, our strategy demonstrates effective suppression of commutation failure incidents within HVDC transmission projects.

This paper investigates how the accuracy of fault location estimated from a transmission line's natural frequencies is affected by imperfect modeling of HVDC power-converter sta- tions. These systems include a large number of devices each with specific frequency-dependent characteristics, as filters, reactors and surge protection systems. While it is well-known that location errors may ensue from inaccurate termination models, it is not clear to what extent location accuracy is affected when neglecting one or more of these devices. Results show significant differences depending on the kind of transmission line and the reactor inductance. Including reactors is found not to completely avoid errors, proving the need to take into account the reactive behavior of the converter, which strongly varies according to the HVDC technology. A notable source of errors is level repulsion between station and line resonances, a phenomenon observed when the converter station presents self resonances, e.g., due to DC filters and stray capacitances in reactors. Significant loss of sensitivity to the fault position is found in these cases, impairing fault-location resolution. The first, or dominant, natural frequency of the line is more strongly affected by all these phenomena, suggesting that the standard choice of using the dominant resonance may not be an optimal strategy. Higher-order resonances are instead found to be more robust against inaccurate converter models, and appear to be more suitable for accurate fault location in case of uncertainties about the converter model.

This article introduces the measurement and analysis of the transient electric field (E-field) derived from the switching operation of the modular multilevel converter (MMC) and the high voltage direct current (HVdc) circuit breaker (CB) in a 200 kV converter station constructed in the Zhoushan Islands, China. It is revealed that the switching transient E-field in the converter station is a quasi-static field. Although the switching E-field pulse is a kind of electromagnetic interference to the secondary electronic circuit of the converter station, it can be used to accurately monitor the action moment of the MMC and the CB. The action moment of the MMC and the CB can be measured with an error of less than 0.005 ms based on the steep pulse front of the switching E-field pulse. This result, which is far more accurate compared to the measurement using the voltage recording system that comes with the converter station. This is of significance to the relay protection of the HVdc transmission system whose fault rapidly develops. Additionally, this method has the advantage of being noninvasive, flexible, and low cost. It has potential application value in the condition monitoring of the MMC and the HVdc CB.