Abstracts:Currently, a multitude of power electronic devices are connected to the grid, and the safe and stable operation of the grid depends on the analysis of electromagnetic transient (EMT) simulation technology. This paper proposes a state variables elimination-based EMTP-type constant admittance equivalent modeling method for power electronic converters. The method employs a three-layer architecture consisting of ‘network-nodal voltages-historical current source’. The low-order equivalent nodal voltage equation is generated by using matrix splitting and adding output equations. The proposed method is distinguished by a constant admittance matrix and the consideration of internal characteristics, which facilitates straightforward access to external circuit, low time-complexity, and uncomplicated modeling procedures in comparison with the classical node elimination method (NEM). Furthermore, it exhibits a degree of generality regarding modular and unitized electrical equipment. The accuracy of the proposed method is validated by comparison with the off-line EMT simulation and experiments. The test results demonstrate that the proposed method exhibits high accuracy and efficiency in a variety of scenarios.

Abstracts:Condition monitoring (CM) plays an important part in power asset management to sustain the high-level reliability of a power grid. Given various power asset CM techniques (CMTs), it is necessary to evaluate and select the most suitable technique that can effectively reflect equipment failure. This paper proposes a systematic method to evaluate CMTs that allows decision makers to successfully address this problem. Firstly, a multiple correspondence analysis (MCA) model is used to analyze and visualize the association among the power asset technical parameter, failure modes, and CMTs, ensuring that they can be analyzed in the same framework. Secondly, a performance score is proposed to quantitatively estimate the correspondence of each CMT in detecting failure. Thirdly, hierarchical clustering is performed to identify the most suitable CMTs for equipment with different technical parameters. Case studies are conducted with actual data in Singapore, and the results validate the effectiveness of the proposed method.

Abstracts:This letter proposes a settings-free Pseudo-Incremental Normalized (PIN) quantity-based phase selection method, which is suitable for systems with conventional and inverter-based resources (IBRs). The proposed solution process voltage and current PIN components in the same way, being flexible for applications in weak and strong terminals. The proposed method is initially evaluated by means of PSCAD simulations with the aim to compare it against five other competing solutions. Then, real-world records are used to validate the proposed method application in actual fault scenarios. In both evaluation stages, faults on lines that interconnect IBRs to synchronous generator-dominated grids are considered, allowing to assess the proposed solution under the influence of conventional generations and IBRs. The obtained results attest that the proposed phase selection method is robust, flexible and reliable, being promising for systems with conventional generations and/or IBRs.

Abstracts:This letter investigates the impact of gamma radiation on the transient performance of surge protective components under high impulse currents in the range of 0.3–2.0 kA generated by a 6 kV/3 kA combination wave generator. For the first time, the immunity of spark gaps, metal-oxide varistors, and transient voltage suppression diodes to gamma radiation is demonstrated by analyzing their residual voltage before, during, and after their exposure to a Cobalt-60 source for more than 4 minutes; samples were receiving a dose rate of 450 mGy/min. These findings (i) provide insights on test methodologies for international standards on surge protection and (ii) pave the way for implementation of surge protection schemes in highly irradiated environments, such as those encountered in the emerging power and data grids in aviation, space, nuclear, and defense industries.

Abstracts:Transformer's internal arc fault is one of its most serious faults, which might cause fire accidents. These accidents have caused widespread concern among scholars and indicated the importance of explosion-proof performance calibration. However, there is a lack of methods to estimate arc energy accurately. Within the gap length range of 5–100 mm, the current range of 1–10 kA, and the pressure range of 1–15 atm, this paper conducts 640 power-frequency arc experiments, the most numerous and well-organized experiments reported so far. An average arc voltage calculation method based on energy equivalence is proposed to avoid existing method bias and better fit the actual energy curve. Factors affecting the average arc voltage are analyzed. The relationship between the voltage and gap length approximates a linear function, and the relationship with pressure approximates a power function. An energy estimation method involving gap length and pressure is proposed. The errors of existing and proposed arc energy estimation methods are compared and reported for the first time. The proposed method dramatically reduces the average error from 43.6% to 11.5%. Repeatability experiments show that the discharge dispersion causes an average energy error of 9.1%, so the error of the proposed method is satisfactory.

Abstracts:Zone III distance protection has long operating time and its sensitivity decreases significantly in renewable energy scenarios. In this paper, novel single-ended remote backup protection is proposed based on fault location information contained in traveling wavefront. Firstly, it is demonstrated that the fault distance factor of traveling wavefront is effective in reflecting location of fault in both radial and meshed topologies. Then fault distance-operating time inverse-time characteristic is designed based on fault distance factor, realizing spontaneous sequencing of operating time between the relays at higher and lower zones. This inverse-time characteristic is only determined by location of fault and not influenced by operation mode, control strategy, fault type, fault resistance, etc. A robust algorithm is proposed to efficiently extract the fault distance factor, ensuring protection reliability. Resetting criterions are designed to re-check the existence of fault, avoiding leapfrog tripping and maloperation confronting disturbances. The setting of proposed protection is simple, without the need to update the threshold value according to the system status. Verifications have demonstrated that the proposed protection can be self-adaptive to flexible operation mode of renewable energy transmission system and different topologies. The proposed method also demonstrates high tolerance to fault resistance and noise while maintaining fast operating speed.

Abstracts:We present a test circuit for measuring the breakdown voltage characteristics of a vacuum circuit breaker after current interruption process. The test circuit combines the high current part from the synthetic test circuit as per IEC Std. 62271-101 with the so-called Rabus high voltage part. The high current part reproduces the current phase before voltage build-up occurring after zero current crossing, then the Rabus high voltage part provides voltage breakdowns constituting breakdown voltage characteristics. The high current part can be adjusted to represent the actual current conditions which influences the physical conditions of the contact system upon which the interruption process is highly dependent. To illustrate the measuring system and the measuring procedure, the measurements of the breakdown voltages are reported for a commercial 12 kV/1250 A/31.5 kA vacuum circuit breaker. The breakdown voltages are measured primarily as a function of time and then converted via a contact travel curve into the vacuum interrupter contact gap function. This allows the results to be converted back and applied to a breaker with the same characteristics of the vacuum interrupter unit operating in similar current conditions, but with different mechanical characteristics of the breaker-specific actuator than the one used in testing.

Abstracts:In recent years, the phenomenon of wideband oscillation has emerged as a significant concern for small-signal stability in modular multilevel converter (MMC) based high-voltage direct current (MMC-HVDC) systems. Sub/super-synchronous oscillations (SSOs) and high-frequency oscillations (HFOs) have been frequently reported globally, prompting the implementation of numerous control strategies aimed at mitigating these oscillatory events. However, in more complex systems, such as multi-infeed MMC-HVDC systems, there exists the potential for multi-mode oscillations, which refers to the concurrent occurrence of multiple independent oscillation components at a single electrical node. This novel oscillation issue in multi-infeed MMC-HVDC systems is still lack of relevant research. To address this issue, an analytical approach using whole-system impedance analysis alongside a parameter sensitivity index is employed to investigate multi-mode oscillation phenomena in a multi-infeed MMC-HVDC system. Furthermore, an adaptive control strategy based on fast oscillation frequency detection is proposed, which demonstrates effectiveness across various operation conditions through case studies.

Abstracts:The existing low voltage (LV) earth fault detection techniques using residual current measurements cannot be effectively applied to the multi-earthed TN-C system. When an earth fault occurs on the multi-earthed TN-C system, the fault current passes through the combined protective and neutral (PEN) conductor back to the source, resulting in a low residual current. However, unbalanced load switching also generates residual current through the same path back to the source, thus making fault discrimination very difficult. To address this problem, the four-wire multi-earthed TN-C system was analyzed by decoupling the mode 0 and the mode N of the equivalent circuit so that the current characteristics can be clearly studied. A new earth fault detection method is developed which compares the residual current deviation with the PEN conductor current deviation. The scheme uses amplitude ratio and phase angle difference between these two measurements to discriminate between earth faults and unbalanced load switching. The feasibility of the proposed method was verified by digital simulation and by physical tests in an actual LV distribution network. Compared to approaches based only on residual current, the proposed method demonstrates better sensitivity and reliability.