The dc circuit breaker is an indispensable building block for dc network systems. Hybrid circuit breakers that combine mechanical and solid-state switches have more potential to be utilized in dc distribution networks because of their lower conduction losses and fast interrupt speed. The efficient energy dc interrupter with surge protection (EDISON) removes any solid-state circuit in the main current path, thereby substantially reducing the conduction losses during normal operations. However, it requires a dedicated control with fast dynamics because any false triggering of the mechanical switch or solid-state switches of the breaker would lead to a commutation failure and a potential unquenchable arc. This article proposes an FSM-based control scheme that guarantees the accurate and fast control response during a fault event. Due to this fast response requirement, a dual-core-CPU-based control architecture is applied featuring parallel taskings and negligible communication delays between the two cores. Furthermore, a control-law accelerator is employed to further reduce the latency of the program execution by 33%. The controller hardware-in-the-loop (CHIL) model of the EDISON breaker is implemented in OPAL-RT to verify the control scheme and derisk the prototype test. A fifth-order RLC network is developed to characterize the mechanical switch behavior such that the hybrid circuit model can be simulated in the CHIL solely by circuit components. Finally, the proposed control scheme is implemented and validated in a prototype test with a 3 kA interrupting current and a 60 A/ ${\mu }$ s current commutation rate.

High-temperature superconducting (HTS) direct current (dc) power cables allow high levels of power transmission and distribution at low loss and can be tailored to effectively limit fault currents. HTS Conductor on Round Core (CORC ^® ) power transmission cables offer additional benefits over other HTS cable designs, including a much higher current density and a higher degree of flexibility. These benefits make CORC ^® cables most suitable for applications in confined spaces where tight bends are required, such as onboard naval ships and in data centers. The development of CORC ^® power transmission cables for operation in pressurized helium gas is described, including their ability to act as fault current limiting cables. The 10 m long bipolar dc CORC ^® power transmission cable system is designed to operate at a current of 4000 A per pole at 50 K in pressurized helium gas. The test results at temperatures between 60 K–74 K in helium gas at a pressure of 1.7 MPa are described both during normal operation and during an overcurrent event. The results demonstrate the potential of CORC ^® cables to operate at currents exceeding 10 000 A per pole at 50 K at current densities of more than 200 A mm ⁻² , resulting in the most energy dense superconducting power transmission cable to date. The successful operation during an overcurrent event also shows the added benefits of the high level of current sharing between tapes in CORC ^® cables that allow them to be operated as FCL cables without the need to incorporate a substantial amount of stabilizer. The successful test is a major milestone towards reliable high energy density power transmission in helium gas cooled superconducting power systems based on CORC ^® cables.

Predicting the output power of wind generators is essential to improve grid flexibility, which is vulnerable to power supply variability and uncertainty. Digital twins can help predict the output of a wind turbine using a variety of environmental data generated by real-world systems. This paper dealt with the development of a physics-based output prediction model (P-bOPM) for a 10 MW floating offshore wind turbine (FOWT) for a digital twin. The wind power generator dealt with in this paper was modeled considering the NREL 5 MW standard wind turbine with a semi-submersible structure. A P-bOPM of a 10 MW FOWT for a digital twin was designed and simulated using ANSYS Twin Builder. By connecting the P-bOPM developed for the digital twin implementation with an external sensor through TCP/IP communication, it was possible to calculate the output of the wind turbine using real-time field data. As a result of evaluating the P-bOPM for various marine environments, it showed good accuracy. The digital twin equipped with the P-bOPM, which accurately reflects the variability of the offshore wind farm and can predict the output in real time, will be a great help in improving the flexibility of the power system in the future.

This article proposes a multiport modular single-stage current-source solid-state transformer (SST) for applications like photovoltaic, energy storage integration, electric vehicle fast charging, data center, etc. The 7.2 kV 50 kVA current-source SST consists of five input-series output-parallel modules, each based on 3.3 kV SiC reverse-blocking mosfet -plus-diode modules. The proposed SST has some unique features. First, compared with the voltage-source or matrix converter-based SSTs, the current-source SST has a unique advantage of single-stage isolated ac/dc or ac/ac conversion with an inductive dc link, but no medium-voltage (MV) ac experiments have been reported. This article for the first time demonstrates MV ac current-source SST up to 7.5 kV peak. Second, the multiport SST has a buffer port for active power decoupling (APD) or energy storage integration. The double-line-frequency power ripple from single-phase ac grid normally results in a large capacitor size in MV SSTs. The APD scheme is proposed in MV applications for the first time to enable a reduced dc link and the electrolytic capacitor-less SST with high reliability. Third, for a direct grid-connected converter without line-frequency transformer, insulation and protection are critical. A medium-frequency transformer design passes 55 kV basic-insulation level (BIL) and 60 kV high potential dielectrics withstand test with only 0.09% leakage inductance. Importantly, a lightning protection scheme is presented to protect the SST itself from 90 kV BIL impulse. Fourth, the proposed current-source SST topology is a modular soft-switching solid-state transformer (M-S4T) with full-range zero-voltage switching and controlled dv/dt for low electromagnetic interference. These concepts are verified in a three-port M-S4T prototype with forced oil cooling under single-module, stacked-module, steady-state, and dynamic operations.

With emerging technologies and products in power semiconductors and ultrafast mechanical switches, direct-current circuit breakers (DCCBs) have been developing rapidly. Yet the metal-oxide varistors (MOVs), being the indispensable DCCB components, are less analyzed and tested so far. Generally, MOVs in DCCBs are used to dissipate energy and limit overvoltage surges during switching events. This emerging application of MOVs calls for new design procedures and evaluation tests to ensure MOV performance under non-standard stresses and repetitive energy pulses. In this paper, online-monitored stress endurance tests are performed on MOVs that are employed in a 12 kV DCCB. Most MOVs have endured the DCCB-derived stresses for about 3500 pulses with little variation in their voltage-current characteristics, while only one fails after 1000 pulse tests and gets damaged by a shunt conductive channel. Different from conventional operating points of MOVs in their voltage-current characteristics, the MOVs in DCCB applications are found to work routinely in the temporary overvoltage (TOV) region with a decreasing TOV current over time. As these behaviors of MOVs are scarcely reported in the literature or covered by their datasheets, this study presents one of the first publicly available endurance test data that address the knowledge gaps about energy-dissipating MOVs in switchgear applications.

This study investigates the dielectric properties of various mixtures of potential gaseous cryogens containing helium (He), hydrogen (H₂), neon (Ne), and nitrogen (N₂) under extended temperature and pressure ranges for high-temperature superconducting applications. We present the results of the Boltzmann analysis on a variety of binary and ternary gas mixtures in terms of the electron energy distribution function and the coefficients that represent the electron kinetic process, including the density-reduced ionization coefficient ($\alpha /N$ ), the density-reduced attachment coefficient ($\eta /N$ ), the density-reduced effective ionization coefficient ($(\alpha -\eta )/N$ ), and the density-reduced critical electric field (${(E/N)}_{\mathit{c}\mathit{r}}$ ). The study provides insights into the important characteristics and correlations that lead to the enhanced dielectric strength of gas mixtures and predicts further enhancements in the dielectric strengths of He-H₂ mixtures by introducing the ternary mixtures of He-H₂-N₂. The study results recommend the potential ternary gas mixtures suitable for various cryogenic operating conditions and aid in the development of superconducting applications incorporating gaseous cryogens.