The energy transition involves integrating numerous pieces of equipment that undergo frequent switching operations and face the risk of lightning strikes. Consequently, power systems are exposed to fast transient switching and lightning surges, necessitating enhanced protection solutions for power equipment. Over the past decade, viable solutions have emerged to mitigate fast transients and safeguard transformers in the form of a ring-core parallel inductor and resistor circuit (R-PIR). Although this device effectively protects medium-voltage transformers from fast transients, a precise and comprehensive model for this component is still lacking, especially considering the importance of refining the R-PIR for broader applications. This paper introduces a detailed model of the R-PIR as a protective device, validated by electromagnetic transient simulations and finite element methods, which are also confirmed by experiments. The main goals of the research work are to investigate the performance and design features of the R-PIR comprehensively and demonstrate how the designed R-PIR protects transformers against fast transients. The research work is validated by experiments conducted in a lab environment. It is concluded that designing the R-PIR within an appropriate frequency range can considerably suppress transient overvoltages to which the transformer is exposed.

Dealing with the fast-rising current of high voltage direct current (HVdc) systems during fault conditions, is one of the most challenging aspects of HVdc system protection. Fast dc circuit breakers (DCCB) have recently been employed as a promising technology and are the subject of many research studies. HVdc circuit breakers (CBs) must meet various requirements to satisfy practical and functional needs, among which fast operation, low voltage stress, and economic issues are the key factors. This article presents the procedure for designing a superconductive reactor-based DCCB (SSR-DCCB) for HVdc applications. In the proposed structure, a full-bridge power electronic configuration controls the superconducting reactor to limit the dc fault current and create a dc zero-crossing; it is connected to the HVdc line by a series transformer. After successfully suppressing the line fault current (current zero current), an ultrafast disconnector isolates the faulty line. The main advantage of the proposed HVdc CB is its ability to interrupt the dc fault current without using the solid-state main breaker and limit the magnitude of the fault current and voltage stress. The proposed SSR-DCCB is investigated in MATLAB/Simulink, and an experimental prototype setup validates the results.

The significance of battery energy storage systems (BESSs) technology has been growing rapidly, mostly due to the need for microgrid applications and the integration of renewables. Relevant to the importance of utilization of BESS in microgrids, the protection of the BESS during microgrid faults has become a concern too. The short circuit in a microgrid cause overcurrent for all of the integrated sources. BESS, as one of the sources in the microgrid, is heavily influenced by fault occurrence. The overcurrent can easily damage power electronic converter switches, battery management systems, and damage battery banks. Fault current limiters are appropriate protection devices that have been massively studied. In this article, we propose a controllable reactor fault current limiter (CRFCL) to protect the BESS against fault currents. The proposed CRFCL can control the fault current value supplied by BESS during a fault condition as a current regulator. It is realized by means of the operation of solid-state switches and series dc-reactor behavior. The main achievement of CRFCL is the protection of BESS against fault currents without delay. The simulations of the proposed structure are carried out in a MATLAB/Simulink platform, and they are confirmed and validated by experimental test results.

High local electric field intensity in transformer windings originating from transient signals is one of the reasons for transformer failures. Due to the integration of renewable energy sources into the power grids and the increased number of transients, the likelihood of transformer catastrophic failure increases accordingly. Therefore, to ensure the reliable performance of transformers and associated power networks studying their behavior during these events is required. Accordingly, there is a need for accurate modeling of transformer windings capable of simulating electromagnetic transients. Using these models, it is possible to identify frequencies that can be dangerous to the transformer windings and to study different protection schemes. This paper aims to find an accurate analytical model of transformer winding validated by experimental measurements and to study the performance of the R-L protection device during the transient phenomena. The protection device is designed based on the winding model to introduce an impedance comparable to that of the transformer winding at critical frequencies where voltage amplification in the winding is significant. This approach ensures enhanced protection against potential transformer damage to the transformer. By using this protection scheme, the high inter-turn voltage originating from transient signals may be mitigated. At the same time, it does not affect the grid's performance during normal conditions.

Future high-voltage direct-current (HVDC) networks based on voltage source converters (VSCs) will have different structures (asymmetric monopolar, bipolar, or symmetric monopolar), voltage levels, control, and protection schemes. Therefore, dc-dc converters are needed to interconnect those VSC-HVDC grids and several technical issues on their control and operational systems must be adequately addressed. A dc-dc converter based on a modular-dual active bridge (M-DAB) converter is suggested to reach a desirable interconnection of the HVDC grids and regulate power flow (PF) between them. A dynamic averaged model is proposed for the M-DAB converter and its stability is analyzed using the Lyapunov function. Moreover, a new local controller based on nonlinear control theory is proposed for the M-DAB. The new M-DAB local controller is integrated with the energy management system (EMS), by updating the PF equations, to create a complete control structure. Considering the CIGRE DCS3 HVDC test system and the studied M-DAB, static, dynamic simulation, and experimental studies are conducted and the dc-dc converter and the performance of the designed controllers and the EMS are examined and validated.

Rapid protection of modern electric networks using fault current limiters (FCLs) is often delayed and limited by the inherent controller, sensor, and power electronic unit delays. This article proposes a novel self-activated FCL (SAFCL), comprising a dc saturation winding, series ac limiter windings, and ac parallel reactor, which limits the fault current in less than 0.4 ms. Furthermore, the advantage of this SAFCL, when compared to a traditional saturated core FCL (SCFCL), is that it does not rely on any external controller, sensor, controllable solid-state switch, and battery. In the normal state, the SAFCL behaves like a saturated reactor with a very low impedance and in the fault state, cores are entered to the unsaturation region without relying on an external controller which imposes a high impedance to limit the fault, rapidly. The performance of the SAFCL is evaluated through off-line MATLAB and Maxwell ANSYS FEM simulations, and is also validated by experimental studies conducted on a scaled-down prototype.

Wind energy is the most useful type of renewable energy and wind farms are also expanding following the development of renewable energy and energy marketing. One of the types of wind farms used in the world are offshore wind farms with a length of more than 200 km, which use HVDC lines. the key concern of the offshore wind farms extensive implementation is its sensitivity in the short circuit faults. Increasing the short-circuit level and fast raising nature of the DC fault currents are some reasons for importance of protection system and choosing the appropriate protection component that is critical issue for development of offshore wind farms. Breakers are one of the main components of protection and therefore choosing a suitable breaker is vital. Breaker main features in various types of DCCB is different based on its topology characteristic. This paper aim to survey breaker main features in types of DCCBs.

Utilizing superconducting technology in fault current limiters for power grid applications is a practical solution to achieve a more modern and efficient power system. This is due to their low-loss profile, high efficiency, and ability to transmit about 5x more power in the same footprint compared to conventional counterparts. In addition, the integration of renewable energy resources into power grids makes the use of fast circuit breakers essential. However, the Transient Recovery Voltage (TRV) of fast mechanical circuit breakers stays a concern. This paper studies the TRV of a fast circuit breaker during a fault condition. Then the effect of a solid-state superconducting series reactor (SSSR) on the TRV of the circuit breaker is investigated and compared using an analytical model, simulation studies, and experimental testing. The results prove that an SSSR significantly diminishes the TRV of the fast breaker and offers an effective superconducting solution for modern power grids.

Wind energy has always been developed as one of the vital parts of modern power systems. However, by integration of wind-based generation, the level of fault current is likely to be increased which can damage the wind generators, microgrid components, and upstream grids. Consequently, utilizing viable protecting structures might preserve wind generator structures and other sections of the electric system as well. In this paper, first, the issue of the fault current of wind generators is discussed, and then well-known solution for protecting wind generators against fault current will be classified based on the comprehensive review. Next, various power electronic-based structures which are proper for protection of systems against the fault current, will be debated and ultimately the features of reviewed structures will be compared and summarized in a table for the case of wind energy generator protection.

This article presents a novel high-temperature superconductive (HTS) power flow controller and current limiter (PFCCL), which limits fault currents and manages power flow in the intended transmission line. The proposed device includes series HTS reactors, HTS controlling dc coil, recovery resistive coil, and power electronic switches, which protects the microgrid from the upstream ac grid, short-circuit faults, and it controls the power flow between a microgrid and the upstream grid. Performance of the proposed PFCCL is mathematically analyzed, utilizing MATLAB and Maxwell software, and then validated by laboratory scaled-down experimental setup. It is shown that the simulation results are in fair agreement with the developed experimental laboratory setup results.

Power systems are subjected to various types of faults as well as ferroresonance overvoltages. These results in the interruption of the normal operation of the power grid, failure of equipment, electrical fires, etc. To tackle these issues, this study proposes a dual function limiter to control the fault current and ferroresonance phenomenon in power systems. This compound device is a solid-state series transformer-based limiter that includes IGBT switches, capacitors, rectifiers, and a DC reactor. During the grid normal operation, the proposed limiter is not active and therefore is invisible and it operates in the instant of fault inception or ferroresonance overvoltage occurrences. Analytical studies in all operation modes are presented and assessments on the performance of the proposed ferroresonance and fault current limiter (FFCL) are conducted in Matlab. Simulation results confirm the reported analytical studies and FFCL's performance.

The main propose of this paper is to protect medium voltage smart grid applications from damages of the destructive fault current based on resonant type fault current limiter. Because of the series connection of a capacitor and a reactor, the Series Resonance Fault Current Limiter (SRFCL) is invisible during normal operation and shows negligible impedance in the line. During the fault, a control circuit connects a rectifier bridge to the series reactor and induces a DC voltage on it. In this instant, the series reactor is short circuited, and the series capacitor remains in the line. Thus, the impedance of the series capacitor reduces the amplitude of the fault current.