The DC currents in a power system maybe caused by Geomagnetic Disturbances (GMDs) that are the result of solar storms and high-altitude nuclear detonations. The increased inverter-based generation is also contributing to small DC injection into the power systems. The resultant DC currents could have serious consequences for the power systems as they may drive the power transformers into saturation, cause transformer internal heating, cause large draw of reactive power and miss-operation of protective relays. This paper proposes a novel power electronics-based DC mitigation approach that involves a transformerless series active filter integrated between the neutral point and earth ground of power transformers serving multiple purposes. The first objective is to surpass the effect of DC injection, the second goal is voltage regulation, the third is to provide harmonic isolation or impedance balancing. The proposed device is currently being developed on a 7.2kV/240V single-phase transformer, however, the solution is also relevant for 24 to 500 kV networks. The system circuitry, operation and control are implemented and verified for this paper in a Controller Hardware-in-the-Loop (C-HIL) test setup using a Typhoon HIL 402 simulator. Results indicate that our approach is a promising alternative to traditional neutral capacitor blocking strategies.

Geomagnetic Disturbances (GMDs) are the result of solar storms or a high-altitude nuclear detonation. On the power systems, they might lead to the flow of quasi-DC currents referred as Geomagnetically Induced Currents (GICs). These currents cause the AC current offset that may drive the power transformers into saturation. This leads to large draw of reactive power, causes transformer internal heating and increased noise level, damage to shunt capacitors, harmonic filters and maloperation of power system protection equipment. This paper reviews the state-of-the-art of the GIC mitigation and elimination strategies and their respective limitations. It also introduces converter-based strategies as a new avenue of power system protection against GICs by presenting novel strategies that involve the integration of the proposed schemes between the neutral and ground of power transformers. One of the proposed schemes is a contribution to the approaches solely focused towards GIC mitigation, whereas, the other provides a variety of grid-support functions in addition to GIC elimination. The simulations performed in a Controller Hardware-in-the-Loop (C-HIL) environment verify the proposed schemes as a promising alternative to the current GIC mitigation approaches.

The DC in a power network might be caused by geomagnetic disturbances (GMDs) that result from either a geomagnetic storm or a high-altitude nuclear detonation. The augmenting trend of inverter-based resources is also acting as a source of small DC injection into the power systems. As the resultant DC could lead towards a possible power system failure, a myriad of neutral blocking devices (NBDs) have been proposed, where, these devices are installed between the neutral and ground of wye-grounded transformers. However, the electrical safety assessment of these devices is critical prior to adding them to the grid as they might raise serious concerns both for the power equipment and the power system maintenance staff. This work is the first effort towards hazard identification and quantitative risk assessment associated with NBDs. It proposes a risk management framework for augmented electrical safety pertinent to these devices. Later, it analyses the proposed neutral blocking strategies and highlights the associated risks to the operational safety of these installations, particularly concerning EMP attacks, cyber threats and equipment malfunction. Finally, an ideal NBD operational design is also proposed incorporating a variety of risk reduction measure (RRMs) to avoid any hazardous situation arising from such installations. This work could provide a guideline for the electric utilities and academic researchers to consider these safety implications prior to proposing or installing these devices.

Power Hardware-In-the-Loop (PHIL) testing is a powerful approach that combines the flexibility of numerical simulations with the high fidelity of hardware tests to allow experimental validation of electrical equipment in a close-to-reality laboratory environment. This is enabled by using specially designed software and hardware that serve as an interface between the modeled environment and the equipment under test. Using PHIL for testing and validation can help significantly reduce time-to-market for novel energy solutions by both reducing the number of design/prototyping iterations, which in turn reduces the development costs, and the need for timely and costly field tests later during the system validation stage. The PHIL as a technology has been studied over the last 20 years, focusing mostly on the software/hardware interfaces and on system stability challenges. However, there has not been a consensus yet on how a PHIL system should be designed, validated and operated to maximize its benefits. The present work provides answers to these questions. Starting from the existing research experience and use cases, the present paper introduces practical guidelines for PHIL modeling, design, laboratory implementation and validation, and it identifies a few remaining open topics that need to be addressed to enable wider adoption of PHIL for testing and validation of electrical equipment in industrial environments.

Building-level electrical distribution systems comprise a myriad of current-carrying equipment, conversion devices, and protection devices that deliver power from the utility or local distributed energy resources to end-use building loads. Electric power has traditionally been generated, transmitted, and distributed in alternating current (AC). However, the last decade has seen a significant increase in the integration of native direct current (DC) equipment that has elevated the importance of DC distribution systems. Numerous studies have comparatively examined the performance of various electrical distribution systems in buildings but have failed to achieve uniform conclusions, primarily because of a lack of consistent and analogous performance evaluation methods. This paper aims to fill this gap by providing a standard set of metrics and measurement boundaries to consistently evaluate the performance of AC, DC, or hybrid AC/DC electrical distribution systems. The efficacy of the proposed approach is evaluated on a representative medium-sized commercial office building model with AC distribution and an equivalent hybrid AC/DC and DC distribution model, wherein the AC distribution model is concluded to be the most efficient. The simulation results show variation in computed metrics with different selected boundaries that verify the effectiveness of the proposed approach in ensuring consistent computation of the performance of building-level electrical distribution systems. This paper provides an initial set of guidelines for building energy system stakeholders to adopt appropriate solutions, thus leading to more efficient energy systems.