A Study on the Harmonic Resonance during Energizing Primary Restorative Transmission Systems: Korean Power System Case

In this paper, a power system restoration study following a massive or complete blackout was performed. The power system restoration process from a complete shutdown system without the operating generation and load starts with energizing primary restorative transmission systems. During this primary restoration process, unexpected over-voltage may occur due to nonlinear interaction between the unloaded transformer and the transmission system. This is known as the harmonic resonance phenomenon that may cause the burning out of a transformer or other devices. So far, harmonic resonances have been reported in some extra-high voltage systems around the world. Since the harmonic resonance originates from the nonlinear characteristics of the power system components, it is very difficult to predict the occurrence of this phenomenon. This paper reports the analyses of the harmonic resonance that can occur in the Korean power system. In addition, through calculating the required buffer load compared to the length of the line, a solution that changes the length of the restoration path impedance considering the specificity of the Korean system was presented. The various analyses of harmonic overvoltage, including methodologies that are used internationally as comparison groups, are provided based on PSCAD/EMTDC simulations.

Optimal Generation Start-Up Methodology for Power System Restoration Considering Conventional and Non-Conventional Renewable Energy Sources

Power system restoration must be accomplished as soon as possible after a blackout. In this process, available black-start (BS) units are used to provide cranking power to non-black-start (NBS) units so as to maximize the overall power system generation capacity. This procedure is known as the generation start-up problem, which is intrinsically combinatorial with complex non-linear constraints. This paper presents a new mixed integer linear programming (MILP) formulation for the generation start-up problem that integrates non-conventional renewable energy sources (NCRES) and battery energy storage systems (BESS). The main objective consists of determining an initial starting sequence for both BS and NBS units that would maximize the generation capacity of the system while meeting the non-served demand of the network. The nature of the proposed model leads to global optimal solutions, clearly outperforming heuristic and enumerative approaches, since the latter may take higher computational time while the former do not guarantee global optimal solutions. Several tests were carried out on the IEEE 39-bus test system considering BESS as well as wind and solar generation. The results showed the positive impact of NCRES in the restoration processes and evidenced the effectiveness and applicability of the proposed approach. It was found that including NCRES and BESS in the restoration process allows a reduction of 24.4% of the objective function compared to the classical restoration without these technologies.

Repairing the damage: wishful, defensive, or restorative?

Damage, physically and to the psyche is inevitable. This is whether it is caused unconsciously, through consciously malicious intent, thoughtlessness, as collateral or just through a hostile environment or the warring of internal forces. At the group or social level, the last few years have seen much damage in terms of economic recession, climate change, racial inequalities, and domestic violence. The desire to repair follows such damage. The psychoanalytic focus on reparation sees the process as an attempt by a person to repair perceived damage to another or, more precisely, to an internal image of the other—a loved other. Large groups such as organisations and societies also do damage and sometimes acknowledge this and make attempts to repair—perhaps defensively, simply to restore their own reputation, but perhaps from guilt and remorse. This article will invite readers to think about reparation in terms of either fantasied wishfulness, or defensiveness, or its possible restorative capacity. My exploration rests on the premise that damage is always to the system and that both that which damages and that which is damaged suffer. It is in system restoration that hope re-emerges.