Bruno Jorge de Oliveira e Sousa

Block-Layer Reliability Method for Distribution Systems Under Various Operating Scenarios

This paper formulates a block-layer method for the reliability assessment of distribution systems. The characteristics of the method include: 1) identifying the impact of distribution component reliability on the system and load points using a block-layer structured assessment; 2) incorporating time-dependent failure parameters; and 3) taking account of the topological, seasonal, and meteorological features of the distribution systems under analysis. The proposed method first identifies the three critical parts of the distribution system: main supply, feeder, and secondary substation. It can also include reserve connections and distributed generation. Second, the method frames these parts into the layered structure, each corresponding to the zone of total load curtailment. To verify this reliability technique, this paper simulates distribution feeders assembled in a number of topologies and compares them with the state sampling technique. Data provided by the local utility company are processed to model the equipment and load for the base year. The results show that the proposed method can provide a wide range of partial and system indices. These values assist in the identification of parts of the distribution system and scenarios with low reliability and to determine possible remedial actions.

The Importance of Realistic Load Modeling in Power System Harmonic Respnance Analysis

Parallel resonances in electrical power systems can considerably increase levels of harmonic voltages, which may lead to a component breakdown. Major capacitive network components, such as shunt capacitors, can significantly change the network harmonic impedance. It is therefore common to perform a harmonic load flow analysis before the installation of these devices. Due to the difficulty of accurate modeling, system loads are often ignored in such assessments. However, this approach can lead to very pessimistic results, possibly leading to unnecessary investments in filtering solutions. This paper presents the results of a harmonic load flow analysis that was performed during the planning of new capacitors in the 110-kV subtransmission network of Helsinki. Different harmonic load models were employed. The results indicate that because of load damping in the network, it is not necessary to have additional harmonic limiting devices with the capacitors.

Influence of voltage sags and outage costs on realistic radial and backed-up 20-kV rural and urban networks

This research investigates the cost burden of voltage sags and outages of two feeders in typical rural and urban environments in Finland, and compares the effect of different voltage sags on their adjacent feeders. The two tested feeders were each sampled from two 20-kV distribution networks generated by a Network Topology Optimizing Algorithm (NTOA) based on data from a rural area in Western Finland and from the metropolitan region of Helsinki. This study divides the base year into four seasons and considers load data, features and constraints intrinsic to the local scenarios. As inputs to the cost assessment, the reliability technique estimates important reliability indices at each substation. The residual voltages during contingencies, analytically obtained, define the voltage sag rates at several points of the feeders under focus. As main conclusions, voltage sag costs in the simulated feeders are significantly smaller than the outage costs, but voltage sags originating in certain zones of these feeders directly affect voltage levels in other adjacent feeders and upstream equipment, thus propagating the economic burden to other parts of this network.

Evaluation of fault current limitation techniques in urban meshed 110-kV subtransmission networks

In the municipality of Helsinki, plans to expand its subtransmission network in the next few years predict excessive high short-circuit levels in numerous substations. The existing network embodies overhead lines (OHL) and underground cables (UGC), in many occasions assembled in parallel, as well as combined heat and power (CHP) facilities. Furthermore, it is characterized by meshed topology, which ensures system flexibility and improved reliability; however, this configuration favors propagation of fault currents and voltage sags across the grid. To minimize damage from these, the present study investigates prospective fault current limitation techniques, including the superconducting fault current limiter (SFCL), regarding the features of the Helsinki subtransmission network. This paper inspects the optimal location of these solutions and performs economic assessment. Moreover, it examines the benefits of the employed techniques, assesses whether they achieve the desired operational performance, and quantifies total costs, accrediting load growth for a 40-year period.