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Segmentation of large AC systems through DC links introduces a new concept that utilizes the advantages of direct current transmission to improve network reliability and increase power transfer capacity. Technical literature argues that the segmentation of the AC network and the introduction of DC links at these systems connection points bring benefits to system operation, once contingencies generated on one side of the DC connection point would not be reflected on the other side of DC connection, thereby reducing the likelihood of cascading shutdowns and blackouts due to load restraint on transmission lines and transformers. Amidst this scenario, this paper presents a study of the main topics regarding the use of this new network segmentation philosophy, bringing a practical point of view for the use of this concept at the electrical power system planning. The effect of DC segmentation before a contingency that would initiate major outages in an adapted electrical system model IEEE-14 bus is studied and simulations have been performed with test HVAC systems and segmented by HVDC link. The results have been compared, principally in relation to the voltage bus, reactive power generation, system losses and power flow at the lines, and demonstrated that this new concept improved the grid reliability.

Abstract. The growing demand for electric power together with the environmental agencies pressure for decreasing polluting gases emission are the main causes of the big expansion that Distributed Generation systems have been undergoing lately. This kind of electric generation system allows to produce parts of the electricity power nearby the costumers making energy costs cheaper for final consumer and improving the share of clean sources on the energy matrix. Despite Germany's great experience with photovoltaic plants, Distributed Generation systems are not well widespread around the world. Most governmental regulations about the theme are recent and sometimes do not cover all the specificities, so it has been continuously rewritten. Although Brazilian market has a small concentration of sources connected to the distribution grids, the annual relative growth is significant. High concentration of sources nearby the costumers may cause problems in the operation and in the stability of electric quantities. Some of these problems are voltage rises, harmonics and general damages to electrical equipment. This paper presents the voltage rise effect in distribution grids with high concentration of generators; it also suggests mitigation techniques for this outcome. It becomes clear that is possible to reverse power flow without voltage rise beyond legal limits.

The growing demand for electric power together with the environmental agencies pressure for decreasing polluting gases emission are the main causes of the big expansion that Distributed Generation systems have been undergoing lately. This kind of electric generation system allows to produce parts of the electricity power nearby the costumers making energy costs cheaper for final consumer and improving the share of clean sources on the energy matrix. Despite Germany's great experience with photovoltaic plants, Distributed Generation systems are not well widespread around the world. Most governmental regulations about the theme are recent and sometimes do not cover all the specificities, so it has been continuously rewritten. Although Brazilian market has a small concentration of sources connected to the distribution grids, the annual relative growth is significant. High concentration of sources nearby the costumers may cause problems in the operation and in the stability of electric quantities. Some of these problems are voltage rises, harmonics and general damages to electrical equipment. This paper presents the voltage rise effect in distribution grids with high concentration of generators; it also suggests mitigation techniques for this outcome. It becomes clear that is possible to reverse power flow without voltage rise beyond legal limits.

With the objective to reduce the environmental pollution, alternative initiatives have favored the evolution of the electric vehicle (EV). As the electric vehicle depends solely on battery, the grid electric power is need for charging it. This new electric load can cause concern due to the impact of consume on power system. The behavior of main electric parameters is analyzed during the recharge of EV considering an actual condition of diary charge. In sequence, the data of these electric parameters obtained during EV charging were included on residential consumer energy from Brazil. The results contribute to the understanding of the recharge of EV in different time of the day which can affect the curve of residential consumer energy and consequently will affect in different way on Power System.

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The Conservation Voltage Reduction (CVR) is a technique that aims to achieve the decrease of power consumption as a result of voltage reduction. The customer is supplied with the lowest possible voltage level compatible with the stipulated level by the regulatory agency. International Standards ANSI C84.1-2006 and IEEE std 1250-1995 specify the range of supply voltage to electronics equipment from 0.9 to 1.05 pu of nominal voltage. To analyse the CVR effect in distribution systems with different load characteristics (residential, commercial, industrial or a combination of these), mathematical load models are used. Typically, these equipment/load models are used to analyse load aggregation without any consideration of its nonlinearity characteristics. Aiming to analyse the nonlinear characteristics and its consequences, this paper presents a discussion of the neglected variables as well as the results of a set of measurements of nonlinear loads. Different mathematical models are applied to obtain them for each load. Using these models the load aggregation is evaluated. It is presented that although the models show adequate results for individual loads, the same does not occur for aggregated models if the harmonic contribution is not considered. Consequently, to apply the load model in CVR it is necessary to consider the harmonics presence and the model has to be done using only the fundamental frequency data. The discussion about the causes is done and the models are compared with the measurements.

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