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This paper presents a digital distance relaying algorithm in combined transmission lines with underground power cables. When underground power cables are used as part of a transmission line, the design and setting of the protective relay will have to consider the different impedance characteristics because of the configuration characteristics of the cables. A power cable system consists of the conductor, a sheath, several kinds of joints, grounding types of such joints, cable covering protection units and grounding wires with resistance. Simulation for an actual complex transmission line with 154 kV XLPE cables was carried out to develop a correct distance relaying algorithm using modeling which was, in detail, established using EMTP and ATP Draw. This paper describes the accurate calculation algorithm of line impedance with a compensation factor at the relay point as well as a method to discriminate the fault section between both sections when a single line-to-ground fault occurs. Simulation results reveal that the accuracy of the line impedance obtained by the proposed algorithm has been increased compared with the impedance obtained using the general distance relaying algorithm.

This paper describes the strategy of a daily optimal operational schedule for cogeneration systems operating in a paper mill. The cogeneration systems consist of three generators, the several auxiliary devices which include three auxiliary boilers, two waste boilers and three sludge incinerators. One unit generates the electrical and the thermal energy using a back pressure turbine. The other two units generate both of these types of energy using an extraction condensing turbine. Auxiliary devices operate to supplement insufficient thermal energy to the thermal load with three units. The cogeneration systems have a large capacity which is able to supply enough thermal energy to the thermal load, however the electric power generated is insufficient to satisfy the electrical load. Therefore the insufficient electrical energy is supplemented by electrical energy buying from the utility. Simulation for operational schedule was carried out using Evolutionary Programming (EP). The operational cost shows that efficiency is improved by 10% compared with the past. The result reveals that the proposed modeling and the scheduling strategy can be effectively applied to cogeneration systems of another paper mills.