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  • 1.
    Bakkabulindi, Geofrey
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Planning Models for Single Wire Earth Return Power Distribution Networks2012Licentiate thesis, monograph (Other academic)
    Abstract [en]

    The high cost of grid extension to rural areas, often characterized by scattered communities with low load densities, requires the use of low cost electrification technologies to ensure economic viability. In Single Wire Earth Return (SWER) power distribution networks, the earth itself forms the current return path of the single phase system leading to significant cost savings on conductors, poles and poletop hardware compared to conventional systems. However, challenges exist in SWER with regard to earthing and safety as well as the dependence on earth conductivity to supply consumer loads.

    This work presents models for the optimal planning of SWER distribution networks. The earth return path is modeled as a conductor based on the Carson line model taking into consideration specific ground properties of the considered location. A load flow algorithm for radial SWER networks is subsequently formulated whereby both overhead line and ground voltages and currents are determined.

    First, heuristic planning models are developed based on the SWER load flow model. The objective of the heuristic models is to determine the optimum feeder configuration and overhead conductor subject to SWER load flow constraints and load growth over several time periods. Whereas the resulting solutions are good, they may not necessarily be globally optimum.

    Optimization models are then developed using mixed integer non-linear programming (MINLP) with the aim of obtaining global solutions to the SWER network planning problem. Since the MINLP formulations are limited to the accurate analysis of limited size networks, considerations and approximations for the analysis of larger networks are presented.

    The developed models are applied to a case study in Uganda to test their practical application. In addition, comparative studies are done to determine how the proposed optimization models compare with previous distribution planning models. The numerical analysis includes the impact of deterministic distributed generation on the SWER planning problem.

    Results showed consistent performance of the proposed heuristic and optimization models, which also compared well with conventional models. The optimization models gave more cost-effective solutions to the SWER planning problem than the heuristic models. However, the former models had higher computational cost than the latter. The inclusion of distributed generation allowed for cheaper network solutions to be obtained.

    The models are applicable to the planning of Single Wire Earth Return networks for isolated mini-grids, grid-extension to previously un-electrified rural areas as well as the upgrade of SWER feeders in existing installations.

    Download full text (pdf)
    Licentiate thesis - Geofrey Bakkabulindi
  • 2.
    Bakkabulindi, Geofrey
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Hesamzadeh, Mohammad R.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Amelin, Mikael
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Da Silva, I.P.
    Makerere University, Faculty of Technology.
    Planning Algorithm for Single Wire Earth Return Distribution Networks2012In: Power and Energy Society General Meeting, 2012 IEEE, 2012, p. 1-7Conference paper (Refereed)
    Abstract [en]

    Power flow in earth return distribution systems typically depends on geographical location and specific earth properties. The planning of such systems has to take into account different operational and safety constraints from conventional distribution systems. This work presents the mathematical modeling and planning of Single Wire Earth Return (SWER) power distribution networks. The SWER load flow is modeled and formulated as an optimization problem. Then by using a heuristic iterative procedure, a planning algorithm is developed for the SWER system. The developed procedure includes optimal feeder routing and overhead conductor selection for both primary and lateral feeders with load growth over several time periods. A 30 node test network extracted from a rural area in Uganda is used to test the algorithm's practical application to give reasonable and consistent results. The model presented can be used in planning SWER networks for areas which have previously not been electrified as well as determining suitable upgrades for existing SWER distribution feeders. The algorithm's mathematical modeling and simulations were done using the General Algebraic Modeling System (GAMS).

  • 3.
    Bakkabulindi, Geofrey
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Hesamzadeh, Mohammad R.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Amelin, Mikael
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Da Silva, I.P.
    Lugujjo, E.
    A Heuristic Model for Planning of Single Wire Earth Return Power Distribution Networks2011In: Proceedings of the IASTED International Conference on Power and Energy Systems and Applications, PESA 2011, 2011, p. 215-222Conference paper (Refereed)
    Abstract [en]

    The planning of distribution networks with earth return is highly dependent on the ground's electrical properties. This study incorporates a load flow algorithm for Single Wire Earth Return (SWER) networks into the planning of such systems. The earth's variable conductive properties are modelled into the load flow algorithm and the model considers load growth over different time periods. It includes optimal conductor selection for the SWER system and can also be used to forecast when an initially selected conductor will need to be upgraded. The planning procedure is based on indices derived through an iterative heuristic process that aims to minimise losses and investment costs subject to load flow constraints. A case study in Uganda is used to test the model's practical application.

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