Voltage calculation on low voltage feeders with distributed generation

Master Thesis


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University of Cape Town

The increasing levels of greenhouse gas emission and the continued depletion of fossil fuels have been the driving factors for power utilities to utilize renewable energy sources for power generation. In South Africa, a target was set in 2008 to achieve 10000 GWh of renewable generation by 2013, which includes DG on LV feeders. This has seen the increase in small scale generators, close to load centres in low voltage distribution networks such as solar PV panels in residential houses, to supplement the energy needs of consumers. This has sparked much debate over the impacts, as well as benefits, of increasing the amount of generation on these low voltage (LV) feeders. However, the power utility holds the statutory role to preserve and maintain the quality of supply of electricity and must therefore assess any impact of increasing generation on LV distribution systems. This created the need for a planning tool to assess the impact of increasing DG on LV distribution networks. There has been a lot of work carried out by researchers to assess the impact of DG on the power system, using various indicators like frequency, power losses, current, voltage etc. Keeping the voltage of a DG-integrated feeder system within the pre-defined standards has been a major challenge for power utilities today. In this report, the voltage impact of DG in LV distribution systems is examined and analysed for increasing DG penetration, particularly solar PV panels in residential households. In South Africa, the recommended method for voltage calculation in feeders is the Herman-Beta algorithm, which is used in the design of passive LV feeders. In 2011, Gaunt experimented with modelling DG as negative loads in the HB algorithm to extend the voltage calculation to include the presence of DG on LV feeders. This work identifies and develops a tool(s) to enable power utility planners to analyse the voltage impact of DG on LV feeders. The work in this study adds onto the DG modelling approach, introduced by Gaunt in 2011, to produce an algorithm for voltage calculation in active LV feeders with DG. This involves three major steps. First step involves the thorough testing of the HB algorithm, written in Matlab, for passive LV feeders and validating it against voltage calculation through Monte Carlo Simulation (MCS). The second step involves ammending and extending the HB algorithm for voltage calculation in active LV feeders with DG, testing and validation against voltage calculation through Monte Carlo Simulation (MCS). With the HB algorithm fully tested and validated, the third step involves using the algorithm for voltage analysis of active feeders with increasing DG penetration. The third and final step, analysing the voltage rise constraints of active LV feeders, involves running the HB algorithm, analytical method, in a MCS to create various scenarios on the feeder. Simulations have been performed to assess the voltage impact of increasing DG penetration on LV feeders for various test cases to mimic practical LV feeder conditions. The outcome of this study presented an application tool for the design of active LV feeders, whose output/results are summarized into implications for voltage rise mitigation and providing useful information on the DG hosting capacity of LV feeders. The recommended DG penetration limit for LV feeders in this study has been DG capacity of 30 of the actual ADMD, used to design the passive feeder. It has been shown that after this limit, the feeder should be reinforced to avoid incidents of voltage violations. In addition, the work done in this project has set a foundation upon which a variety of similar studies can be done with active LV feeders such as the effect of solar water heating and the penetration of other DG technologies such as wind.

Includes bibliographical references.