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Figure 3.24: Distribution of energy sales for 2014/2015 at eThekwini Electricity [24]
Figure 3.25: Distribution of revenue from total electricity sales at eThekwini Electricity [24]
Simulation studies are required to be able to predict the behaviour of the eThekwini Electricity distribution network with the introduction of EG. In order to carry out these simulations, a power system analysis tool is required to model the existing electrical networks thereafter various different studies can be carried out to predict the behaviour of the electrical network with the introduction of EG. There are a number of Power System simulation
PRIVATE RESIDENCES
25%
OTHER 1%
BULK 45%
PREPAID 9%
BUSINESS &
GENERAL 20%
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software packages that are currently available on the market and used by universities and utilities. For the case studies selected, various functionality was required from the selected power systems simulations software packages and reasons for the selection of the various packages are detailed below:
1. Landfill Gas to Electricity: needed a software package that support load flow and short circuit analysis. ERACS was selected since this support load flow and short circuit analysis.
2. PV Farm Case Study: needed a software package that supported RMS modelling and analysis. This was functionality was available on Digsilent Power Factory and hence Digsilent was selected for this case study.
3. Residential Rooftop PV: needed a software package that supported single phase AC and unbalance load flow analysis. Low voltage network analysis functionality is supported and available on Digsilent Power Factory.
4. Rooftop PV Projects: needed a software package that could simulate the generation output from these various rooftop PV projects. The software package that supported this was PVsyst which provided accurate site specific generation output data for each site. This package was hence used for the simulations.
Hence the three software packages that were extensively used for this research were Digsilent Power Factory, ERACS Power Systems and PVsyst simulation package.
DigSilent Power Factory Power Systems Simulations Software
Digsilent is an acronym for “Digital Simulation of Electrical Networks” and is a power systems simulation package that was designed to assist Engineers with network modeling and simulations. It is currently utlised by many utilities in Africa and around the world. [47]
Digsilent Power Factory is a powerful power systems simulation tool that offer various static and dynamic simulation fuctionality. Some of the fuctionality of Digsilent are as follows:
1. Balanced and unbalanced load flow analysis 2. Fault analysis
3. RMS stability functionality for balanced/unbalanced AC/DC systems 4. Electromagnetic Transients stability analysis
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6. Protection function analysis 7. Distribution network optimization 8. Low voltage network analysis 9. Reliability Analysis
10. .Optimal power flow (reactive power optimization)
ERACS Power System Simulation Software Package
ERACS is an electrical power systems modeling, simulation and analysis software. “It allows network design and planning engineers to simulate electrical power system networks quickly and easily judge their correct, safe and timely operation under user defined, and sometimes arduous, situations.” [48] The software package allows accurate network modelling and simulation of the electrical networks. ERACS software is utilised by eThekwini Electricity and was also utilised for the landfill gas to electricity case studies. The software package that was available supported loadflow and short ciruit analysis which was required for the study.
PVsyst PV System Modelling Package
PVsyst is a software simulation package used for modeling and simulation of PV systems.
The software offers the user three main design options.
(i) “The preliminary design option allows one to evaluate grid-connected, stand-alone and pumping systems, and use monthly values to perform a quick evaluation of system yield. For each project one has to specify the location and the system to be used. The program includes predefined values for locations of different parts of the world but also offers the option to enter the geographical coordinates, and the monthly meteorological information of new locations.” [49]
(ii) “The project design option allows one to create full-featured study and analysis of grid-connected, stand-alone, pumping, and DC-grid systems with accurately system yields computed using detailed hourly simulation data. Various different simulation variants, horizon shadings, include detailed losses, and options to add real
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components to provide economic evaluations. Upon completion of the project, reports are generated by the software.” [49]
(iii) “The tools option includes databases of meteorological information, components, solar toolboxes, and the analysis of real measured data.” [49]
The PVsyst software is used to model rooftop PV systems and the effects of rooftop inclination angles and orientation towards the sun for one of the case studies.
There are currently 105 Major Substations at eThekwini Electricity. Figure 3.26 shows that the breakdown of Major Substations within eThekwini Electricity. The two substations of interest for this study will be the 132/11 kV and the 33/11 kV substations. The distribution voltage levels at eThekwini Electricity are 11 kV, 400V and 230 V, and all of the existing EG p rojects connect at these voltage levels. Similarly, most of the proposed EG projects will connect at these voltage levels except for the case of large wind/solar farms or the 38 MW gas peaking plant.
Figure 3.26: Number of different voltage level Major Substations at eThekwini Electricity
132/11 kV Major Substation