Incorporating practice theory in sub-profile models for short term aggregated residential load forecasting

Aspirations of grid independence could be achieved by residential power systems connected only to small highly variable loads, if overall demand on the network can be accurately anticipated. Absence of the diversity found on networks with larger load cohorts or consistent industrial customers, makes such overall load profiles difficult to anticipate on even a short term basis. Here, existing forecasting techniques are employed alongside enhanced classification/clustering models in proposed methods for forecasting demand in a bottom up manner. A Markov Chain based sampling technique derived from Practice Theory of human behavior is proposed as a means of providing a forecast with low computational effort and reduced historical data requirements. The modeling approach proposed does not require seasonal adjustments or environmental data. Forecast and actual demand for a cohort of residential loads over a 5 month period are used to evaluate a number of models as well as demonstrate a significant performance improvement if utilized in an ensemble forecast

New methods for protection of future power networks incorporating high penetrations of distributed generation

Strathclyde theses - ask staff. Thesis no. : T13469Due to initiatives such as the EU (European Union) 2020 target of 20% of final energy consumption from renewable sources [1], and a target to reduce greenhouse gases from energy production by 80-95% by 2050 [2], the number of renewable generators being connected to power systems is increasing. Many modern renewable generators are inverter-interfaced [3] and many of these are being connected at the distribution level within power systems. This increase in generation at this level of the system can affect the operation of network protection, and with the continuing increase in generation, the impact on protection operation is expected to grow. In this thesis, the growing impact of inverter-interfaced generation on distribution network protection is investigated. Initially, protection problems resulting from increasing DG (Distributed Generation) penetration are investigated and the work of others in this domain is reviewed. A description of the development of an empirical model of an inverter, incorporating fault behaviour, is presented. The model is based on observations of laboratory testing and is developed to accurately model inverter fault behaviour. Three problems are subsequently considered and evaluated using simulation: protection "blinding", loss of protection coordination and sympathetic tripping. Sympathetic tripping is found to be the most 'imminent' problem and a comprehensive simulation based investigation is undertaken to evaluate the extent of sympathetic tripping for typical penetrations of distributed generation. In the latter sections of the thesis, a number of potential solutions are evaluated to ascertain their effectiveness in reducing or preventing the occurrence of protection problems such as sympathetic tripping. Firstly, it is demonstrated that sympathetic tripping can be avoided in most circumstances by modifying the settings specified in the UK Energy Networks Association's G59/2 recommendation. Secondly, the development and operation of an optimisation based technique is described - this can significantly improve the speed of protection operation and thus avoid the occurrence of sympathetic tripping; improvements in protection speed of up to 42 % are achieved with this method. Finally, a communication based blocking scheme is described which employs IP/MPLS (Internet Protocol Multiprotocol Label Switching) communication technology. The operation of this scheme is demonstrated via laboratory testing and it is shown that the selected technology may be effective when adopted within this blocking scheme. The thesis concludes with an overview of future work that is required to further advance the concepts demonstrated.Due to initiatives such as the EU (European Union) 2020 target of 20% of final energy consumption from renewable sources [1], and a target to reduce greenhouse gases from energy production by 80-95% by 2050 [2], the number of renewable generators being connected to power systems is increasing. Many modern renewable generators are inverter-interfaced [3] and many of these are being connected at the distribution level within power systems. This increase in generation at this level of the system can affect the operation of network protection, and with the continuing increase in generation, the impact on protection operation is expected to grow. In this thesis, the growing impact of inverter-interfaced generation on distribution network protection is investigated. Initially, protection problems resulting from increasing DG (Distributed Generation) penetration are investigated and the work of others in this domain is reviewed. A description of the development of an empirical model of an inverter, incorporating fault behaviour, is presented. The model is based on observations of laboratory testing and is developed to accurately model inverter fault behaviour. Three problems are subsequently considered and evaluated using simulation: protection "blinding", loss of protection coordination and sympathetic tripping. Sympathetic tripping is found to be the most 'imminent' problem and a comprehensive simulation based investigation is undertaken to evaluate the extent of sympathetic tripping for typical penetrations of distributed generation. In the latter sections of the thesis, a number of potential solutions are evaluated to ascertain their effectiveness in reducing or preventing the occurrence of protection problems such as sympathetic tripping. Firstly, it is demonstrated that sympathetic tripping can be avoided in most circumstances by modifying the settings specified in the UK Energy Networks Association's G59/2 recommendation. Secondly, the development and operation of an optimisation based technique is described - this can significantly improve the speed of protection operation and thus avoid the occurrence of sympathetic tripping; improvements in protection speed of up to 42 % are achieved with this method. Finally, a communication based blocking scheme is described which employs IP/MPLS (Internet Protocol Multiprotocol Label Switching) communication technology. The operation of this scheme is demonstrated via laboratory testing and it is shown that the selected technology may be effective when adopted within this blocking scheme. The thesis concludes with an overview of future work that is required to further advance the concepts demonstrated

Investigation of the sympathetic tripping problem in power systems with large penetrations of distributed generation

This study contains an investigation into sympathetic tripping – the undesirable disconnection of distributed generators (DGs) (in accordance with the recently-introduced G83/2 under voltage protection) when a network fault occurs in the vicinity of the DG and is not cleared quickly enough by the network protection (i.e. before the DG's under voltage protection operates). An evaluation of the severity of and proposal of solutions to the problem of sympathetic tripping on a typical UK distribution power network is presented. An inverter model (as the majority of DGs will be inverter-interfaced) that characterises the fault response of the inverter and its associated protection functions has been developed for use in simulation through exhaustive laboratory testing of a commercially-available 3 kW inverter for DG application; the observed responses have been modelled and incorporated in a power system simulation package. It is shown, when using presently-adopted DG interface and network protection settings, that the risk of sympathetic tripping is high in several future scenarios. To mitigate this risk, the impact of modifying network protection settings is evaluated. This study has two key findings – determination of the conditions at which the risk of sympathetic tripping is high and evaluation of a technique to mitigate this risk