Optimal Allocation Of Distributed Renewable Energy Sources In Power Distribution Networks

In this dissertation study, various methods for optimum allocation of renewable distributed generators (DGs) in both balanced and unbalanced distribution networks have been proposed, developed, and tested. These methods were developed with an objective of maximizing several advantages of DG integration into the current distribution system infrastructure. The first method addressed the optimal sitting and sizing of DGs for minimum distribution power losses and maximum voltage profile improvement of distribution feeders. The proposed method was validated by comparing the results of a balanced distribution system with those reported in the literature. This method was then implemented in a co-simulation environment with Electric Power Research Institute\u27s (EPRI) OpenDSS program to solve a three phase optimal power flow (TOPF) problem for optimal location and sizing of multiple DGs in an unbalanced IEEE-123 node distribution network. The results from this work showed that the better loss reduction can be achieved in less computational time compared to the repeated load flow method. The second and third methods were developed with the goal of maximizing the reliability of distribution networks by optimally sitting and sizing DGs and reclosers in a distribution network. The second method focused on optimal allocation of DGs and reclosers with an objective of improving reliability indices while the third method demonstrated the cost based reliability evaluation. These methods were first verified by comparing the results obtained in a balanced network with those reported in literature and then implemented on a multi-phase unbalanced network. Results indicated that optimizing reclosers and DGs based on the reliability indices increases the total cost incurred by utilities. Likewise, when reclosers and DG were allocated to reduce the total cost, the reliability of the distribution system decreased. The fourth method was developed to reduce the total cost incurred by utilities while integrating DGs in a distribution network. Various significant issues like capital cost, operation and maintenance cost, customer service interruption cost, cost of the power purchased from fossil fuel based power plants, savings due to the reduction in distribution power losses, and savings on pollutant emissions were included in this method. Results indicated that integrating DGs to meet the projected growth in demand provides the maximum return on the investment. Additionally, during this project work an equivalent circuit model of a 1.2 kW PEM fuel cell was also developed and verified using electro impedance spectroscopy. The proposed model behaved similar to the actual fuel cell performance under similar loading conditions. Furthermore, an electrical interface between the geothermal power plant and an electric gird was also developed and simulated. The developed model successfully eliminated major issues that might cause instability in the power grid. Furthermore, a case study on the evaluation of geothermal potential has been presented

The power system and microgrid protection-a review

In recent years, power grid infrastructures have been changing from a centralized power generation model to a paradigm where the generation capability is spread over an increasing number of small power stations relying on renewable energy sources. A microgrid is a local network including renewable and non-renewable energy sources as well as distributed loads. Microgrids can be operated in both grid-connected and islanded modes to fill the gap between the significant increase in demand and storage of electricity and transmission issues. Power electronics play an important role in microgrids due to the penetration of renewable energy sources. While microgrids have many benefits for power systems, they cause many challenges, especially in protection systems. This paper presents a comprehensive review of protection systems with the penetration of microgrids in the distribution network. The expansion of a microgrid affects the coordination and protection by a change in the current direction in the distribution network. Various solutions have been suggested in the literature to resolve the microgrid protection issues. The conventional coordination of the protection system is based on the time delays between relays as the primary and backup protection. The system protection scheme has to be changed in the presence of a microgrid, so several protection schemes have been proposed to improve the protection system. Microgrids are classified into different types based on the DC/AC system, communication infrastructure, rotating synchronous machine or inverter-based distributed generation (DG), etc. Finally, we discuss the trend of future protection schemes and compare the conventional power systems

Coordination and Selectivity of Protection Devices with Reliability Assessment in Distribution Systems

This chapter provides an overview of the reliability of electricity distribution networks, and its evaluation that is linked with the protection system. In this way, the characteristics of network protection are presented, along with the peculiarities in coordination and device selectivity adjustments. For the assessment of the reliability, we have the methodology of logic-structural matrix (LSM) that integrates the constitution of the network with historical data of faults, so that with this, a model can be elaborated that can evaluate the impact of changes in the system directly on the reliability indicators

Improving reliability on distribution systems by network reconfiguration and optimal device placement.

Masters Degree. University of KwaZulu-Natal, Durban.A distribution system without reliable networks impacts production; hinders economy and affects day to day activities of its customers who demand uninterrupted supply of high quality. All power utilities try to minimize costs but simultaneously strive to provide reliable supply and achieve customer satisfaction. This research has focused on predicting and thereafter improving the South African distribution network reliability. Predictive reliability modelling ensures that utilities are better informed to make decisions which will improve supply to customers. An algorithm based on Binary Particle Swarm Optimization (BPSO) was implemented to optimize distribution network configuration as well as supplemental device placement on the system. The effects on reliability, network performance and system efficiency were considered. The methodology was applied to three distribution networks in KwaZulu-Natal, each with diverse topology, environmental exposure and causes of failure. The radial operation of distribution networks as well as the practical equipment limitations was considered when determining the optimal configuration. The failure rates and repair duration calculated unique to each network was used to model the performance of each component type. Historical performance data of the networks was used as a comparison to the key performance indicators obtained from DigSILENT PowerFactory simulations to ensure accuracy and evaluate any improvement on the system. The results of a case study display improvements in System Average Interruption Duration Index (SAIDI) of up to 20% and improvements in System Average Interruption Frequency Index (SAIFI) of up to 24% after reconfiguration. The reconfiguration also reduced the system losses in some cases. Network reconfiguration provides improved reliable supply without the need for capital investment and expenditure by the utility. The BPSO algorithm is further used to optimally place and locate switches and reclosers on the networks to achieve maximum improvement in reliability for minimal cost. The results show that the discounted future benefit of adding additional protection devices to a network is approximately R27 million over a twenty-five-year period. The maximum SAIDI improvement from adding reclosers to a network was 21%, proving that additional device placement is a cost-effective means to improve system reliability

Reliability and protection in distribution power system considering customer-based indices

A stable and reliable electric power supply system is a pre-requisite for the technological and economic growth of any nation. Nigeria's power supply has been experiencing incessant power interruptions caused by a failure in the distribution system. This paper developed a system planning approach as part of the key mitigation strategies for improved reliability and protection of the distribution network. The developed algorithm is tested using 33kV feeder supplying electricity to Kaura-Namoda, Zamfara State,  Nigeria. A customer-based reliability index was used as a tool to evaluate the reliability assessment of the feeder test system. The result showed that alternative 3 gives better results in terms of improvement of the system average interruption duration index (SAIDI), which in turn gives the minimum interrupted energy. Also, it is found that a greater number of sectionalizing switches do not give better results. It is very important to place the sectionalizing switches at a strategic location. If it is located at such points that will facilitate to sectionalize the faulty sections faster and to make the supply available to the unfaulty part of the network. Hence the utility company should apply this mitigation algorithm for system reliability improvement, depending on their needs and requirements. Thus, utilities can optimize network performance and better serve customers by adopting mitigation strategies in addressing trouble-prone areas to achieve a stable and reliable supply Keywords: distribution system; reliability; reliability indices; system performance evaluation; protection system; mitigation algorithms and sectionalizing switches&nbsp

Reverse Engineering of Short Circuit Analyses

The electrical distribution system has evolved with embedded computer systems that can better manage the electrical fault that occurred around the feeders. Such random events can affect the reliability indices of overall systems. Computerized management system for distribution operation has been improving with the advanced sensing technologies. The general research question is here to articulate is the responsiveness for utility crew to pinpoint the exact location of a fault based on the SCADA fault indicators from pole-mounted feeder remote terminal units (FRTUs). This has been a tricky question because it relies on the information received from the sensors that can conclude fault with logic\u27s of over currents. The merit of this work can benefit at large the grid reliability because of time-saving in searching the exact location of a fault. The main contribution of this thesis is to utilize the 3-phase unbalanced power flow method to incrementally search for narrowing the localization of electrical short circuits. This is known as the reversal of the typical short circuit approach where a location of the fault is presumed. The 3 topological configurations of simulation studied in this thesis exhibit the typical radial configuration of a distribution feeder have been researched based on unidirectional and bidirectional power flow simulation. The exact fault location is carried in two steps. Firstly, a bisection search algorithm has been employed. Secondly, an incremental adjustment to match the simulated currents of fault with the measurements is conducted. Finally, the sensitivity analysis of a search can be improved with the proposed algorithm that leads to matching of telemetered and calculated values. The analysis of exact fault location is carried in unidirectional and bidirectional flow of power. Distributed energy resources (DER) such as residential PV at a household level as well the wind energy changes affect the protective relaying within a feeder as well as the reconfigurability of the switching sequences. Furthermost, the bidirectionality of power flow in an unbalanced manner would also be a challenging issue to deal with the power quality in automation. Finally, the simulation results based on unidirectional and bidirectional power flow are extensively discussed along with the future scope

Reliability Studies of Distribution Systems Integrated with Energy Storage

The integration of distributed generations (DGs) - renewable DGs, in particular- into distribution networks is gradually increasing, driven by environmental concerns and technological advancements. However, the intermittency and the variability of these resources adversely affect the optimal operation and reliability of the power distribution system. Energy storage systems (ESSs) are perceived as potential solutions to address system reliability issues and to enhance renewable energy utilization. The reliability contribution of the ESS depends on the ownership of these resources, market structure, and the regulatory framework. This along with the technical characteristics and the component unavailability of ESS significantly affect the reliability value of ESS to an active distribution system. It is, therefore, necessary to develop methodologies to conduct the reliability assessment of ESS integrated modern distribution systems incorporating above-mentioned factors. This thesis presents a novel reliability model of ESS that incorporates different scenarios of ownership, market/regulatory structures, and the ESS technical and failure characteristics. A new methodology to integrate the developed ESS reliability model with the intermittent DGs and the time-dependent loads is also presented. The reliability value of ESS in distribution grid capacity enhancement, effective utilization of renewable energy, mitigations of outages, and managing the financial risk of utilities under quality regulations are quantified. The methodologies introduced in this thesis will be useful to assess the market mechanism, policy and regulatory implications regarding ESS in future distribution system planning and operation. Another important aspect of a modern distribution system is the increased reliability needs of customers, especially with the growing use of sensitive process/equipment. The financial losses of customers due to industrial process disruption or malfunction of these equipment because of short duration (voltage sag and momentary interruption) and long duration (sustained interruption) reliability events could be substantial. It is, therefore, necessary to consider these short duration reliability events in the reliability studies. This thesis introduces a novel approach for the integrated modeling of the short and long duration reliability events caused by the random failures. Furthermore, the active management of distribution systems with ESS, DG, and microgrid has the potential to mitigate different reliability events. Appropriate models are needed to explore their contribution and to assist the utilities and system planners in reliability based system upgrades. New probabilistic models are developed in this thesis to assess the role of ESS together with DG and microgrid in mitigating the adverse impact of different reliability events. The developed methodologies can easily incorporate the complex protection settings, alternate supplies configurations, and the presence of distributed energy resources/microgrids in the context of modern distribution systems. The ongoing changes in modern distribution systems are creating an enormous paradigm shift in infrastructure planning, grid operations, utility business models, and regulatory policies. In this context, the proposed methodologies and the research findings presented in this thesis should be useful to devise the appropriate market mechanisms and regulatory policies and to carry out the system upgrades considering the reliability needs of customers in modern distribution systems

Overcurrent relays coordination optimisation methods in distribution systems for microgrids: a review

Electric power networks connected with multiple distributed generations (microgrids) require adequate protection coordination. In this paper, the overcurrent relay coordination concept in distribution system has been presented with details. In this available literature, the previous works on optimisation methods utilised for the coordination of over current relays; classification has been made based on the optimisation techniques, non-standard characteristics, new constraints that have been proposed for optimal coordination and dual setting protection schemes. Then a comprehensive review has been done on optimisation techniques including the conventional methods, heuristic and hybrid methods and the relevant issues have been addressed

Fault Location, Isolation and Network Restoration as a Self-Healing function

One of the main emphasis of the smart grid is the interaction of power supply and power customer in order to provide a reliable supply of power as well as to improve the flexibility of the network. Along with this, the increased energy demand, coupled with strict regulations on the quality and reliability of supply intensifies the pressure on distribution network operators to maintain the integrity of the network in its faultless operation mode. Additionally, regardless of the huge investments already made in replacing aging infrastructure and translating “the old-fashioned grid” in a “Smart Grid” to minimize the probability for equipment failure, the chances of failure cannot be completely eliminated. In accordance, in the event of faults in the network, apart from the high penalty costs in which network operators may incur, certain safety factors must be taken into consideration for particular customers (for example, hospitals). In view of that, there is a necessity to minimize the impact on customers without supply and maintain outages times as brief as possible. Within this scenario comes the concept of self-healing grid as one of the key-technologies in the smart grid environment which is partly due to the rapid development of distribution automation. Self-healing refers to the capacity of the smart grid to restore efficiently and automatically power after an outage. Self-healing main goals comprise supply maximum load affected by the fault, take the shortest time period possible for restoration of the load, minimizing the number of switching operations and keeping the network capacity within its operating limits. This research has explored insights into the smart grid in terms of the self-healing functionality within the distribution network with main emphasis on self-healing implementation types and its applicability. Initially a detailed review of the conception of the smart grid in order to integrate the self-healing and thus fault location, isolation and service restoration capabilities was conducted. This was complemented with a detailed discussion about the electricity distribution system automatic fault management in order to create a framework around which the aim of the research is based. Finally the self-healing problem coupled with current practical implementation cases was addressed with the objective of exploring the means of improvement and evolution in the automation level in the distribution network using Fault Location Isolation and Service Restoration (FLISR) applicability as a medium