Supporting transient stability in future highly distributed power systems

Incorporating a substantial volume of microgeneration (consumer-led rather than centrally planed) within a system that is not designed for such a paradigm could lead to conflicts in the operating strategies of the new and existing centralised generation technologies. So it becomes vital for such substantial amounts of microgeneration among other decentralised resources to be controlled in the way that the aggregated response will support the wider system. In addition, the characteristic behaviour of such populations requires to be understood under different system conditions to ascertain measures of risk and resilience. Therefore, this paper provides two main contributions: firstly, conceptual control for a system incorporating a high penetration of microgeneration and dynamic load, termed a Highly Distributed Power System (HDPS), is proposed. Secondly, a technical solution that can support enhanced transient stability in such a system is evaluated and demonstrated

A dynamic modelling environment for the evaluation of wide area protection systems

This paper introduces the concept of dynamic modelling for wide area and adaptive power system protection. Although not limited to these types of protection schemes, these were chosen due to their potential role in solving a multitude of protection challenges facing future power systems. The dynamic modelling will be implemented using a bespoke simulation environment. This tool allows for a fully integrated testing methodology which enables the validation of protection solutions prior to their operational deployment. Furthermore the paper suggests a distributed protection architecture, which when applied to existing and future protection schemes, has the potential to enhance their functionality and avoid mal-operation given that safety and reliability of power systems are paramount. This architecture also provides a means to better understand the underlying dynamics of the aforementioned protection schemes and will be rigorously validated using the modelling environment

Modelling the impact of micro generation on the electrical distribution system

In the UK and elsewhere there is considerable debate as to the future form of the electricity distribution system. The coming years will see a rise in the amount of micro-generation connected to the network at low voltages and the emergence of highly-distributed power systems (HDPS). However, there is considerable uncertainty as to the impact that this micro-generation will have on the quality of power supplied to our homes or to the stability of the electricity system as a whole. To address these engineering challenges the UK Engineering and Physical Sciences Research Council (EPSRC) is funding a three year research programme featuring a multi-disciplinary team from a variety of UK Universities: Supergen HDPS. This paper documents one piece of work emerging from the consortium, where a multi-tool approach is used to analyse the impact of micro-generation on the electricity system. This used a building simulation tool to produce electrical generation profiles for domestic cogeneration device models. These, along with profiles produced for other micro-generation technology models and electrical load profiles are then replicated and aggregated using a customised statistical approach. The profiles were then used as boundary conditions for a set of electrical load flow simulations on a model of a section of real network, where the number of microgenerators was varied according to different scenarios for the future of the UK electricity grid. The results indicate that a significant number of micro-generation devices can be accommodated before any power quality problems arise, however this is dependent upon maintaining a robust central grid

Electricity network scenarios for 2020

This report presents a set of scenarios for the development of the electricity supply industry in Great Britain in the years to 2020. These scenarios illustrate the varied sets of background circumstances which may influence the industry over the coming years – including political and regulatory factors, the strength of the economy and the level to which environmentally-driven restrictions and opportunities influence policy and investment decisions. Previous work by the authors (Elders et al, 2006) has resulted in a set of six scenarios illustrating possible developments in the electricity industry in the period up to 2050. While such scenarios are valuable in gauging the long-term direction of the electricity industry and its economic and environmental consequences, shorter-range scenarios are useful in assessing the steps necessary to achieve these long-range destinations, and to determine their relationship to current trends, policies and targets. In this chapter, a set of medium-range scenarios focused on the year 2020 is developed and described. These scenarios are designed to be consistent both with the current state of the electricity supply industry in Great Britain, and with the achievement of the ultimate electricity generation, supply and utilisation infrastructure and patterns described in each of the 2050 scenarios. The consequences of these scenarios in terms of the emissions of carbon dioxide are evaluated and compared with other predictions. The SuperGen 2020 scenarios described in this report were developed as a collaborative effort between the SuperGen project team and the ITI-Energy Networks Project team both based at the University of Strathclyde

A study of adaptive protection methods for future electricity distribution systems

The traditional transmission centric approach to generation connection using large-scale thermal units is evolving as the electricity supply industry and end users both move to play their part in tackling climate change. Government targets and financial incentive mechanisms have created a generation portfolio that is becoming more diverse as both large and small-scale distributed generation projects are commissioned. The net result of these events is that generation now appears across all voltage levels and is a trend that is almost certainly set to continue. Moreover, the manner in which networks are operated is also changing to become more flexible with novel management intended to facilitate the dispersed connection of generation, whilst at the same time improving the quality of supply for end users. As a consequence of the foregoing changes, new challenges emerge with regard to guaranteeing that the performance of power system protection is not degraded. This thesis documents research that has considered the myriad of issues arising throughout distribution networks. The concept of adaptive protection has been explored as a solution to many of these issues as a means of ensuring that protection better reflects the current state of the primary power system. Although adaptive protection has been a theoretical possibility for some time it has not generally been applied in practice. The emerging drivers that could change this have been considered along with the challenges of its application. It was concluded from this work that the concept and structure for adapting protection needs to be examined in abstraction from the underlying low level protection algorithms. A layered architecture has been proposed that helps to structure process of adaptation, define key functionality and ultimately clarify how it could be practically realised using currently available substation protection and automation equipment. To demonstrate the application of the architecture two examples have been used that cover both low and high voltage networks. The first considers a low voltage microgrid and the difficulties resulting from inverter interfaced microgeneration. As a second example, the problem of intentionally islanding an area of high voltage network is considered. Taken together, these two examples cover a range of future scenarios that could emerge within so called smart grids.The traditional transmission centric approach to generation connection using large-scale thermal units is evolving as the electricity supply industry and end users both move to play their part in tackling climate change. Government targets and financial incentive mechanisms have created a generation portfolio that is becoming more diverse as both large and small-scale distributed generation projects are commissioned. The net result of these events is that generation now appears across all voltage levels and is a trend that is almost certainly set to continue. Moreover, the manner in which networks are operated is also changing to become more flexible with novel management intended to facilitate the dispersed connection of generation, whilst at the same time improving the quality of supply for end users. As a consequence of the foregoing changes, new challenges emerge with regard to guaranteeing that the performance of power system protection is not degraded. This thesis documents research that has considered the myriad of issues arising throughout distribution networks. The concept of adaptive protection has been explored as a solution to many of these issues as a means of ensuring that protection better reflects the current state of the primary power system. Although adaptive protection has been a theoretical possibility for some time it has not generally been applied in practice. The emerging drivers that could change this have been considered along with the challenges of its application. It was concluded from this work that the concept and structure for adapting protection needs to be examined in abstraction from the underlying low level protection algorithms. A layered architecture has been proposed that helps to structure process of adaptation, define key functionality and ultimately clarify how it could be practically realised using currently available substation protection and automation equipment. To demonstrate the application of the architecture two examples have been used that cover both low and high voltage networks. The first considers a low voltage microgrid and the difficulties resulting from inverter interfaced microgeneration. As a second example, the problem of intentionally islanding an area of high voltage network is considered. Taken together, these two examples cover a range of future scenarios that could emerge within so called smart grids

Transient performance analysis of low voltage connected microgeneration

The growing awareness of the environmental impacts of large-scale thermal generating units has stimulated interest in microgeneration that is installed within domestic or commercial premises. This paper investigates the transient response to be expected from a range of microgeneration units that could typically be connected. The paper examines the impact of fault locations, typical fault clearance times and generator/prime mover technologies on the ability of microgenerators to maintain stability when subject to disturbances during and after clearing of both local low and remote medium voltage faults. The paper also presents the study of the step voltage changes occurring due to the simultaneous reconnection of a large number of microgenerators within a small area of the network. Two types of technologies are considered in this paper: a small diesel engine driving a three-phase synchronous machine connected within commercial premises; and a small microwind turbine interfaced directly within a residential dwelling by a single-phase induction generator

Transient performance analysis of single-phase induction generators for microgeneration applications

This paper presents studies of a single-phase induction machine driven by a micro wind turbine connected to an LV distribution system within a residential dwelling. The transient associated with grid connection and both local and electrically remote network faults are presented. Based on these studies conclusions will be drawn regarding the network impacts of microgenerators using single-phase induction generators and, conversely, the impact of network secondary systems such as protection (e.g. typical fault clearance times) on the behaviour of these generators, and also the threshold values of the machine speed and its retained terminal voltage when the system experiences a remote fault on the MV system are defined. The principle contribution of this paper is to highlight stability issues associated with such small scale generators, and to propose some remedial measures by which the stable operation of such generators may be improved

Improving the transient performance of a high penetration of LV connected microgeneration

This paper widens the knowledge about the microgeneration transient response under faulted conditions. The paper provides the following significant contributions: Firstly, a range of microgeneration transient models have been developed in PSCAD/EMTDC and tested on a typical distribution network. Two types of technologies are considered: a small diesel engine driving a three-phase synchronous machine connected within commercial premises; and a small microwind turbine interfaced directly within residential dwellings by a single-phase induction generator. Secondly, a valuable insight into the transient behavioral of this range of technologies during and after the clearing of remote faults at a medium voltage (MV) distribution system is provided, and their resilience levels are quantified. Thirdly, for reliable microgeneration operating in parallel with the distribution networks, the paper includes a discussion on some of remedial measures by which the transient stability of a large penetration of microgeneration may be improved. Also in this paper the inclusion of resistive superconducting fault current limiters into medium voltage distribution systems has been proposed as one of the practical solutions that can enhance the transient performance of large numbers of low voltage connected microgeneration. The effectiveness of fault current limiters on the grid-connected microgeneration transient stability enhancement has also been evaluated