Ryan Tumilty

Analysis of Transient Stability Enhancement of LV-Connected Induction Microgenerators by Using Resistive-Type Fault Current Limiters

In this paper an analytical method by which the transient stability of an induction machine is maintained regardless of the fault clearance times is introduced. The method can be applied in order to improve the transient stability of a large penetration of low-voltage (LV) connected microgeneration that can be directly interfaced by single-phase induction generators within domestic premises. The analysis investigates the effectiveness of using resistive-type superconducting fault current limiters (RSFCLs) as remedial measures to prevent the microgenerators from reaching their speed limits during remote faults, and hence improving their transient stability. This will prevent unnecessary disconnection of a large penetration of LV-connected microgeneration and thus avoiding the sudden appearance of hidden loads, and unbalanced voltage conditions. The minimum required value of a resistive element of RSFCL for mitigating the transient instability phenomena of LV-connected microgeneration based on the system and connected machine parameters is determined. The analytical method has been validated by conducting informative transient studies by using detailed models of a small microwind turbine with constant mechanical output interfaced directly within residential dwellings by a single-phase induction generator, a transient model of resistive superconducting fault current limiter (RSFCL), and a typical suburban distribution network with residential loads. All the models are developed in the time-domain PSCAD/EMTDC dynamic simulation.

Analysis of a Distributed Grid-Connected Fuel Cell During Fault Conditions

The effect of a short circuit fault and a voltage sag fault on a distributed grid-connected solid oxide fuel cell (SOFC) is investigated in this paper. The fuel cell is modeled in Simulink and the performance is verified against experimental load testing data. Grid faults are simulated, and conclusions are drawn on the fuel cell response and the effects of the fault condition on internal fuel cell parameters.

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Superconducting fault-current limiters are being considered as a potential technology for restricting fault current to acceptable levels without extensive and costly network asset replacement. Such an issue currently arises primarily from the connection of a distributed generation. This paper first investigates the fault studies of an active medium-voltage distribution network with several superconducting fault-current-limiter deployment strategies and then considers their impact on circuit-breaker transient recovery voltage. These circuit-breaker characteristics at various voltage levels have been studied, and it is demonstrated that the superconducting fault-current limiter is capable of reducing both the magnitude and the rate of rise of the transient recovery voltage.

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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.

Superconducting Fault-Current Limiter in an Active Distribution Network

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.

Transient performance analysis of low voltage connected microgeneration

In a highly distributed power system (HDPS), micro renewable and low carbon technologies would make a significant contribution to the electricity supply. Further, controllable devices such as micro combined heat and power (CHP) could be used to assist in maintaining stability in addition to simply providing heat and power to dwellings. To analyse the behaviour of such a system requires the modelling of both the electrical distribution system and the coupled microgeneration devices in a realistic context. In this paper a pragmatic approach to HDPS modelling is presented: microgeneration devices are simulated using a building simulation tool to generate time-varying power output profiles, which are then replicated and processed statistically so that they can be used as boundary conditions for a load flow simulation; this is used to explore security issues such as under and over voltage, branch thermal overloading, and reverse power flow. Simulations of a section of real network are presented, featuring different penetrations of micro-renewables and micro-CHP within the ranges that are believed to be realistically possible by 2050. This analysis indicates that well-designed suburban networks are likely to be able to accommodate such levels of domestic-scale generation without problems emerging such as overloads or degradation to the quality of supply.

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

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.

Assessment of highly distributed power systems using an integrated simulation approach

This paper comes at a time when distribution network planning for distributed generation is becoming of high importance. It proposes an analysis process chosen for examining of the impact of distributed generation on the main types of distribution networks. The main objectives are to determine the impact of distributed generation on fault level, thermal constraints, statutory voltage limits, tap changer operation occurrences and losses of different networks based on the penetration level of distributed generation. The United Kingdom Generic Distribution System format has been employed for modelling the networks. Distributed generation technologies, expected to be in use by the year 2020, have been considered including combined heat and power, wind turbines and photovoltaics. Results are discussed and methods to mitigate some of these problems discussed.