Search

The electrification of heat and transport, and the increased penetration of distributed generation (DG), have the potential to significantly impact thermal constraints, voltage saturation and fault levels of Northern Ireland Electricity Networks (NIEN) ‘last mile’ low-voltage (LV) networks. To avoid/defer expensive reinforcement to address such challenges, NIEN in collaboration with WSP will trial active network management (ANM) scheme to maximise the utilisation of existing assets with flexibility that can benefit from sharing spare capacity between neighbouring LV networks. To do so, an approach to change the configuration and operation of stressed LV networks from ‘radial’ to ‘meshed’ will be considered. However, such a radical change in the network configuration will require LV protection strategies to be re-evaluated. In response to this, this study provides the following contributions: (1) presenting an overview of the NIEN ANM scheme, (2) investigation of the potential impact on the LV protection when the NIEN ANM is implemented (through modelling and simulation studies under different short-circuit fault conditions), and (3) providing recommendations on LV protection arrangements that are required to deliver reliable protection operation with a good level of selectivity for enabling resilient operation of the ANM scheme.

The increasing electrification of transport and heat will place increasing demand on low voltage (LV) networks with the potential to overload medium voltage (MV)/LV transformers and LV cables. Deployment of a solid-state transformer (SST) at MV/LV substations and using LV direct current (LVDC) distribution systems offer great potential to address such challenges. However, the SST deployment in addition to the introduction of LVDC will fundamentally change LV fault behaviour and protection requirements due to the limited short-circuit capabilities of such technologies. The SST will deliver limited fault currents, making current-based protection (widely used in LV networks) less reliable. Therefore, this study presents an advanced communication-less protection scheme which can effectively detect and locate DC faults even with reduced fault levels. The developed protection scheme overcomes the selectivity limitations in LVDC voltage-based protection solutions by using a combination of DC voltage magnitude, voltage concavity (sign of d 2 v /d t 2 ) and the sign of the rate of change of current (d i /d t ) regardless of the current magnitudes. The credibility of the developed protection algorithm is tested against different fault scenarios applied on an active LVDC network model built in PSCAD/EMTDC. Noise signals have been included in the simulation to appraise the resilience of the developed scheme.

Low Voltage Direct Current (LVDC) distribution systems have recently been considered as an alternative approach to electrical system infrastructure as they provide the additional flexibility and controllability required to facilitate the integration of more low carbon technologies (LCTs). However, DC protection systems and, more specifically high accuracy DC fault location, have been recognised as a key challenge to facilitating post-fault network maintenance. Most of the existing fault location techniques rely on current derivative or communications-based methods that are either very sensitive to noise, or require a high level of data synchronisation. Fault energy has been recognized as a reliable indicator of more accurate fault location estimations. Therefore, this paper develops a mathematical model for describing fault energy during the transient period of DC faults. The method subsequently proposes a new fault let-through energy based DC fault location working strategy to facilitate post-fault network maintenance. The proposed method does not require data synchronisation regardless of the voltage, current, and the size of the converters connected to the LVDC feeder. The capabilities of the proposed fault location strategy are validated against different faults applied on an LVDC test network in PSCAD/EMTDC and shown to be more reliable and accurate than existing methods.

This article presents a new method for locating faults along feeders in a direct current (dc) microgrid using a multiple capacitive earthing scheme. During fault conditions, capacitors within the earthing scheme are charging by transient currents that correlate with the fault distance and resistance. Therefore, by assessing the response of the capacitive earthing scheme during the fault, the distance to fault is estimated. The proposed method utilizes instantaneous current and voltage measurements (obtained from the feeder terminals and earthing capacitors) applied to an analytical mathematical model of the faulted feeder. The proposed method has been found to accurately estimate the fault position along the faulted feeder, and the systematic evaluation has been carried out to further scrutinize its performance under different loading scenarios and highly resistive faults. In addition, the performance and practical feasibility of the proposed method have been experimentally validated by developing a low-voltage laboratory prototype and testing it under a series of test conditions.

This paper presents a new fault location method using capacitive earthing charge current combined with moving average and Savitzky-Golay filters. Locating a DC fault in a DC microgrid can be challenging due to reduced fault current magnitudes, resulting either from high resistive faults, or during the transition between grid-connected and islanded modes. The capacitive earthing method is proposed for earthing DC systems to avoid the corrosion of earthed metallic surfaces. Under different fault conditions and at different locations, the capacitive earthing with the earth path, charges a transient current with a peak value that depends on the initial voltage of the capacitor and the fault loop between the capacitor and the fault point. Therefore, this paper utilises earth capacitor pre-fault voltages, transient current peak and the derivative current of the capacitive earthing to estimate the total inductance of the fault loop. This in turn can be used to determine the location of DC faults. This paper also quantifies the impact that resistive faults have on the accuracy of the method, especially when the resistance of the fault dominates the total fault loop. The ability to distinguish between downstream and upstream faults with respect to the earthing point location also adds significant value to the proposed method. The proposed fault location technique is tested against pole-to-earth fault at different locations using Matlab-Simulink.

This paper provides an assessment of passive islanding detection methods in DC microgrids. In order to analyse the response of a DC microgrid to an islanding event, DC voltage and current signatures are captured locally at the terminals of Distributed Energy Resources (DERs). Further analysis on DC voltage and current measurements is carried out to derive the Rate of Change of Voltage (ROCOV) and the Rate of Change of Current (ROCOC), to distinguish between genuine islanding events and other disturbances. A detailed DC microgrid has been developed in MATLAB/Simulink to analyse the response of the DERs within a DC microgrid during intentional or unintentional islanding events. The results show that these approaches cannot be used to classify and characterise between islanding and non-islanding events caused by high resistive faults for DC microgrids, as the response of the DERs are dependent on the technology and associated control systems,which influences post event analysis in distinguishing between events.

DC microgrid technology has become one of key smart grid research topics in recent years. In comparison to AC microgrids, DC microgrids are more manageable to operate in grid-connected and islanded modes, and also offering improved efficiency and better controllability. Services, such as voltages and AC system frequency support can also be potentially provided by optimally controlling the DC microgrids converter interfaces and their local distributed energy resources. These will require a good understanding of the dynamic interactions between the DC microgrid and the host AC system, and implementation of the appropriate control strategies. This paper investigates the dynamic resilience of a DC microgrid connected to an AC system under different frequency and voltage disturbances. A decentralised droop control strategy within the DC microgrid is used for fast active power control and wider system frequency support. A virtual admittance method is also utilised to enhance the local DC microgrid voltages during the AC frequency events and DC fault test scenarios. The effectiveness of the control strategy is evaluated by simulation studies in MATLAB/Simulink.

d.c. distribution networks interfaced by two-level voltage source converters (VSCs) are characterised by rapid fault current development, which places severe time constraints on d.c. protection. A proposed solution to ease this is the implementation of advanced converters with current management capabilities such as modular multilevel converter (MMC). However, the limited fault current caused by MMC will make the widely used LV current-based protection less effective. A new method, targeted utility-scale LVDC distribution networks at conditions with limited fault current, combining dv/dt and di/dt has been proposed in literature with promising results for fast and selective protection. However, further investigation must be carried out to determine its applicability and limitations for protecting future compact d.c. distribution systems. This paper presents an investigation into the selective capabilities of the combined dv/dt and di/dt protection technique for a range of fault scenarios. The study considers the effects of sampling frequency, fault locations, and the network architecture with the aim of determining the limitations of the protection method. A simplified converter model with active fault current limiting and blocking capabilities is built in PSCAD/EMTDC and implemented in a radial and ring compact d.c. distribution network to facilitate the study.

This paper reviews the state of the art of DC fault discrimination and detection methods of HVDC grids, and summarises the underlying principles and the characteristics of each method. To minimize HVDC grid disturbance and power transfer interruption due to DC faults, it is critically important to have protection schemes that can detect, discriminate and isolate DC faults at high speeds with full selectivity. On this basis, this paper lists the advantages and disadvantages of the most promising fault detection methods, with the aim of articulating the future directions of HVDC protection systems. From the qualitative comparison of relative merits, the initial recommendations on HVDC grid protection are presented. Moreover, a comprehensive quantitative assessments of different fault detection methods discussed above are carried out on a generic 4-terminal meshed HVDC grid, which is modelled in PSCAD environment. The presented simulation results identify that the voltage derivative and wavelet transform are the most promising methods for DC fault detection and discrimination.

Low Voltage Direct Current (LVDC) distribution is one of the new promising technologies that has been introduced for the integration of renewables and powering certain applications. However, DC protection is still considered as one of the outstanding challenges that hold back the wide deployment of LVDC in the last mile utility applications. Most of existing DC solutions have been designed for specific application, however, their suitability for providing a good level of protection and safety for an LVDC last mile distribution network is still not clear. Therefore, this paper extensively evaluates the performances of different DC protection solutions on an active LVDC last mile distribution network with local generation sources (including PVs and battery storages). Based on the findings, recommendations of LVDC protection are presented in the paper for the resilient operation of future LVDC last mile distribution networks.

Low Voltage Direct Current (LVDC) distribution systems are one of the emerging technologies to recently attract attention for more efficient use of energy, and wider uptake of distributed renewables and energy storage. They do however present significant fault protection and safety challenges, which are not possible to address without using advanced protection techniques. Therefore, this paper considerably reviews these key challenges, and presents experimental results of prototyping an advanced protection scheme developed to help enable LVDC distribution networks for utility applications. The developed scheme is a DC current direction-based using multiple intelligent electronic devices (IEDs) relays in combination with controllable solid-state circuit breakers to detect and locate DC faults, and provide selective protection tripping within sub-millisecond timescales. A scaled laboratory demonstrator that emulates an LVDC distribution network is used as a test platform. It allows the characterisation of the transient behaviour for various fault conditions and locations. The developed protection algorithm is implemented in LabVIEW, and its performance against such fault conditions is tested within this environment.

Low voltage direct current (LVDC) distribution systems have the potential to support future realisation of smart grids and enabling of increased penetration of distributed renewables, electric vehicles, and heat pumps. They do however present significant protection challenges that existing schemes based on DC fuses and conventional electro-mechanical circuit breakers (EMCBs) cannot manage due to the nature of DC faults and slow device performance. Therefore, this paper presents an advanced protection scheme that addresses the outstanding challenges for protecting an LVDC last mile distribution network. The scheme takes advantage of advanced local measurements and communications that will be naturally integrated in smart grids, and the excellent level of controllability of solid state circuit breakers. It thus provides fast DC fault detection and interruption during DC transient periods in addition to achieving fault limitation and fast reliable restoration. The introductory part of the paper quantifies the potential benefits of LVDC last mile distribution networks, and discusses the potential LVDC architectures that best utilise the existing plant. Based on the new LVDC architectures, a typical UK LV network is energised using DC and modelled, and used as a case study for investigating the protection issues and evaluating the new protection scheme performance through simulation.

In power network analysis it is increasingly desirable to implement controller and power systems models within different software environments. This stems from, among other things, an increasing influence of new and distrib-uted control functions within smart grids and a growing influence of market operations. The computation time re-sulting from use of multiple simulation environments can cause significant delays and constrain the number of scenarios considered. This paper introduces and com-pares several techniques for integrating external control system models into power systems models for time do-main simulations. In particular, a new technique is reported in this paper for PowerFactory-MATLAB/Simulink co-simulation interfaces, which offers a significant advantage over alternative methods in terms of the reduction in simulation runtimes and flexi-bility for the end user.

High Voltage Direct Current (HVDC) grid concept has recently been introduced as the next step to the point-to-point HVDC links to maximise the benefits of more power flow share, and reduce the impact of renewables intermittency. However, the integration of DC grid within existing AC systems is complex and very challenging. The compatibility between the two systems under different operating conditions needs to be fully understood. This will require sophisticated models and analysis of their behaviour using powerful tools. This paper presents a representative dynamic model of a hybrid AC-DC gird, and investigates the transient and dynamic interaction between the AC and DC grids under different fault conditions. The model represents a reduced AC UK power system interfaced to a detailed four-terminal DC grid. The developed mode is built in Real Time Digital Simulation (RTDS) using dual time steps simulation techniques.

In the context of the energy trilemma (the provision of sustainable, affordable, reliable energy) the application of Low Voltage Direct Current (LVDC) distribution offers several advantages over the incumbent AC distribution system. LVDC distribution can increase the power transfer capability of existing cable assets while reducing the converter complexities required to integrate distributed generators and modern electrical loads to the network. This paper evaluates the technical potential for LVDC street lighting and integrated electric vehicle charging points by considering existing cable specifications, protection schemes and overall system efficiency. The first author was supported by EPSRC Centre for Doctoral Training in Future Power Networks and Smart Grids (EP/L015471/1) with industry support from Rolls-Royce plc. No new data was collected or generated during the course of the research.

Low Voltage DC (LVDC) distribution systems are new promising technologies which can potentially improve the efficiency and controllability of existing LV distribution networks. However, they do introduce new challenges under different fault conditions. Therefore, this paper investigates the performances of an active LVDC distribution network with local solar photovoltaics (PVs) and energy storages under different short-circuit faulted conditions. A typical UK LV distribution network energized by DC is used as a test network, and modeled using PSCAD/EMTDC. The LVDC is interfaced to the main AC grid using fully controlled two-level voltage source converter (VSC), and supplies DC and AC loads through DC/DC converter and DC/AC converter respectively. The response of an LVDC with such converters combination with different topologies and fault management capabilities are investigated through the simulation analysis.

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.

Low Voltage DC (LVDC) distribution systems have the potential to be considered as an efficient platform for facilitating the connection of more distributed energy resources. The applications of LVDC are still at an early stage due to the lack of mature experience and standards. Over and above, the protection challenges that are presented by integrating DC installations in existing AC systems are one of the key issues that are delaying the wide uptake of LVDC technologies. In response to these issues, this paper discusses the international installation progress of LVDC systems and their relevant standards in different sectors. This includes data centres, buildings, and utility last mile distribution systems. The paper also investigates the impact of using traditional LV protection methods on the performance of a faulted LVDC network, and on the associated post-fault power quality performance. A typical UK LV network is energised using DC and modelled in PSCAD, and used for the protection studies under different DC fault conditions.

The drive to reduce reliance on fossil fuel generation in meeting power system demand is encouraging network operators to develop novel methods of making greater use of available network capacity whilst maintaining stability and security. Challenges relating to network stability are particularly acute on islanded networks. The Northern Isles New Energy Solutions (NINES) project is implementing novel techniques for managing the power network on the Shetland Islands in the UK. Active Network Management is used to monitor and control the network and new wind generation in real time, and flexible demand is scheduled to minimise the use of conventional generation by reducing wind curtailment and minimising system losses. The flexible demand devices deployed also have the ability to respond to frequency therefore supporting system stability. This paper presents the development of two novel modelling techniques used in the design and deployment of NINES – an ‘envelope of stability wind generation’ and the use of Dynamic Optimal Power Flow to schedule flexible demand. A case study is presented which shows that an ANM scheme managing flexible demand has the potential to increase wind capacity connected on Shetland from the existing 4MW to 16.1MW. The management of domestic demand flexibility is shown to contribute up to 6.5GWh towards the reduction in conventional generation or up to 16.6GWh if domestic demand provides frequency response.

Low Voltage Direct Current (LVDC) systems have recently been recognised as one of the key enabling technologies that can facilitate the connection of more distributed renewables with improved efficiency and enhanced controllability. This is in addition to the potential provision of increased power flow capacity which is required to meet the anticipated growth in electric transport and heat demand. However, there is still a shortage of mature experience and practical technical solutions that can support the uptake of such systems and increase commercial interest. One of the barriers is the lack of standards necessary to increase industry confidence and for the development of cost effective technical solutions that will accelerate the commercialization of LVDC technologies. Most of the existing international standards focus on alternating current (ac) systems with limited areas covering direct current (dc). Recently, new standard activities at national and international levels have begun to cover specific LVDC applications. However, it is still not clear whether these activities, in addition to existing standards, are sufficient and comprehensive to provide the necessary tools for best practice system design. This paper therefore reviews and evaluates the available LVDC standards within the context of the establish ac system to determine the state of the art of dc standardization and the areas where future work is required.

In addition to other measures such as energy saving, the adoption of a large amount of microgeneration driven by renewable and low carbon energy resources is expected to have the potential to reduce losses associated with producing and delivering electricity, combat climate change and fuel poverty, and improve the overall system performance. However, incorporating a substantial volume of microgeneration within a system that is not designed for such a paradigm could lead to conflicts in the operating strategies of the new and existing centralized generation technologies. This paper investigates the impact of tripping substantial volumes of LV connected microgeneration on the dynamic performance of a large system during significant low frequency events. An initial dynamic model of the UK system based on a number of coherent areas as identified in the UK Transmission Seven Year Statement (SYS) has been developed within a real time digital simulator (RTDS) and this paper presents the early study results.

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.

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.

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.

In the future millions of homes in the UK may have the appropriate characteristics to facilitate the deployment of existing micro CHP technologies, and establish "personal power stations", using different types of distributed energy resources (DERs). The micro CHP technologies to be accommodated at houses are typically driven by single-phase generators at 230 V. However, the integration of a large number of such single-phase generators may lead to changes in the behaviour of the system in both normal and abnormal operation. This paper focuses on investigating the performance of an LV distribution network with high penetration of DERs under abnormal conditions. For this investigation the DERs are based on directly- connected single-phase generators and converter-connected generation. The contribution of these sources to network fault levels and their impact on overcurrent protection schemes are assessed in order to outline the protection requirements in future LV distribution networks with active power sources located at each home.

DC microgrids are capable of integrating and coordinating distributed energy resources into power systems, along with providing services to the wider system e.g. balancing, frequency support, demand response, etc. This paper investigates the capability of DC microgrids providing grid frequency support, for the GB Enhanced Frequency Response service. In this study, photovoltaic generation, energy storage, and load, form the DC microgrids. The control strategy is a decentralised scheme, based on conventional droop control for active power sharing and grid frequency support. Droop control is also used within the DC microgrid for power sharing amongst generation and load. Scenarios are conducted to evaluate the effectiveness of the control strategy and verified by MATLAB/Simulink simulations.

Low voltage direct current (LVDC) distribution systems have recently been considered as an alternative approach to provide flexible infrastructure with enhanced controllability to facilitate the integration of low-carbon technologies (LCTs). To date, there is no business-as-usual example of LVDC for utility applications and only few trials have been developed so far. The deployment of LVDC in general will present revolutionary changes in LV distribution networks. This will require are thinking of network design principles and the enablement of integrated solutions. This discussion paper reviews the current practice in utility-scale LVDC distribution networks worldwide. The paper also presents a new multi-zone architecture approach which can be used to better understand future of LVDC systems, and exploit their inherent flexibility to allow synergistic integration of multiple energy technologies.

The gradual deployment of intelligent and coordinated devices in the electrical power system needs careful investigation of the interactions between the various domains involved. Especially due to the coupling between ICT and power systems a holistic approach for testing and validating is required. Taking existing (quasi-) standardised smart grid system and test specification methods as a starting point, we are developing a holistic testing and validation approach that allows a very flexible way of assessing the system level aspects by various types of experiments (including virtual, real, and mixed lab settings). This paper describes the formal holistic test case specification method and applies it to a particular co-simulation experimental setup. The various building blocks of such a simulation (i.e., FMI, mosaik, domain-specific simulation federates) are covered in more detail. The presented method addresses most modeling and specification challenges in cyber-physical energy systems and is extensible for future additions such as uncertainty quantification., Comment: 2017 Workshop on Modeling and Simulation of Cyber-Physical Energy Systems (MSCPES)

LVDC distribution systems have the potential to support future realisation of smart grids functionality. They do however present significant protection challenges that existing schemes based on DC fuses and conventional circuit breakers cannot manage due to slow device performance. Therefore, this research introduces an advanced protection scheme that addresses the outstanding challenges facing realisation of last mile DC distribution. The developed scheme has been validated using experimental testing.

LV direct current (LVDC) distribution systems have recently been considered as an alternative approach to electrical distribution system infrastructure as they possess the flexibility and controllability that is required to facilitate the integration of low carbon technologies (LCT). For example, energising existing LV AC cables by DC with higher voltages (>0.4kV) can potentially release additional power capacity on LV cables and reduce the associated thermal losses. However, converting existing AC cables for DC operation may change the cable performance under faulted conditions, resulting in a change to its lifetime. The nature of future LVDC systems can be capacitive due to the characteristic of particular customers such as battery energy storage systems (BESS) and electric vehicles (EVs). A short-circuit fault on the DC side may lead to a discharge/release of significant transient energy in LV cables which was never anticipated under traditional LVAC networks. This paper quantifies the transient DC fault let-through energy which can be imposed on existing AC cables used for DC operation, and draws conclusions on the potential impact of such phenomena on the cable performance. A detailed model of an LVDC test network with three-core LV cables is developed using PSCAD/EMTDC for simulation studies.

Low voltage direct current (LVDC) distribution systems have the potential to be considered as an enabler of increased penetration of distributed renewables, electric vehicles, and heat pump systems. They do however present significant challenges for understanding fault behaviour and effective protection systems. This paper presents these challenges, and investigates the effectiveness of using IEC61660 for the short-circuit characterisation of LVDC networks.

In addition to the anticipated gradual reduction of system inertia in the future, its variability due to more flexible system control and management over time will also be an issue in future power system operation. This paper focuses on the impact of inertia reduction and variation on existing frequency-based protection during loss of large infeed contingency, with the UK power system used as a basis for the studies conducted. Two protection issues are identified by evaluating the impact of variable system inertia under different system conditions: the 1Hz/s RoCoF setting proposed by the UK distribution code review panel cannot effectively stabilise anti-islanding protection in locations relatively closer to the disturbance in future networks with the planned increase of infrequent infeed loss; underfrequency load shedding (UFLS) (based on existing settings) in a relatively weak system where load is mainly supported by naturally low inertia renewables may mal-operate more often which results in more interruptions to customers. In order to maintain system stability and integrity against aforementioned protection issues, three alternative methods are discussed with a focus on regional based adaptive protection.

Future HVDC grids are expected to incorporate different power converters from multiple vendors in the same system. Even if a complete converter station is developed by a single manufacturer, it might be challenging to integrate this terminal into a DC grid that comprises of several converter stations built by other vendors. Moreover, the different fault response exhibited by each converter technology complicates the design of HVDC protection systems. Therefore, this study investigates the fault response of a multivendor HVDC grid. An illustrative 4-terminal meshed HVDC grid, which is modelled in PSCAD environment, is used to perform studies of interoperability of different converter topologies on a common HVDC network. The investigation of the fault behaviour of such a multivendor HVDC network highlights the main impediments that need to be tackled and a set of actions that needs to be done at a converter level in order to mitigate the impact of DC faults on the HVDC system. Moreover, the key parameters that need to be taken into account when designing a protection scheme for a multivendor HVDC grid are identified.

Low Voltage Direct Current (LVDC) distribution is one of the new promising technologies that have the potential to accelerate the wider integration of distributed renewables. However, adding new power electronics to convert AC to DC will introduce new forms of faults with different characteristics. Converters with inherent fault current limiting and blocking capabilities will significantly limit the fault currents, resulting in significant impacts on the performance of existing LV overcurrent protection schemes. New protection methods based on the change in the DC voltages have been proposed recently by different researches. The issue with these methods is that the protection relays of the un-faulted feeders will also see the same change in the voltage for certain faults, leading to substandard selectivity and unnecessary tripping. This paper investigates these challenges, and presents a novel DC protection method which is based on the use of the combination of two components: the voltage change (dv/dt) and the change of current (di/dt). The new method is mainly developed to detect and locate DC faults with reduced fault current levels within DC distribution networks. The introduced protection concept is tested on an LVDC distribution network example using PSCAD/EMTDC simulation tool.

Rising fault levels are becoming increasingly problematic in the UK distribution network, with large sections of the network operating near to its designed fault level capability. With the increase in penetration of distributed generation that is expected in the coming years, this situation is becoming more pressing. Traditional methods of dealing with the issue may not be appropriate - upgrading plant is expensive and disruptive, while network reconfiguration can compromise security of supply. Superconducting Fault Current Limiters (SFCLs) are emerging as a potential solution, with installations now taking place in several locations worldwide. The integration of an SFCL into a network involves a number of challenges, particularly concerning the coordination of protection systems. The operation of existing protection schemes may be compromised due to the increased resistance in the network during a fault (in the case of a resistive SFCL). Furthermore, the reduction in fault levels, although desirable, can have a detrimental impact on protection operating times. This paper will consider an existing medium voltage network in the UK, which incorporates distributed generation capacity. The performance of IDMT overcurrent and distance protection schemes will be examined when an SFCL is installed in this network. In particular, the increased operating time of overcurrent relays will be discussed along with grading implications. The impact on distance protection reach will also be examined. A variety of network operational scenarios including SFCL placement and fault conditions will be considered and compared. Recommendations will be made in terms of protection settings and SFCL placement in order to mitigate the aforementioned issues.

Smart grid systems are characterized by high complexity due to interactions between a traditional passive network and active power electronic components, coupled using communication links. Additionally, automation and information technology plays an important role in order to operate and optimize such cyber-physical energy systems with a high(er) penetration of fluctuating renewable generation and controllable loads. As a result of these developments the validation on the system level becomes much more important during the whole engineering and deployment process, today. In earlier development stages and for larger system configurations laboratory-based testing is not always an option. Due to recent developments, simulation-based approaches are now an appropriate tool to support the development, implementation, and roll-out of smart grid solutions. This paper discusses the current state of simulation-based approaches and outlines the necessary future research and development directions in the domain of power and energy systems.