Performance analysis of the overcurrent protection for the renewable distributed generation dominated microgrids

This paper aims to present a study of the conventional protection scheme i.e. overcurrent (OC) protection’s malfunctioning in the microgrids dominated by inverter interfaced distributed generator (IIDG) under a range of scenarios by injecting faults at different locations of the network. Due to low cost and inherent back-up protection, overcurrent scheme is considered to be the main protection for the distribution networks and microgrids. However, the integration of IIDG in large number might introduce several protection challenges for microgrids. Existing literature discusses the protection issues that might arise in microgrids due to addition of distributed generation, but those challenges are not practically studied. Hence, in this paper, several fault cases are simulated by changing fault positions and using different combinations of IIDGs in the network so that protection challenges can be fully explored and performance of the overcurrent relays in the IIDG dominated microgrids can be analysed under those simulated cases

Detailed analysis of the future distribution network protection issues

This study will present the results of several simulation-based analyses investigating the performance of distribution network protection under a range of future scenarios. It is widely accepted that the integration of a significant amount of distributed generation, often from renewable energy sources and interfaced to the main network via power electronics converters, will be commonplace in the future. Furthermore, at the transmission level, the interconnection of different countries through HVDC links and the decommissioning of many large-scale conventional synchronous generators will result in the power systems becoming progressively weaker in terms of reduced faults level and lower system inertia. This study will, therefore, illustrate and emphasise the challenges and issues that arise in future distribution networks protection due to reduced system strength, fault level and the changing nature of the contribution (both in terms of magnitude and possibly delay in provision) to fault levels and the possible impact this may have on traditional overcurrent based protection schemes by building a simple model of distribution network in Simulink, MATLAB. In addition to that, the paper will also discuss some potential solutions as novel schemes to tackle the arising protection related problems

Review and evaluation of protection issues and solutions for future distribution networks

This paper presents a comprehensive review and detailed investigation of the protection issues that may potentially arise due to the proliferation of technologies such as distributed generator (DG) and energy storage in future power distribution networks. A summary and critical evaluation of several potential protection and control solutions (applicable to the generators or the network), which are proposed as addressing one or more of the identified issues, are also presented. The analysis covers both economic and technological viability and feasibility. Finally, a mapping of the identified issues to the most appropriate proposed solutions is presented, along with discussion, analysis and conclusions

A communication-free active unit protection scheme for inverter dominated islanded microgrids

Large-scale integration of different renewable energy resources introduces significant challenges to the protection of microgrids (particularly those that may operate in islanded mode), including variable and low fault levels, difficulty in operation of main and backup protection with their coordination, and bidirectional power flow during faults. As a solution to such challenges, this paper presents a novel active protection strategy for the inverter dominated islanded microgrids that coordinates protection actions with the inverter control strategy. The proposed scheme dictates specific actions from the inverter interfaced distributed generator (IIDG) controller to inject specific harmonic components into the microgrid during the fault. Relays throughout the network detect and analyse the injected harmonic components to identify the faulted section, and take appropriate isolating actions, without any requirement for relay-to-relay communication. The scheme achieves selectivity and coordination using definite time delay settings. To verify the performance of the scheme, a realistic microgrid model incorporating the proposed protection strategy has been developed in MATLAB Simulink, where a wide range of fault scenarios have been simulated with variations in fault location, type, fault resistance, line impedance, and different combinations of IIDGs (including with and without connection of a synchronous generator). Additionally, case studies using a real-time digital simulator (RTDS) platform have also been conducted to validate the performance of the proposed solution in real-time, with multiple relays implemented as hardware prototypes running on the OPAL-RT platform – thereby demonstrating the system operation in a hardware-in-the-loop (HiL) configuration. It is shown that the scheme is highly effective in detecting and isolating faults, with proper discrimination, stability and provision of backup, under all investigated scenarios

Evaluation of fault characteristics in microgrids dominated by inverter-based distributed generators with different control strategies

This paper presents a comprehensive study of the fault current characteristics of microgrids dominated by Inverter-Based Distributed Generators (IBDGs) with different control strategies, with a view to identifying protection challenges and potential future solutions. Different combinations of control strategies, (i.e. PQ, V/F and droop control strategies) are deployed within different IBDGs, to represent typical microgrid operating scenarios and to investigate the impact of these strategies and types of IBDGs on the fault behavior of microgrids under islanded mode of operation. Various controllers are also deployed on the IBDGs at different physical locations in the system to investigate locational impact on microgrids fault behavior. Extensive simulation results will be presented and the impact of different control strategies and IBDG locations on the protection systems performance will be evaluated based on the results. Recommendations of how protection systems should take the various control strategies and locational impact into account to ensure reliable operation will also be discussed and future work will be outlined

Evaluation of Grid-Forming Converter's impact on distance protection performance

Motivated by the net-zero carbon emission target, the GB transmission system has seen a massive increase in the amount of Converter Based Resources (CBRs). Grid-Forming Converters (GFMs) have attracted significant interests for supporting the future system operability with high penetration of renewables due to their various more desirable properties compared with Grid-Following Converters (GFLs), e.g., stronger capability to operate in weak grids. Recent research work has found that Fault-Ride Through (FRT) strategies of CBRs have significant impact on the distance protection performance, and comprised protection operation was observed when synchronous generation sources were replaced with CBRs. However, existing research work has mainly focused on the impact of the GFLs’ FRT on distance protection, while the impact of GFMs, which could have very different FRT strategies, has not been comprehensively investigated. In this paper, a GFM with two typically used FRT implementations, i.e., the current control based FRT and the virtual impedance based FRT, is developed in the Real-Time Digital Simulator (RTDS) and the impact of the two FRT methods on distance protection is investigated for both balanced and unbalanced fault conditions. By comparing the relay performance with two FRT strategies, it is found that the distance protection appears to have better performance in terms of faulty phase selection, accurate impedance measurement and impedance measurement stability when the virtual impedance-based FRT is adopted by the GFM

Comparative evaluation of dynamic performance of virtual synchronous machine and synchronous machines

Increasing penetration of converter-interfaced renewable generation has led to significant operational challenges for power systems. Such challenges are mainly caused by the different capabilities and dynamic responses of the converters compared with synchronous machines, e.g. converters do not naturally provide inertia to the system and contribute limited fault level with very different fault characteristics. Virtual Synchronous Machines (VSM) and Synchronous Condensers (SCs) are both considered as promising solutions to address the challenges in operating converter-dominated power systems. This paper presents comprehensive studies for evaluating and comparing the dynamic performance of VSM, SC and Synchronous Generators (SGs), under a range of grid contingency events, which include short circuit faults, frequency disturbances, voltage depression, etc. The studies aim to offer insights on the level of support VSMs can offer to the system as compared with SCs and SGs, and their advantages, potential issues and limitations that need to be considered for a wider application in the system. From the studies, it is found that the VSM system appears to have comparable performance and support to the system from the perspective of fault ride-through (FRT), provision of inertial response and reaction to voltage steps. However, while VSM can potentially provide a fast fault current injection through the implementation of appropriate control, a key limitation is on the magnitude of fault currents, so it is unlikely to be capable of offering the same level of support compared with SCs and SGs

Experimental assessment and validation of inertial behaviour of virtual synchronous machines

Increasing integration of converter-interfaced renewable generation has led to significant operational challenges for power systems. Such challenges are mainly caused by the different capabilities and dynamic responses of the converters compared with synchronous machines, for example, converters do not naturally provide inertia to the system. Virtual Synchronous Machine (VSM) is considered as a promising solution to address the challenges associated with reduced system inertia via the provision of emulated inertial response to support the operation of converter-dominated power systems. However, it has been observed that the dynamic behaviour of the VSM could differ significantly from that of a Synchronous Condenser (SC) and a Synchronous Generator (SG) in terms of inertial response provision, even when the VSM is configured with the same inertia constant. Furthermore, effective practical methods for evaluating the damping performance of VSMs are not presently available. To gain a better understanding and achieve a more accurate assessment of the dynamic inertial and damping performance of VSMs, this paper presents an experimental methodology for systematic evaluation of the dynamic response of the VSM in the frequency domain using the Network Frequency Perturbation (NFP) method. Experimental design and implementation of the NFP method are presented to assess VSM system's equivalent inertia and damping constants, where the VSM system under test can be treated as a black box without any knowledge of internal settings and control design. Case studies are conducted, where the proposed experimental design has been applied for testing and assessing the inertial and damping constants of a physical 246 kVA VSM prototype driven by a Battery Energy Storage System with comparison of the SC and SG with equivalent inertia constant. Power-Hardware-in-the-Loop (PHiL) testing is also conducted to demonstrate the VSM's inertia performance. The studies demonstrate that the developed experimental approach based on NFP method provides a valuable tool for network operators and manufacturers for evaluating the inertial and damping performance

A clinical study of arrhythmias associated with acute coronary syndrome: a hospital based study of a high risk and previously undocumented population

Background: ACS represents a global epidemic. Arrhythmia in ACS is common. Careful investigation may lead to further improvement of prognosis. Retrospectively analyzed the year- round data of our center. Study was undertaken to analyze the incidence, frequency and type of arrhythmias in ACS. This is to aid timely intervention and to modify the outcome. Identification of the type of arrhythmia is of therapeutic and prognostic importance.Methods: This cross sectional analytical study was conducted in the Department of Cardiology, Apollo Hospitals Dhaka, from January 2019 to January 2020 with ACS patients. Enrolled consecutively and data analyzed.Results: There were 500 patients enrolled considering inclusion and exclusion criteria. Sample was subdivided into 3 groups on the type of ACS. Group-I with UA, Group-II with NSTE - ACS and Group-III with STE - ACS. Different types of arrhythmia noted. Types of arrhythmia were correlated with type of ACS. 500 patients included. Mean age 55.53±12.70, 71.6% male and 28.4% female. 60.4% hypertensive, 46.2% diabetic, 20.2% positive family history of CAD, 32.2% current smoker, 56.4% dyslipidaemic and 9.6% asthmatic. 31.2% UA, 39.2% NSTE-ACS and 29.6% STE-ACS. Type of arrhythmias noted. 22% sinus tachycardia, 20.2% sinus bradycardia, 9% atrial fibrillation, 5.2% ventricular ectopic, 4.8% supra ventricular ectopic, 2.8% bundle branch block, 2.2% atrio-ventricular block, 1% broad complex tachycardia, 0.4% narrow complex tachycardia, 0.2% sinus node dysfunction and 32.2% without any arrhythmia. Significant incidences of arrhythmia detected - respectively 29.8%, 39.2% and 31%, p<0.001.Conclusions: In conclusion, arrhythmias in ACS are common. More attention should be paid to improve their treatment and prognosis

Pulmonary Tuberculosis and Drug Resistance in Dhaka Central Jail, the Largest Prison in Bangladesh

There are limited data on TB among prison inmates in Bangladesh. The aim of the study was to determine the prevalence of pulmonary tuberculosis (TB), its drug resistance and risk factors in Dhaka Central Jail, the largest prison in Bangladesh.Cross sectional survey with, active screening of a total number of 11,001 inmates over a period of 2 years. Sputum samples from TB suspects were taken for acid- fast bacilli (AFB) microscopy, culture and drug susceptibility testing. (5.37, 4.02–7.16).The study results revealed a very high prevalence of TB in the prison population in Dhaka Central Jail. Entry examinations and active symptom screening among inmates are important to control TB transmission inside the prison. Identifying undiagnosed smear-negative TB cases remains a challenge to combat this deadly disease in this difficult setting