Analysis of protection issues in autonomous mv micro-grids

Due to the increased complexity of distribution networks and the commitment to offer high quality electricity from distributed generation, in terms of reliability and security, conventional strategies in the design of protection schemes are overcome by the great challenges in maintaining the stability and safety of the microgrid. This document evaluates the impact that penetration of distributed generation has on protection schemes designed for conventional distribution networks. It also presents guidelines for actions that may be taken in order to mitigate the impact of distributed generation in coordination protection schemes.

Implementation of micro grid concept creates several issues to the existing protection scheme in the radial distribution network. Depending on the location and capacity of the distributed generators, the short-circuit current from the main grid and distributed generations causes variations in the fault current levels inside the micro grid. The changes cause effect of sympathetic tripping, blinding of protection, relay over-reaching, relay under-reaching and loss of selectivity of the overcurrent protection scheme. Such issues must be managed carefully to ensure full benefit from micro grid adaptation. Conventional protection schemes are unable to detect fault current levels common in micro grid. Several methods have been proposed in various research paper. Micro grid protection is substantial to provide reliable and continuous power supply to the customers. The main aim of proposed work is to detect the fault for fast restoration of the system back to the normal operation. The proposed protection scheme for micro grid uses intelligent electronics device for detecting the fault

The high-level proliferation of inverter-interfaced distributed generators (IIDGs) in modern distribution networks (DNs) has changed system topologies and fault current signatures, which compromises the protective relays in DNs. Investigating IIDG fault behaviors-based protection scheme will benefit the grid’s safety and stability. This paper proposes a novel current differential protection (CDP) scheme that considers the delay behaviors of positive- and negative-sequence component extractors for IIDGs in DNs. A frequency-domain analytical model of the fault current for a grid-connected IIDG with the PQ control strategy and a low-voltage ride-through (LVRT) capability is investigated. The dynamic behavior of the IIDGs considering the sequence-component extractor based on the Pade approximation is presented, where the T/4 delay extractor of the IIDGs causes a two-stage behavior in the fault transient process. It is found that a 5 ms error between the measured and actual values after the fault will affect the transient characteristics of the IIDGs. The transient current generated by the IIDGs during grid faults contains a large number of low-order harmonic components within the range of 0–200 Hz, which is significantly different to the current provided by the power grid. Therefore, the proposed CDP scheme uses protective relays at both terminals to obtain the required transient electric quantity using the Prony method. By constructing the frequency-characteristics ratio (FCR) and the exchanging FCR between two terminal relays, the developed protection criteria are implemented. The accuracy of the fault analysis method, whose maximum computational error is below 0.1%, and the feasibility of the proposed protection scheme are demonstrated by using a 10 kV DN in a PSCAD/EMTDC simulation, which can be applied to various fault conditions and traditional DNs without IIDGs.

Protection of microgrid has become challenging due to the hosting of various actors such as distributed generation, energy storage systems, information and communication technologies, etc. The main protection challenges in the microgrid are the bi-directional power flow, protection blinding, sympathetic tripping, change in short-circuit level due to different modes of operation, and limited fault current contribution by converter-interfaced sources. This paper presents a comprehensive review of the available microgrid protection schemes which are based on traditional protection principles and emerging techniques such as machine learning, data-mining, wavelet transform, etc. A categorical assessment of the reviewed protection schemes is also presented. The key findings of the paper suggest that the time-domain and communication-assisted protection schemes could be suitable solutions to address the identified protection challenges in the microgrid.

Microgrid protection schemes play a vital role in ensuring the reliability and efficiency of power distribution in urban and rural areas, especially as renewable distributed energy resources are increasingly integrated. This paper aims to provide a comprehensive analysis of existing microgrid protection schemes, discussing their advantages and limitations and highlighting key challenges and opportunities for future research. As microgrid systems become increasingly common, the management of power flow in small-community networks equipped with intelligent electronic devices, non-linear loads, and multiple distributed generation sources becomes more complicated. In order to address these challenges, coordination of protective schemes is required to prevent overload and damage to equipment. Firstly, the study discusses microgrid definitions and functional categories, highlighting their benefits and drawbacks. An analysis of microgrid protection literature includes adaptive protection systems as intelligent methods to address coordination challenges. Secondly, this review classifies microgrid protection techniques as modified, new knowledge-based and conventional schemes and provides a systematic analysis of optimization approaches. The study also examines the essential problems associated with the coordination of protective relays within microgrids. Finally, examining the current state of microgrid protection to identify the key research directions and opportunities for future development in this rapidly advancing field. The findings of this comprehensive analysis highlight the importance of effective microgrid protection in ensuring a stable and sustainable energy future.

A differential protection scheme for the ring microgrids based on the power change rate of the bus is proposed. By setting the power change rate on both sides of the bus as the differential amount, the power change rate is maximized at the moment of short-circuit, which can immediately indicate whether a fault has occurred. Compared to the protection scheme that uses the current for fault identification, the proposed scheme reduces the time for the fault current to increase to the action threshold, saves the time required for fault detection. Moreover, it is proportional to the square of the current, and the higher orders increase the speed of the change rate, meanwhile, it is proportional to the short-circuit impedance which broadens the fault identification range and improves the protection sensitivity. Finally, the results of simulations prove that the proposed protection scheme has improved speed, sensitivity, and interference resistance while maintaining good selectivity for differential protection.

The low-voltage dc (LVDC) microgrid possesses numerous benefits and their penetration in the power system has increased rapidly in recent years. However, the detection of faults in the LVDC microgrid is a challenging issue due to the large magnitude of fault currents and fault-level variation in the microgrid. The performance of the recent current and its derivative-based protection scheme is limited in case of faults in the islanding mode of operation, different microgrid topologies, varying distributed generations (DGs) penetration, and against the measurement noise. This article presents an enhanced differential protection scheme for LVDC microgrid integrated with multiple DGs and storage. The differential current and its first derivative are processed through the decision tree (DT) algorithm for fault detection and the K-nearest neighbor (KNN) technique is utilized for fault classification. The robustness of the proposed protection scheme is tested for different fault types and fault conditions with variation in microgrid topology and operating conditions. The impact of the intermittent and volatile nature of the DGs, the presence of measurement noise, and assessment during external faults and critical no-fault cases have been investigated. The proposed scheme is tested on the MATLAB/ SIMULINK and validated on the Typhoon HIL platform for the assessment of real-time performance. The test results show that the proposed scheme can detect and classify faults with high accuracy and faster response time and, thus, can be a potential candidate for providing dependable protection measures for LVDC microgrids.

The telecommunication, broadcasting and other instrumented towers carry power and/or signal cables from their ground end to their upper regions. During a direct hit to the tower, significant induction can occur to these mounted cables. In order to provide adequate protection to the equipments connected to them, protection schemes have been evolved in the literature. Development of more effective protection schemes requires a quantitative knowledge on various parameters. However, such quantitative knowledge is difficult to find at present. Amongst several of these aspects, the present work aims to investigate on the two important aspects: (i) what would be the nature of the induced currents and (ii) what will be the current sharing if as per the practice, the sheath of the cable is connected to the down conductor/tower. These aspects will be useful in design of protection schemes and also in analyzing the field structure around instrumented towers.

Microgrid protection schemes are different from those used in conventional distribution networks. With the incorporation of distributed generation (DG), and the ability for bi-directional power flow and island operation; the fault current and delay parameters of protective relays need to be recalculated and updated in response to the dynamic operation of microgrid. Performance evaluation (e.g. fault clearance time and recovery time) and parameter estimation (fault current and trip delay) for such a protection scheme have been difficult because they require comprehensive modeling of electrical network, IED behaviors, and IEC61850-based communication. In this paper, we present a centralized scheme with detailed modeling and co-simulation of all these aspects. We also demonstrate how the analysis of the simulation results helps overcoming the forth-mentioned difficulties.

Recent times have witnessed increasing utilization of wide area measurements to design the transmission line protection schemes as wide area measurements improve the reliability of protection methods. Usage of ICT tools for communicating sensor measurement in power networks demands immunity and resiliency of the associated protection scheme against false data injection attack (FDIA). Immunity against malicious manipulation of sensor information is attainable by securing the communication channels connecting the sensors through cryptographic protocols, and encryption. However, securing all the sensors and communication channels is economically unviable. A practical solution involves securing a reduced set of sensors without compromising fault detection accuracy. With the aim of developing a simple, economically viable and FDIA resilient scheme under the assumption that the adversary has complete knowledge of the system dynamics, the present work proposes a logical analysis of data (LAD) based fault detection scheme. The proposed scheme identifies the minimal set of sensors for FDIA resiliency and detects the state (faulty or healthy) of the power network relying on the measurements received from the ‘minimal sensor set’ only. Validation of the proposed protection scheme on IEEE 9-bus system reveals that in addition to being FDIA resilient, it is reliable and computationally efficient.

A novel protection scheme for low voltage DC microgrid using inductance estimation

MODWT-XGBoost based smart energy solution for fault detection and classification in a smart microgrid

One major concern of the industry park (IP) with independent power producers (IPPs) is the protection scheme design, especially when the tie-line with the main grid is suddenly tripped due to some external faults. Under the worst scenarios, the IP may be completely shut down if no proper protection scheme is considered. In order to avoid such possible blackouts, it is necessary to design the relay setting along with appropriate load shedding (LS) schemes and generators’ dynamic braking (DB) to maintain the balance between available generation and load, as well as to restore the system frequency and the voltage magnitude. In this paper, the expansion of production in one IP will be considered with deploying additional generators. Extensive numerical simulations under various contingencies are conducted to study dynamical interactions between relay settings and LS/DB mechanisms of this IP. possible Recommendations of revising current protective relay settings and appending an under-frequency relay at the point of common connections (PCC) are comprehensively investigated such that all loads and generation units in this IP still can sustain the unexpected power system disturbances caused by fault contingencies in the main utility system.

The DC microgrid has become a typical distribution network due to its excellent performances. However, a well‐designed protection scheme still remains to be a challenge for DC microgrids. This paper proposes a fault distance estimation‐based protection scheme for DC loop‐type microgrids relying on two‐terminal electrical quantities. Different from the traditional methods, a small inductor is implemented at each head of the line instead of obtaining the derivative of fault current using current difference value. Thus, the derivative of currents can be calculated accurately with the measured voltages on the small inductors during faults. The presented protection method is able to realise fault location and fault isolation quickly and accurately. Furthermore, it is immune to fault resistances. The presented protection scheme has been tested and verified through PSCAD/EMTDC simulations. The results prove that the new protection scheme possesses the excellent performance.

Recently, researchers have started exploring the design of route protection schemes that ensure networks can sustain traffic demand without congestion under failures. Existing approaches focus on ensuring worst-case performance over simultaneous f -failure scenarios is acceptable. Unfortunately, even a single bad scenario may render the schemes unable to protect against any f -failure scenario. In this paper, we present Lancet, a system designed to handle most failures when not all can be tackled. Lancet comprises three components: (i) an algorithm to analyze which failure scenarios the network can intrinsically handle which provides a benchmark for any protection routing scheme, and guides the design of new schemes; (ii) an approach to efficiently design a protection schemes for more general failure sets than all f -failure scenarios; and (iii) techniques to determine which of combinatorially many scenarios to design for. Our evaluations with real topologies and validations on an emulation testbed show that Lancet outperforms a worst-case approach by protecting against many more scenarios, and can even match the scenarios handled by optimal network response.