Protection Scheme For Distribution Networks Research Articles

Differential protection scheme for distribution network with distributed generation based on improved feature mode decomposition and derivative dynamic time warping

With the progress of communication technology, the cost of optical fiber and 5G continues to decrease, and data transmission becomes more convenient and fast, making it possible to realize differential protection of distribution network by various intelligent algorithms using signal waveforms. Aiming at the problem that the traditional relay protection device can not meet the actual demand when the single-phase ground fault occurs in the distribution network with distributed generation, this paper proposes a new differential protection scheme. The characteristic mode decomposition improved by the whale optimization algorithm is used to decompose the zero-sequence current waveform collected at both ends of the line. Based on the basic principle of current differential protection, the derivative dynamic time warping of the component with the largest fault feature can effectively solve the problem that the grounding current of the distribution network cannot meet the working requirements of the differential protection device, and ensure the safe and stable operation of the system. Finally, based on MATLAB software, the performance of this method is comprehensively evaluated by simulating different fault conditions, so as to ensure the feasibility and accuracy of this method in the case of diversified faults when the distributed generation is used as part of the power supply.

A Current Differential Protection Scheme for Distribution Networks with Inverter-Interfaced Distributed Generators Considering Delay Behaviors of Sequence Component Extractors

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.

Adaptive real-time protection scheme for distribution networks with high penetration levels of renewable energy resources

The increasing demands of electrical power have imposed a necessity to integrate renewable energy power sources (REPS) into electrical power networks. The presence of REPS within electrical distribution networks mandated an update in the settings of the overcurrent protection relays. In this paper, a real-time adaptive protection scheme is proposed to redefine the settings of the overcurrent protection relays by replacing the traditional time multiplier setting (TMS) with a newly proposed real-time adaptive time multiplier setting (ATMS). The proposed ATMS is formulated as the product of two factors namely; the acceleration factor (AF) and the tuning factor (TF). The AF is set as the ratio of the impedance seen by the relay during a fault to the pre-fault impedance. The TF is a multiplication constant that is determined offline prior to operation in order to optimize ATMS. The scheme was tested upon different radial and meshed bench-mark testing systems; the IEEE 34 system and the IEEE 30 bus system employing MATLAB software package. The proposed scheme proved its capability of optimizing the response of overcurrent relays and minimizing total operating time. In addition to its adaptability to different operational and loading conditions during the day.

Analysis of distribution network planning with distributed power supply based on ELM algorithm

Abstract With the development of the social economy, the importance of energy and environmental issues is becoming more and more prominent. Distributed power sources (DG) have the advantages of low carbon and environmental protection, flexible control, and low investment cost, but their nodes in the grid are random, which will increase the complexity and uncertainty of grid operation after grid connection. In this paper, we study the planning path of DGs in distribution networks and the protection technologies involved. Firstly, we focus on the impact of DG access on the protection of distribution networks and the impact of different access capacities and access locations of DG on the protection of distribution networks. Second, after studying the current status of the application of traditional genetic algorithms in distribution network fault location, a two-layer planning model based on the modified extreme learning machine algorithm (MPSO-ELM) is proposed, with the load demand guaranteed by the first layer of power allocation and the fault location incorporated into the distribution network protection scheme in the second layer. Finally, simulations are performed to compare and demonstrate the advantages of this MPSO-ELM algorithm. The simulation results show that the MPSOELM algorithm converges faster than the traditional genetic algorithm by 7s, the average operating speed of power nodes is 3.61ms faster than the traditional genetic algorithm by 5.59ms, and the accuracy in fault location is improved by 23.14%. The simulation results verify the comprehensiveness, accuracy, and high efficiency of the ELM algorithm for double-layer planning of distribution networks containing distributed power supplies, which is important for improving the level of power grid construction and avoiding the risk of power grid construction.

Adaptive overcurrent protection scheme for distribution networks with connection of mobile energy storage devices

The increasing penetration of renewable energy sources in distribution networks has caused great challenges to the reliable operation of the conventional overcurrent protection schemes. In particularly, serious underreach and overreach problems of protection scope may occur under the ever growing application of mobile energy storage (MES) devices. To improve the adaptability to the connection of MES devices under distribution networks, this paper proposes an adaptive overcurrent protection scheme, which can avoid the unfavorable effects caused by infeed currents and out flowing currents. Firstly, the effects of MES device on the protection scope of the overcurrent protection strategy are investigated, considering the charging, discharging, and backup operation modes of MES device. Secondly, to adapt to the different operation modes, the equivalent impedance of MES device is calculated, and then it is introduced to determine the adaptive settings of fast current protection and time-critical fast current protection. Finally, the constructed adaptive overcurrent protection scheme can adapt to varied fault conditions, including different operation modes and output power of MES device, connection locations, fault locations, and fault types. Large amounts of simulation results show that the proposed adaptive overcurrent method can overcome the underreach and overreach problems of protection scope, demonstrating its good application prospects.

Fault ride through constrained protection scheme for distribution networks with DFIG-based wind parks

• Investigate the effect of protection scheme on the FRT requirements of DFIGs. • Preventing disconnection of DFIGs by integrating FRT into overcurrent protection. • Determine least number of communication links for relays to prevent FRT violation. • Independent of DG control, applicable to different control modes during fault. The main protection of distribution networks is based on overcurrent relays (OCRs). Due to the slow operation of these relays, some distributed generations (DGs), e.g. wind parks, may be unable to meet the fault ride through (FRT) requirements, which leads to unnecessary generation loss during faults. This paper proposes a new protection scheme for distribution networks that considers the FRT requirements of DFIG-Based wind parks. This is achieved by considering both the protection coordination constraints and FRT requirements in a single protection scheme. Considering the FRT requirements, the new method determines whether each overcurrent relay operates fast enough. If not, the proposed scheme determines a suitable solution for each relay to facilitate a faster operation. The proposed method is tested on the IEEE 33 bus test network and compared with conventional methods. Its superior impact on improving the FRT requirements and hence preventing unnecessary disconnection of DFIG-Based wind parks during short circuit faults is demonstrated through simulation results, proving by this its applicability and efficacy.

Direct current distribution network protection scheme based on inductive current limiting

Converter blocking in the case of pole-to-pole short circuit of the direct current (DC) distribution network can cause large-scale power outage and slow system recovery. Given this issue, a scheme of short circuit protection between poles of the DC distribution network based on the cooperation of fault current limiting module and DC circuit breaker is proposed in this paper. According to the inductive current limiting topology, the transient characteristics of the bridge arm current and the fault current on the DC side of the converter are analyzed, and the theoretical calculation method and selection principle of the current limiting inductor parameters are given. The proposed protection scheme can realize the fault ride-through of the converter during the pole-to-pole short circuit, reduce the scope of power outage and quickly restore the system. The simulation results under the PSCAD/EMTDC environment verify the correctness and feasibility of the protection scheme.

An adaptive fault-component-based current differential protection scheme for distribution networks with inverter-based distributed generators

The high penetration of inverter-based distributed generators (IBDGs) T-connected into distribution networks has changed their structure from single-source networks to multi-source multi-branch networks; therefore, conventional distribution network protection schemes are difficult to apply. To this end, a mathematical model of IBDG fault component current considering the control strategy of IBDG is established, and then, a method for estimating the IBDG fault component current using only electrical information at both terminals of the protected line is proposed. On this basis, an adaptive fault-component-based current differential protection scheme suitable for distribution networks with IBDGs is proposed. The proposed scheme only needs to exchange the electrical information at both terminals of the protected line; that is, it can adapt to multiple IBDGs that are T-connected into the distribution networks, reducing the requirements of multi-terminal protection for communication channels and thus lowering costs. Finally, the effectiveness of the proposed protection scheme is demonstrated in the PSCAD/EMTDC software. The results show that the proposed protection scheme is not affected by the location, capacity of the IBDGs, or the fault type and has a high sensitivity.

Multi-Agent System-Based Hierarchical Protection Scheme for Distribution Networks With High Penetration of Electronically-Coupled DGs

With the increasing penetration of distributed generations, preserving the protection system coordination is of great importance for the distribution network operation. This paper presents a supplementary protection strategy for the multi-agent system (MAS)-based hierarchical protection scheme (HPS). The primary level of MAS-based HPS clears the fault and preserves the protection coordination while the higher levels update the relay settings. The key advantage of the proposed supplementary scheme is that the primary level can autonomously and quickly preserve the protection coordination when the main relay is during the time-consuming process of updating settings in the case of network operating condition change. By adopting converter-based DGs as the only MAS agents, the proposed supplementary scheme divides the distribution network into several zones that communicate together using point-to-point communication. Without communicating with higher protection levels, the supplementary protection limits the influence of DGs on the fault current by controlling the produced power of each zone. The effectiveness of the proposed strategy is validated through several simulation case studies on the Isfahan distribution network.

Pilot protection scheme for distribution network considering low voltage ride‐through of inverter‐interfaced distributed generators

According to the latest grid‐connected standard, the failure of IIDG (inverter‐interfaced distributed generator), represented by wind power and photovoltaic power, is characterized by strong nonlinear output. Therefore, the protection scheme based on the traditional fault characteristics is difficult to be applied to the distribution network with high permeability IIDG access. Based on the low voltage traversing operation characteristics of PQ control strategy IIDG, the work analyzed the distribution characteristics of positive sequence fault components in distribution network, and proposed a pilot protection scheme for distribution networks based on the comparison of current amplitudes on both sides of line. This scheme not only reduced the strict requirement of pilot protection for synchronous sampling of communication facilities, but also eliminated the influence of load current. Moreover, it had good practicability and economy without the protection and cooperation with other components. At the same time, in order to avoid the misoperation of amplitude ratio protection criterion for non‐fault line due to the existence of unmeasured load branches, the distribution characteristics of node branch current abrupt changes were used to establish the auxiliary criterion for node‐branch current mutation. It solved the action dead zone of the ratio protection criterion. Finally, the feasibility of the proposed protection principle was verified by DIgSILENT simulation. © 2020 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Research on regional centralized protection scheme for distribution network integrated with electric vehicles

In view of the difficulty in balancing between selectivity and sensitivity of current protection in distribution networks integrated with electric vehicles, a regional current protection method applicable to distribution networks with large-scale electric vehicle penetration is proposed. First, considering the effect of the converter control strategy of electric vehicle chargers, a theoretical analysis is made to determine the expression of the short circuit current that the electric vehicle charger provides when faults occur on feeders. On this basis, according to the minimum short circuit current, the current protection criterion that meets the requirement of sensitivity alone is established. And then, combining multiple start-up signals of the criterion on the fault line and multiple-level neighboring lines after fault occurs, the regional current protection scheme for distribution network is constructed. Finally, simulation tests conducted in Real-Time Digital Simulator (RTDS) of IEEE 33-bus system verify that the proposed method can effectively avoid mal-cooperation between different protection zones which is common in traditional current protection. Besides, the proposed scheme is not affected by factors such as the charging capacity of electric vehicles, the number and the location of charging facilities, etc., and can accurately identify the fault location even when the information is partly missing or in error.

A bi-level multi agent based protection scheme for distribution networks with distributed generation

This paper proposes a bi-level multi agent system-based protection scheme with the aim of maintaining the coordination of over current relays in the presence of Distributed Generation (DG) resources. In the proposed scheme, the distribution network protection has been divided into two levels so that the first level protection is implemented through relay agents which are participated in the protection scheme via exchanging information to each other. The second protection level is performed by generation agents when the fault still remains and the first level protection is not effective. To this end, the generation agents are categorized into the main and distributed zones and perform the protection through sharing information together. The effectiveness of the proposed model is examined through several simulation studies on a practical distribution network.

Ring-shaped DC Distribution Network Protection Scheme Research Based-on Voltage Prediction

In this paper, it researches the DC-ring distribution network protection scheme. Firstly, it analyzes the fault characteristics of the voltage source converter (VSC) during the DC line-to-ground. Secondly, it proposes a DC distribution network protection scheme based-on local measurement. The quadratic time-varying function is utilized to predict the line-side voltage in case of failure. The difference between the predicted voltage and the measured voltage on the line side in case of failure is utilized as the primary protective action criterion. Under voltage protection is utilized as backup protection in DC ring distribution network to guarantee safety and stability in case of failure. And the overcurrent protection is utilized as the startup criterion. The additional criteria are added to the further distinction between internal faults and external faults to prevent protection malfunction. The loop DC-distribution network protection scheme simulation based-on real-time digital simulator (RTDS) has verified the feasibility and effectiveness of the proposed scheme.

Protection Scheme of Multi-terminal Flexible DC Distribution Network Based on Current-Limiting Inductor Voltage

The rapid development of power electronic devices has promoted the rapid development of multi-terminal flexible DC distribution networks, indicating the direction of DC technology and urban power distribution systems. However, there are several technical problems in multi-terminal flexible DC distribution network that still need to be solved. In relay protection, the main difficulty faced by DC distribution network is the rapid and reliable identification of DC faults. This paper proposes a multi-terminal flexible DC distribution network protection scheme based on current-limiting inductor. First, the system configuration of the multi-terminal flexible DC distribution network is introduced. Then, the DC-side fault characteristic of the flexible DC distribution network are analysed. Based on this, a protection scheme based on current-limiting inductor voltage is proposed. Next, a complete protection scheme is designed. Finally, the proposed protection scheme is verified by real time digital simulator (RTDS). The simulation results show that the scheme is not affected by the fault resistance and fault distance.

A Virtual Multi-Terminal Current Differential Protection Scheme for Distribution Networks With Inverter-Interfaced Distributed Generators

The deployments of inverter-interfaced distributed generators (IIDGs) in medium voltage distribution networks may cause undesirable trips or tripping failures of conventional two-terminal current differential protective relays. It is economically and technically unfeasible to reconfigure large numbers of time-synchronized sampling clocks and communication channels for each terminal inside the protected zone. In this paper, a more accurate IIDG mathematical equivalent model is established that considers the control strategies of IIDG, and the profile characteristics of the positive-sequence voltage at each point of common coupling are investigated. Then, a real-time estimation algorithm is introduced for the fault current contribution of grid-connected IIDGs. On this basis, this paper proposes a novel virtual multi-terminal current differential protection scheme. This scheme only necessitates exchanging the electrical quantities between the protective relays at both terminals via an existing two-terminal pilot channel, thus reducing the cost and requirements for communications. The feasibility of the proposed protection is demonstrated in both the PSCAD/EMTDC simulation platform and the RTDS hardware experimental laboratory. A comparison of the proposed protection alongside the conventional protection is also presented. Test results indicate that the proposed protection is widely applicable to various fault conditions, thereby improving the sensitivity and selectivity of conventional protection schemes.

A Non-Standard Characteristic Based Protection Scheme for Distribution Networks

The increasing number of distributed generation (DG) units in the distribution systems poses a challenge on protection systems in terms of coordination. In addition, the single characteristic based conventional protection causes an increase in the primary operation time of the relays due to the coordination between relay pairs. As a consequence, earlier studies investigated the utilization of non-standard characteristics and protection schemes in order to ease the insufficiencies of the standard approach. However, a commonly accepted protection approach that mitigates the effect of DG while providing lower primary operating time by levering the benefits of the non-standard protection strategy has not been developed so far. In order to overcome the aforementioned drawbacks of traditional protection, this paper firstly introduces a non-standard characteristic and then proffers an unconventional protection strategy, which utilizes a double characteristic. The suggested protection approach is tested on the IEEE 14 Bus distribution system including synchronous generator based DG connection. The results show that the proposed characteristic and protection scheme are able to provide a substantial decrease in the operation time of the relays while meeting the coordination requirements.

An adaptive directional current protection scheme for distribution network with DG integration based on fault steady-state component

In view of the low reliability of traditional protection in the distribution network caused by the massive integration of DGs (distributed generation), an adaptive directional current protection scheme based on fault steady-state component is proposed in this paper. First, by analyzing the fault transient characteristics and fault equalization methods of different types of DGs, the components of system short circuit current are calculated, and the relationship between three phase components of the short circuit current is revealed. On this basis, according to the fault boundary conditions, the fault steady-state components are obtained. And then, combined with the measured voltage and measured current at the relaying point, the equivalent voltage and equivalent impedance at the backside of protection are calculated. Thus the adaptive directional current protection criteria for different fault types are formed. Simulation results demonstrate that, the proposed scheme is not affected by the type and power output of DG and the system operation mode, and could effectively prevent the protection from refusing to operate due to voltage drop.

Regional protection scheme for distribution network based on logical information

In view of the incorrect operation of local protection caused by multiple distributed generations (DGs) and branches in distribution system, a regional protection scheme for distribution network based on logical information is proposed here. Moreover, a regional centralised protection system in parallel with and independent from the existing protection system is constructed. First, the problems in local current protection of lines with multiple DGs and branches are analysed. On this basis, protection regionalisation is conducted according to the configuration of circuit breakers. Also then, by combining the start-up information of existing over-current protection set-I, set-II, and set-III, the operation criterion of regional protection is formed. Simulation tests on the IEEE 33-node distribution system verify that, the proposed scheme could accurately locate in-zone fault and block out-of-zone fault, accelerate protection operation, and shorten the outage time. Besides, the proposed criterion is fault tolerant due to redundancy in the multi-source information used. With small amount of information transmission, the requirement on information synchronisation is low.

A new coordinated backup protection scheme for distribution network containing distributed generation

This paper proposes a new backup protection scheme, named coordinated backup protection (CBP) scheme, for distribution networks containing distributed generation. The proposed protection scheme takes into account the issues faced by traditional backup protection, such as difficulty in setting parameters and complex cooperation, and considers the features of distribution networks, such as changeable power flow because of high penetration of distributed generation sources and insufficient measuring quantities. The CBP scheme includes two aspects: coordinated substation protection and regional master substation protection, who also work as nearby backup protection and remote backup protection respectively. The two protections support each other by local information coordination and regional information sharing, in order to improve the reliability of fault identification. The configuration principles and performances of the proposed backup protection scheme are addressed in the paper. Different fault conditions in the IEEE 14-node system have been used to illustrate and verify the feasibility of the CBP scheme.

Study on Relay Protection Scheme in Wind Power Integration Distribute Network

现有的继电保护系统中一般将风力发电系统作为同步发电机处理，不考虑故障下风电场提供的短路电流对继电保护的影响，但是随着大规模风电接入配电网，风力发电系统对配电网故障点提供的短路电流将会降低继电保护装置的选择性，进而导致继电保护装置的误动。为了保证继电保护满足“四性”的要求，本文通过研究分析风电接入配电网下的故障机理，提出将具有动作速度快、方向性明确、不受过渡阻抗影响的工频故障分量距离保护应用于配网的保护方案中。 Wind power generation system is generally treated as synchronous generators in the relay pro-tection system, and regardless of influence short-circuit current that provided by wind farms. But with large-scale wind power integration distribute network, the selectivity of relay protection devices is reduced by short circuit current provided by wind power generation system, which leads to the maloperation of relay protection device. In order to guarantee the relay protection to meet the requirements of the “four characteristics”, this paper, through research and analysis on wind power distribution network fault mechanism, puts forward that distance protection using power frequency fault components of voltage and current which has action speed, clear direction and not affected by the influence of transition impedance is applied to distribution network protection scheme.