Current differential protection relays are widely applied to the protection of electrical plant due to their simplicity, sensitivity and stability for internal and external faults. The proposed idea has the feature of unit protection relays to protect large power transmission grids based on phasor measurement units. The principle of the protection scheme depends on comparing positive sequence voltage magnitudes at each bus during fault conditions inside a system protection center to detect the nearest bus to the fault. Then the absolute differences of positive sequence current angles are compared for all lines connecting to this bus to detect the faulted line. The new technique depends on synchronized phasor measuring technology with high speed communication system and time transfer GPS system. The simulation of the interconnecting system is applied on 500 kV Egyptian network using Matlab Simulink. The new technique can successfully distinguish between internal and external faults for interconnected lines. The new protection scheme works as unit protection system for long transmission lines. The time of fault detection is estimated by 5 msec for all fault conditions and the relay is evaluated as a back up relay based on the communication speed for data transferring.

A Novel Back Up Wide Area Protection Technique for Power Transmission Grids Using Phasor Measurement Unit

This paper proposes a multiagent-based adaptive wide-area current differential protection system. A power grid is divided into primary and backup protection zones dynamically online with the help of a developed expert system, and the relay agents of these zones cooperate to perform a differential relaying function. Predictive self-healing strategies have been proposed to prevent misoperation of the relay agent, and the communication system has been simulated. The performance of the proposed adaptive wide-area current differential protection system based on computer simulation is presented in this paper.

Adaptive Agent-Based Wide-Area Current Differential Protection System

This paper proposes an agent-based paradigm for self-healing protection systems. Numerical relays implemented with intelligent electronic devices are designed as a relay agent to perform a protective relaying function in cooperation with other relay agents. A graph-theory-based expert system, which can be integrated with supervisory control and a data acquisition system, has been developed to divide the power grid into primary and backup protection zones online and all relay agents are assigned to specific zones according to system topological configuration. In order to facilitate a more robust, less vulnerable protection system, predictive and corrective self-healing strategies are implemented as guideline regulations of the relay agent, and the relay agents within the same protection zone communicate and cooperate to detect, locate, and trip fault precisely with primary and backup protection. Performance of the proposed protection system has been simulated with cascading fault, failures in communication and protection units, and compared with a coordinated directional overcurrent protection system.

Agent-based self-healing protection system

A novel wide area backup protection algorithm to identify fault branch based on the fault steady state component is proposed. Under normal conditions of the power system, subsets of buses called protection correlation regions (PCRs) are formed on the basis of the network topology and phasor measurement unit (PMU) placement. After the fault occurs, by analyzing the fault steady state component of differential current in each PCR, the fault correlation region is confirmed and then a fault correlation factor (FCF), is calculated in real time to locate the fault branch. The simulation results for the 10-generator 39-bus system verify that this method is able to easily identify fault branch with limited measurement points.

A Fault Steady State Component-Based Wide Area Backup Protection Algorithm

This paper elaborates a new protection scheme based on dual-setting DOCRs for automated distribution networks. In this course, the reduction in relays operation time saturates as the number of these relays increases. Thus, optimal deployment of dual-setting DOCRs should be specified in an efficient manner. To do so, a multiobjective optimization approach is established, which compromises the reduction of total operation time and the number of dual-setting DOCRs. Coordination constraints are accommodated and nonstandard inverse-time characteristics are established to intensify flexibility of the proposed strategy. The proposed model lies within a nonlinear programming fashion, which is tackled by particle swarm optimization. Moreover, the augmented $\varepsilon $ -constraint approach is utilized to reach the Pareto-optimal solutions following which the fuzzy decision making process determines the best compromised solution. Detailed simulation studies are carried out to interrogate performance of the proposed approach.

Dual-Setting Directional Overcurrent Relays for Protecting Automated Distribution Networks

As power systems grow larger, it is becoming difficult to achieve reach and time coordination in backup protection when using distance relays. To cope with those problems, current differential backup protection for a busbar and transmission circuits connected to that busbar on an inter-station or wide-area basis is proposed. The proposed system can operate better than conventional systems with respect to operation time, section selectivity, etc. A system configuration is also proposed to utilize ATM transmission networks and time synchronous systems which make the construction and operation of the proposed wide-area protection system easy and flexible.

Wide-area current differential backup protection employing broadband communications and time transfer systems

Based on the authors' previously proposed wide-area current differential backup protection utilizing broadband packet communications and time synchronous systems for achieving better selectivity, smaller outage areas and faster operation times than conventional distance backup protection, experimental microprocessor-based protection devices have been examined with respect to both telecommunication and protection functions The experimental wide-area protection system consists of one central equipment (CE) unit and three terminal equipment (TE) units connected by a 155-Mbps ATM backbone network with a LAN interface and GPS time acquisition and features a simplified and effective method for expanding protection zones after primary or minimum-zone protection operation In an AC power system simulator configuring a busbar and a power line, each TE at a circuit breaker location transmits sampled current data to the CE and receives a tripping command initiated by it, and operate satisfactorily in various states of power system and telecommunications

M. Inukai

Papers

Wide-area current differential backup protection employing broadband communications and time transfer systems

Experimental examination of wide-area current differential backup protection employing broadband communications and time transfer systems