E.O. Schweitzer

Bio: E.O. Schweitzer is an academic researcher from Schweitzer Engineering Laboratories. The author has contributed to research in topics: Protective relay & Fault (power engineering). The author has an hindex of 3, co-authored 3 publications receiving 150 citations.

Negative-sequence overcurrent element application and coordination in distribution protection

Abstract: Negative-sequence overcurrent elements do not respond to balanced load and can thus be set to operate faster and more sensitively than phase overcurrent elements for phase-to-phase faults It is demonstrated that on a radial distribution system negative-sequence overcurrent elements need only be coordinated with downstream phase overcurrent devices for phase-to-phase faults Coordination for other fault types is then achieved with no further analysis required The effects of negative-sequence load current and open phase conductors on negative-sequence overcurrent elements are discussed >

Predicting the optimum routine test interval for protective relays

Abstract: This paper discusses the goals of routine maintenance testing for protective relays. The paper advances a Markov probability model that predicts the optimum test interval for protective relays with and without self-testing capabilities. The model uses known system transition rates and relay failure rates. The probability model shows that the optimum test interval for a relay with self-tests is quite long. >

A new method for protection zone selection in microprocessor-based bus relays

Abstract: Use of graph theory simplifies representation of complex bus arrangements in power system stations. This paper presents a new method, based upon graph theory, for selecting bus protection zones in microprocessor-based relays. We use a typical bus arrangement to illustrate the graphical representation of station arrangements, graph operations, and associated matrix operations. We also describe an implementation of the zone selection method and use two examples to demonstrate the advantages of the method. Using the status of switching devices in the station, the zone selection method provides the relay with real-time bus arrangement information. The bus relay uses this information to assign input currents to a differential protection zone and to select which breakers to trip for a bus fault or breaker failure.

Fault Direction Estimation in Radial Distribution System Using Phase Change in Sequence Current

Abstract: When a remotely sited wind farm is connected to the utility power system through a distribution line, the overcurrent relay at the common coupling point needs a directional feature. This paper presents a method for estimating the direction of fault in such radial distribution systems using phase change in current. The difference in phase angle between the positive-sequence component of the current during fault and prefault conditions has been found to be a good indicator of the fault direction in a three-phase system. A rule base formed for the purpose decides the location of fault with respect to the relay in a distribution system. Such a strategy reduces the cost of the voltage sensor and/or connection for a protection scheme which is of relevance in emerging distributed-generation systems. The algorithm has been tested through simulation for different radial distribution systems.

Superimposed Adaptive Sequence Current Based Microgrid Protection: A New Technique

Abstract: In this paper, an adaptive directional overcurrent relaying technique based on the positive-sequence (PSQ) and negative-sequence (NSQ) superimposed currents is proposed for microgrid protection. Due to the change in mode of operation of microgrid, the level and direction of prefault current are altered. On occurrence of a fault in any line section of the microgrid, coordination between the primary and backup overcurrent relays is lost due to variations in level and direction of fault current. With inception of faults, the current contributed by the inverter-based distributed energy resource is in the range of 2 p.u. To solve protection coordination issue, this paper presents an adaptive overcurrent relay settings using PSQ and NSQ superimposed currents those are contributed during fault conditions. Further, the direction of the fault is obtained using the new phase change between prefault and superimposed sequence fault currents. The proposed technique is implemented on a dSPACE processor board, which is connected to a real-time digital simulator to carry out the hardware-in-the-loop test. Extensive simulation and hardware results obtained for several microgrid operating modes indicate the effectiveness of the proposed technique. This proposed approach is independent of the voltage information.

New Models and Concepts for Power System Reliability Evaluation Including Protection System Failures

Abstract: This paper develops new models and concepts for incorporating the effect of protection system failures into power system reliability evaluation. The two types of protection failures, i.e., undesired-tripping mode and fail-to-operate mode, and their impact on reliability modeling are discussed. A complete Markov model for current-carrying components is established and its simplified form appropriately describes the overall reliability situation of individual components. Concepts of self-down state and induced-down state are introduced and used to build the composite unit model for quantitatively assessing the influence of protection failures on modeling system states. Finally, a Markov model of power systems with protection failures is proposed for system reliability evaluation. The proposed methodology is then illustrated in detail.

Adaptive Agent-Based Wide-Area Current Differential Protection System

Abstract: 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.

Agent-based self-healing protection system

Abstract: 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.