Power-system protection

About: Power-system protection is a research topic. Over the lifetime, 6353 publications have been published within this topic receiving 117961 citations.

Innovative solutions for protection schemes in autonomous MV micro-grids

Abstract: In this paper the development of protection schemes for multi-phase and phase-to-ground faults in autonomous micro-grids is dealt with, accounting for the fact that a distribution “island” can be intentionally intended to operate for a long time duration (e.g. during maintenance in the main upstream network or due to economic advantages for the micro-grid electrical customers). The definition of an adequate protection scheme has to account for the extremely variable micro-grids architecture, characteristics and fault conditions that make difficult to protect them by using traditional criteria and schemes. The work aims at finding innovative protection schemes that involve minimum implementation costs for the distribution network operator. For this reason the proposed solutions make use of traditional or commercially available protective, switching and sensing devices, as well as telecontrol/automation techniques currently used in italian distribution networks. Traditional technologies employed by innovative protection schemes allow also to find interesting practical solutions to protect micro-grid feeders in presence of a high number of inverted-interfaced generators resorting to differential protection schemes. This is especially important when a micro-grid has to accommodate a large amount of generators based on renewable energy sources.

Enhanced Protection Security Using the System Integrity Protection Scheme (SIPS)

Abstract: Events, such as faults, loss of load, or generation may cause unwanted relay operations which initiate cascade tripping leading to system collapse. Security of power system protection is a major concern for utilities. A system integrated protection scheme-based approach is proposed for improving the security of protection operations. Identification of vulnerable points, which may maloperate during a stressed condition and initiation of preventive strategy, is proposed in this paper. Synchronized measurements obtained from strategic locations in the system are used for this purpose. It includes two algorithms; the first of which changes the operating characteristic of relays in accordance with system condition. The second one identifies nodes in the system where load reduction can reduce the risk of maloperation. The proposed method is tested for the New England 39-bus system and is found to be accurate.

Setting-Less Protection: Feasibility Study

Abstract: A new protection scheme is proposed that does not require settings or the settings are simple and the need to coordinate with other protective devices has been removed. The approach can be viewed as a generalization of differential protection and it is enabled with dynamic state estimation. Specifically, the proposed protection scheme is based on continuously monitoring terminal voltages and currents of the component and other possible quantities such as tap setting, temperature, etc. as appropriate for the component under protection. The monitored data are utilized in a dynamic state estimation that continuously provides the dynamic state of the component by fitting the data to the basic model equations of the device under protection. The dynamic state is then used to determine the health of the component. Tripping or no tripping is decided on the basis of the health of the component. The basic approach, the analytics and the requirements for successful implementation of this concept are presented. Numerical experiments are presented to validate the method as well as an example comparison with conventional protection. Finally an evaluation of feasibility is provided based on present day microprocessor capabilities and it is concluded that present day microprocessors do have the computational power required by the proposed approach.

A Petri-net algorithm for multiple contingencies of distribution system operation

Abstract: In this paper, a Petri net (PN) algorithm combined with a new power system restoration approach is implemented for multiple distribution contingencies. This approach is performed by releasing some loads required to maintain the rest of the system in safe operation in overload cases and opening all of the switches in the out-of-service areas for fault cases, and then closing proper switches to restore the isolated areas. PN switching models and the construction of PNs for multiple contingency operation are proposed to implement the restoration algorithm. Problem solving is efficiently performed by parallel-like reasoning in the PN for all the multiple events simultaneously. Heuristic rules and evaluation functions are presented for the best first search in the PN. Multiple contingencies studied in this paper include problems of feeder fault/overload/over-unbalance and main transformer fault/overload. A practical Taiwan power (Taipower) distribution system is simulated to demonstrate the effectiveness of the proposed method. It is concluded that multiple contingencies of distribution systems can be solved by the proposed method effectively.

Differential protection of microgrids with central protection unit support

Abstract: Deployments of Distributed Generators (DGs) have large impacts on the structure of electrical networks. In order to tackle these issues, the `Microgrid' concept has been proposed. However, due to their unprecedented structure, these smaller grids experience very significant protection issues. Conventional fault current protection schemes cannot be used and should be modified due to the existence of generators at all levels of the distribution system. Furthermore, two distinct operating modes (grid connected and islanded modes) exist in microgrids causing the fault currents in a system to vary substantially. It is also a challenge to operate Inverter Interfaced DGs (IIDGs) and estimate their fault currents. Consequently, differential current protection gains more attention for the microgrid protection. Differential protection is very versatile since it does not require prior knowledge of fault currents. The dynamic structure of the microgrids, ever-expanding networks and new deployments would require such a versatile protection. This paper presents a conceptual design of a protection system which employs a microgrid central protection unit (MCPU) to coordinate differential current protection. This system is also used to accommodate multi-terminal differential protection and propose a roll-back strategy, in case of communication failure. The proposed system is also compared with the differential protection from a reliability perspective.