The Design And Application On Protection In Digital Substation

With the development of digital substation technology, sampled value and status information can be transmitted through optical fibers, and shared within the substation. Therefore, digital substation provides conditions for the study of integrated protection. Accordingly, this paper proposes a scheme for integrated protection, and mainly describes a method of real-time database modeling for integrated protection.The application of IEC61850 and non-conventional instrument transformers(NCIT) brings a new era in the development of substation. The protection intelligent electronic device(IED) in digital substation receives sampled data from different digital data sources(DDS) with digital interface based on IEC 61850-9-2 process bus. The mismatch in sampling rate between protection IED algorithms and different DDSs requires resampling in the protection IED to make sure the protection and other algorithms can run correctly. In this paper, a smart digital resampling scheme based on oversampling interpolator and quasi-continuous interpolator for fully digital relay protection is proposed. A computationally optimal poly-phase implementation structure and nyquist filter for the oversampling interpolator is designed and the Lagrange interpolation algorithm is chosen to approximate the impulse response of the quasi-continuous interpolator considering the reduction in error. Simulation results based on ATP/EMTD and MATLAB demonstrated the effectiveness of the proposed approach.With the With the breakthrough of electrooptical technology research on sensor application, the promulgation of IEC 61850, the application of Ethernet communication technology and the development of intelligent breaker, digital substation has become the mainstream of substation automation technology development in future. This paper briefly discusses issues related to electric energy measurement in digital substation, including the differences between electric energy measurement in digital substation and conventional substation, the impact to energy measurement of electronic transformer’s application. Meanwhile, aiming at the present issues, potential research fields of electric energy measurement in future digital substation is proposed as well.Protective relay is designed to make a trip decision based on calculation of collected measurements, and thus, the quality of data plays an important role in ensuring the reliability of protective relay. However, abnormity of any part of the data acquisition system(DAS), especially cyber risk, may make the protection system receive fake measurements and misoperate. Besides those efforts spent on the reliability of DAS and cyber security, protective relay itself should be able to tolerate fake measurements and actively minimise the impacts associated with bad data. Based on evidence theory, this study proposes an approach taking advantage of abundant information in digital substations to identify fake measurements and avoid misoperation of protective relay. When protective relay is prone to misoperate after the analysis of fake measurements from several current transformers(CTs) or voltage transformers(VTs), measurements from other CTs /VTs are rapidly collected to indicate whether there is a real fault in the power system. In this way, misoperation because of fake measurements can be prevented and CTs /VTs providing bad data can also be identified. Simulation tests demonstrate the effectiveness of the proposed approach.