A New Method for Phasor Estimation in Numerical Protective Relays Based on Generalized Delayed Signal Cancelation Filtering Roberto F. D. Filho, Francisco A. S. Neves, Maherbson A. C. Arcanjo and Marcelo C. Cavalcanti Power Electronics and Drives Group - GEPAE Federal University of Pernambuco - Recife/PE, Brazil diasrob@gmail.com, fneves@ufpe.br, maherbson@yahoo.com.br and marcelo.cavalcanti@ufpe.br Abstract—This work presents a novel phasor estimation al- gorithm based on the Generalized Delayed Signal Cancelation (GDSC) method, for estimating phasors in numerical protective relays. The method implementation requires the space-vector concept, the Clarke (αβ0) transform, and by means of a discrete- time formulation and few arithmetic operations, pre-determined undesirable sequence component harmonics are canceled, ex- tracting the sequence fundamental-frequency or harmonic com- ponents, which are required for numerical protective devices algorithms. The proposed algorithm for phasor estimation is applied for implementing a distance relay. The proposed and traditional algorithms are compared by using recorded fault data of a real power system. Index Terms—discrete Fourier transform (DFT), space vector discrete fourier transform (SVFT). I. I NTRODUCTION Protection of electrical power system is a necessary task to guarantee availability of energy to consumers. Disturbances in the power system may cause severe deviations in the operation conditions from the steady-state and provoke interruptions in the power supply. Protective relays are devices used to monitor such disturbances and, if necessary, open only the circuit breakers for interrupting the fault currents and keeping the rest of the system free from the consequences of the short-circuit currents and related damages caused by them. Unlike the conventional relays (electromechanical and static), modern relays are multi-functional devices, containing most of the available protection functions, telecommunication capability and control/automation logic design in the same housing. They are really considered intelligent electronic de- vices (IED), all this thanks to embedded digital electronics. Numerical relays are new developments of first computer relays with digital signal processing (DSP) optimized for real time performance. In order to accomplish its functions, a protection relay must distinguish the type of the fault (which phases are involved) and also determine the exact component of the power system to be isolated. For this it is usually necessary to evaluate se- quence components and/or harmonic components of the three- The authors would like to thank Conselho Nacional de Desenvolvimento Cientfico e Tecnolgico - CNPq and Coordenao de Aperfeioamento de Pessoal de Nvel Superior - CAPES, Brazil, for the financial support. phase voltages and currents separately. Accuracy in estimating phasors is then a very important task of a protection relay to ensure, for example, it is responding to the fundamental frequency components of both currents and voltages and not to high frequency components generated during a switching transient or inrush phenomenon. Further, the phasor estimation must be fast for minimizing the consequences of the fault to the power system This paper proposes the use of the generalized delayed signal cancelation method (GDSC) for obtaining the posi- tive, negative or zero sequence components at fundamental- frequency (or any harmonic frequency) of a three-phase voltage or current in numerical relays. The performance of the GDSC method is compared to discrete-Fourier transform (DFT) based algorithms in terms of accuracy and response time. Case tests based on simulated three-phase signals and also using actual recorded fault voltages and currents are presented. II. A NOVEL PHASOR ESTIMATION METHOD FOR NUMERICAL PROTECTIVE RELAYS This paper presents an application of a technique originally proposed for grid-connected power electronic converters, usu- ally used in renewable generation systems, active power filters and uninterruptible power supplies (UPS). The GDSC uses a space-vector formulation for providing, by means some stages, filtering of undesirable components of three-phase signals, as presented in [4], [5]. Although GDSC has a frequency adaptive version only the non-adaptive version is applied in this paper, for providing a comparison with the DFT-based method. A. Space-Vector Formulation A space-vector (SV) is a complex time-dependent repre- sentation of a polyphase system expressed in an orthogonal reference frame. In practice, the application of the Clarke transformation, as referred in [1], to the instantaneous phase values of a three-phase signal results in such vectorial quantity that represents, together with a homopolar component, any generic three-phase quantity. Fig. (2) shows the discussed concept graphically.