Articulo

448

IEEE Transactions on Power Systems, Vol. 11, No. 1, February 1996

DESIGN, IMPLEMENTATION AND PERFQRMANCE EVALUATION OF A NEW DIGITAL DISTANCE RELAYING ALGORITHM
D.L. Waikar, MIEEE Dept. of Electrical Engineering Singapore Polytechnic, Singapore

A.C. Liew, Sr. MIEEE, S. Elangovan, Sr. MIEEE
Dept. of Electrical Engineering National University of Singapore, Singapore
This paperpresents the design, simulation, implementation and performance evaluation of a new computationally efficient and accurate digital distance relaying algorithm [IS]. Performance of the simulated relay was evaluated in three phases. Published historical data were used in the first phase for validation purpose. The second phase used voltage and current signals generated by ATP and a sample power systemfor various fxst, second and third zone faults. Voltage and current waveforms and performance indices such as fault impedance estimates and trip speed were formulated and plotted to examine the response of the relay software. In the third phase, a prototype of the relay was developed using a low-cost general purpose high speed microcontroller, signal acquisition and conditioning components andassembly language based software. The prototype was tested using real-time fault data generated from physical models of the transmission lines. Results of these performance evaluation studies are reported in this paper.

ABSTRACT This paper presents the design, simulation, implementation and performance evaluation of a computationally efficient and accurate digital distance relaying algorithm.Published historical data were used in the first phase for validation purpose. Sample results illustrating highly accurate fault impedance estimates for various conditions are reported. The second phase uses voltage and current signals generated by Alternative Transients Program (ATP) and a sample power system for various first-zone, second-zone and third-zone faults. Results of these studies confumingstabifity and computational efficiency of the algorithm are presented a and discussed. In the third phase, a prototype of the relay w s developed and tested using real-time fault data generated from physical models of the transmission lines. Oscillographs for these conditions were recorded. Results of these tests indicating high speed relay operation are also discussed. The performance evaluationstudies reported in this paper conclusively demonstrate that the new algorithm provides fast and accurate fault impedance estimates for the three-zone protection of transmission lines.

Key words: performance evaluation, digital distance relay

1. INTRODUCTION
Recently, digital distance relays have been applied for the protection of power transmission lines [l]. Typical digital distancerelays receive voltage and current signals from signal acquisition units [Z]. These signals are then conditioned and provided to the relay software [l-31. Various algorithms and methods such as fault detection, phasor estimation, fault classification, sequence component calculation and appmnt impedance estimation are then implemented in the relay software [4-181. The estimated fault impedance isevaluated in the relay characteristic [19] for making trip decisions. Digital distance relays, therefore, need fast and accurate fault impedance estimating algorithms for high speed and secure decision making.

A new digital distance relaying algorithm proposed by the authors uses the phasor estimates, sequence components of pbasors and fault classification scheme before calculating fault distance.Figure 1 depicts a power transmission network experiencing a fault at B.

-L
ZX

-x

--

L

f

ZOH L1H
*f

se

z 2H

Figure 1:

A sample power system used in the performance evaluation of the new algorithm 1151.

Positive, negative and zero sequence networks of the system experiencing the fault from the relay located near bus P and various shunt fault conditions were used...