Journal of Reliable Power - SEL

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1) Estimating and Comparing Fault Resistances Solves the Problem When the angle itself is not conclusive, e.g., when the angle is more than 30° from its expected value, we can compare phase and ground fault resistance estimates, and select the fault type associated with the minimum resistance. For example, and again referring to the bottom of Figure 16, a comparison of an estimate of Rbg against the minimum phaseto-phase fault resistance (in this case, Rbc), would reveal that Rbg is much larger than Rbc. Therefore, the logic concludes the fault mainly involves phases B and C, and the best measurement is made by the BC element. IX. SUMMARY Important points presented in this paper include: 1. A review of several types of phase-angle comparators shows their similarities and differences. 2. A multiple-input comparator can be viewed as a family of two-input comparators, which includes every pair of inputs. 3. Writing the torque equation for a relay characteristic, setting it equal to zero, and solving for a scalar multiple of the element reach yields a result which maps points on the characteristic onto a single point on the number line. This makes for very efficient synthesis of a family of characteristics with different reaches. 4. Positive-sequence memory potential is generally the most secure and reliable polarization method for mho characteristics. 5. A negative-sequence element which calculates negative-sequence impedance, and tests it against thresholds is presented. It is easy to adapt to virtually any system conditions, because its two threshold settings relate to system impedances. 6. We present ground-fault-resistance elements for quadrilateral characteristics, which estimate the fault resistance, and use the fault-current estimate 1.5 • (I0 + I2). This estimate rejects the loadinfluenced positive-sequence current, but includes the rest of the fault current. 7. A negative-sequence directional check is sufficient to overcome security problems with phase and ground distance elements for unbalanced faults. 8. A positive-sequence directional element can be used to cut off part of the mho characteristics in the second quadrant of the impedance plane, to enhance security for three-phase faults. This element would normally be set with a maximum torque angle much less than that of the mho circle. 9. Instead of shaping impedance-plane tripping characteristics to avoid load, we introduced a load characteristic. Impedances must leave the load characteristic, before tripping is permitted for threephase faults. The load characteristic looks like a bowtie without the knot, and therefore neatly surrounds load areas. It minimizes the area of the impedance plane eliminated for load considerations. 10. We point out a potential problem with fault-type selectors based on the angle between I0 and I2. They may err for certain resistive LLG faults. The solution is a comparison of estimates of LL and LG fault resistances. X. REFERENCES [1] R.J. Martilla, “Directional Characteristics of Distance Relay Mho Elements: Part II - Results.” IEEE Trans-actions on Power Apparatus and Systems, Vol. PAS-100, No.1 January 1981. [2] Edmund O. Schweitzer III, “New Developments in Distance Relay Polarization and Fault Type Selection,” 16th Annual Western Protective Relay Conference, October 24 - 26, 1989, Spokane, WA. [3] A.R. Van C. Warrington, “Protective Relays: Their Theory and Practice.” Chapman and Hall, 1969, Volume I and II. XI. BIOGRAPHIES Edmund O. Schweitzer, III received BSEE and MSEE degrees from Purdue University in 1968 and 1971, respectively. He earned a PhD at Washington State University (WSU) in 1977.His professional experience includes electrical engineering work at Probe Systems in California and the National Security Agency in Maryland. He served as an assistant professor at Ohio University and as an assistant and an associate professor at WSU. Since 1983, he has directed the activities of Schweitzer Engineering Laboratories, Inc. (SEL), the company he founded in Pullman, Washington. SEL designs, manufactures, and markets digital protective relays for power system protection. Schweitzer started investigating digital relays during PhD studies at WSU in 1976, which produced both his doctoral dissertation and SEL. His university research was supported by Bonneville Power Administration, Electric Power Research Institute, and various utilities. Although the company has grown significantly, Schweitzer is still involved in the development of new relays and auxiliary equipment. He is a Fellow of the Institute of Electrical and Electronic Engineers (IEEE), is a member of Eta Kappa Nu and Tau Beta Pi, and has authored or coauthored 30 technical papers. Jeff B. Roberts received his BSEE from Washington State University in 1985. He worked for Pacific Gas and Electric Company as a relay protection engineer for over three years. In November, 1988 he joined Schweitzer Engineering Laboratories, Inc. as an Application Engineer. He now serves as Application Engineering Supervisor. He has delivered papers at the Western Protective Relay Conference, Texas A&M University and the Southern African Conference on Power System Protection. He holds one patent on the SEL-121B relay and has other patents pending. Copyright © SEL 1992, 1993 (All rights reserved.) Printed in USA Rev. 2 14 | Journal of Reliable Power
Impedance-Based Fault Location Experience Karl Zimmerman and David Costello, Schweitzer Engineering Laboratories, Inc. I. INTRODUCTION Accurate fault location reduces operating costs by avoiding lengthy and expensive patrols. Accurate fault location expedites repairs and restoration of lines, ultimately reducing revenue loss caused by outages. In this paper, we describe one- and two-ended impedancebased fault location experiences. We define terms associated with fault location, and describe several impedance-based methods of fault location (simple reactance, Takagi, zerosequence current with angle correction, and two-ended negative-sequence). We examine several system faults and analyze the performance of the fault locators given possible sources of error (short fault window, nonhomogeneous system, incorrect fault type selection, etc.). Finally, we show the laboratory testing results of a twoended method, where we automatically extracted a two-ended fault location estimate from a single end. II. FAULT LOCATION METHODS AND DEFINITIONS Several methods of estimating fault location are presently used in the field: • DFR and short circuit data match • Traveling wave methods • Impedance-based methods − One-ended methods without using source impedance data (simple reactance, Takagi) − One-ended methods using source impedance data • Two-ended methods In this paper, we focus on certain impedance-based fault location methods and provide results from actual system faults. III. NOTABLE IEEE DEFINITIONS IEEE PC37.114, “Draft Guide for Determining Fault Location on AC Transmission and Distribution Lines”[1] was recently balloted and is in the approval process. One of the important contributions of the guide is the definitions section. Here are a few notable definitions found in the guide: Fault location error: Percentage error in fault location estimate based on the total line length: e (error) = (instrument reading – exact distance to the fault) / total line length. For example, suppose a line is 100 miles long and the actual fault is 90 miles from the local terminal. If the local fault locator provides a fault location of 94 miles, the fault location error is (94–90)/100 = 4%. If the remote fault locator indicates 8 miles, the fault location error is (8–10)/100 = 2%. Homogeneous line: A transmission line where impedance is distributed uniformly on the whole length. Examples of this are lines that use the same conductor size and construction throughout. Lines that are nonhomogeneous can be a source of error for one- or two-ended impedancebased fault location methods. Homogeneous system: A transmission system where the local and remote source impedances have the same system angle as the line impedance. A homogeneous system is shown in Figure 1. Z Z Figure 1 1S 0S Z 1S = 2∠80° = 3 • Z 1S Relay mZ 2L Z Z 1L 0L R F (1-m)Z 2L = 8∠80° = 3• Z Example of a Homogeneous System 1L Relay ∠Z ∠Z 1R 0R Z 1R = ∠Z 1S = ∠Z Nomograph: A graph that plots measured fault location versus actual fault location by compensating for known system errors. Figure 2 shows a 69 kV line with 12.47 kV underbuild. Figure 2 Relay Location N 69 kV Line Configuration Sketch N 69 kV 0S 12.47 kV Load How to build a nomograph: 1. Calculate line constants. 2. Determine which faults require a nomograph. 3. Using short circuit program, apply faults along the length of line (10%, 20%, etc.). 4. Plug resultant voltage and current values into fault location algorithms. 5. Plot a short circuit (actual) vs. calculated (relay) fault location. Impedance-Based Fault Location Experience | 15
Page 1 and 2: $12.00 Journal of Reliable Power Vo
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Page 7 and 8: Both P and Q are two-input phase an
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Page 11 and 12: For an Aφ-ground fault on the syst
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Page 25 and 26: IX. LAB TEST SETUP Several line fau
Page 27 and 28: APPENDIX The following are the rela
Page 29 and 30: The following shows the analog math
Page 31 and 32: Digital Communications for Power Sy
Page 33 and 34: increasing security by a factor of
Page 35 and 36: The receiver amplifier is the major
Page 37 and 38: Noise from faults or other sources
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Page 41 and 42: 15. A POTT scheme implemented over
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Page 45 and 46: One-Cycle Directional Element Figur
Page 47 and 48: element misoperation. Shunt reactor
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Page 53 and 54: IX. BIOGRAPHIES Armando Guzmán, P.
Page 55 and 56: 2 II. COMMON ZONE TIMING In June 20
Page 57 and 58: 4 ment 67N2 after a 1-cycle carrier
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1 Adaptive Phase and Ground Quadril
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3 C. Short Line Applications A shor
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5 II. QUADRILATERAL DISTANCE ELEMEN
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7 For the purpose of implementing t
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9 The three-phase fault detection e
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11 Zone 1 distance elements should
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13 Fig. 24 shows the apparent resis
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15 B. Adaptive Resistance Element F
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17 Fig. 34 and Fig. 35 illustrate t
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Line Protection Bibliography Issue
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Hou, Daqing, and Jeff Roberts. “C
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©2010 Schweitzer Engineering Labor
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