Journal of Reliable Power - SEL

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Observations: 1. Equation 1 maps all the points on any mho circle of reach r onto a single point on the number line. If we need four mho circles, we no longer require four comparators. Instead, we simply need four tests of the calculated r. For example, a Zone 1 mho circle test might test r against 0.85, which represents a reach of 85%. Figure 4 illustrates mapping of mho circles into points for a four zone relay. 2. Because V could be zero, we cannot rely on the sign of r to reliably indicate direction. Fortunately, the denominator of the r-equation is a directional element because it tests the angle between a voltage and a current. The sign of the denominator reliably indicates fault direction. The answer is simply the intersection of three two-input comparator characteristics, using pairs (X,Y), (Y,Z), and (Z,X). This arrangement is shown in the bottom of Figure 5. Refer to the coincidence timing diagram shown in the middle of Figure 5. Assume signals X and Y are slightly less than 90° apart, so we barely produce an output if X and Y were the only two inputs. Input Z does not interfere with the output as long as its leading edge is between the leading edges of X and Y. (Assuming all pulses are 180° wide, we need not make the parallel argument about the trailing edges.) The first condition is X and Y overlap by at least 90°. The two-input comparator XY represents this condition. The second condition is that the leading edge of Z lies between the leading edges of X and Y. The ZX condition ensures that Z is within ±90° of X. The YZ condition ensures that Z is within ±90° of Y. If Z leads X, then we lose the YZ output. If Z lags Y then we lose the ZX output. Therefore Z must be between X and Y, which is the same condition we noted for the three-input comparator. X Y Z 90° 0° Output T X Y Z X Y 90° 90° Figure 4: Each Mho Circle Maps Onto a Point on the M-Line Y Z 90° 90° T III. MULTIPLE-INPUT COMPARATORS ARE REALLY A FAMILY OF TWO-INPUT COMPARATORS Multi-input comparators are widely used in distance relays. These comparators can be easily understood by representing them as several two-input comparators. The top of Figure 5 shows a three-input comparator. If inputs X, Y, and Z overlap by at least 90°, then output T asserts. What characteristic does a multiple-input comparator provide Z X 90° 90° Figure 5: Coincidence-Timing Multi-Input Logic IV. A QUICK REVIEW OF MHO ELEMENT POLARIZING CHOICES Mho elements compare the angle between (Z • I – V) and V p . There are many choices for the polarizing voltage, V p . Table 1 reviews some of them. 6 | Journal of Reliable Power
TABLE 1: MHO ELEMENT POLARIZING CHOICES Operating Polarizing Characteristic General Comments (Z • I bc – V bc ) V bc (self pol.) • No expansion • Unreliable for zero-voltage faults. • Directionally insecure for reverse bus faults during high load. Requires additional directional element. (Z • I bc – V bc ) –j • V a (cross pol. w/o memory) • Good expansion for φ–φ faults. • Unreliable for zero-voltage 3φ faults. • Reverse bus fault security problems during high load periods. Requires additional directional element. (Z • I bc – V bc ) –j • V a,mem (cross pol. w/ memory) (Z • I bc – V bc ) –j • V a1mem (pos.-seq. mem. pol.) [Z • (I) –V a ] I = I a + k • I r V a (self pol.) • Good expansion for phase faults. • Reliable operation for zero-voltage 3φ faults. • Rev. φ–φ bus fault security problems during high load periods. Requires additional directional element. • Single-pole trip applications require study for pole-open security. • Greatest characteristic expansion for φ–φ and 3φ faults. • Reliable operation for zero-voltage 3φ faults until pol. memory expires. • Rev. φ–φ bus fault security problems during high load periods. Requires additional directional element. • Best single-pole trip security. • No expansion. • Unreliable for zero voltage single-lineground faults. • Requires directional element. [Z • (I) –V a ] I = I a + k • I r j • V bc (cross pol.) • Good expansion. • Reliable operation reliable for zero-voltage single-line-ground faults. • Requires directional element. • Single-pole trip applications require study for pole-open security. [Z • (I) –V a ] I = I a + k • I r V a1mem (pos.-seq. mem. pol.) • Greatest expansion. • Reliable operation for zero-voltage ground faults. • Best single-pole trip security. Distance Relay Element Design | 7
Page 1 and 2: $12.00 Journal of Reliable Power Vo
Page 3 and 4: Journal of Reliable Power Volume 1
Page 5 and 6: Capable of running protection calcu
Page 7: Both P and Q are two-input phase an
Page 11 and 12: For an Aφ-ground fault on the syst
Page 13 and 14: The most onerous 3φ fault is one w
Page 15 and 16: If the angle is near +120°, then t
Page 17 and 18: Impedance-Based Fault Location Expe
Page 19 and 20: A. Simple Reactance Method From Fig
Page 21 and 22: Figure 9 shows a screen capture of
Page 23 and 24: The relay then performs “torque
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
Page 39 and 40: 80 60 40 20 R F 100 3 3 S 2 5 6 4 1
Page 41 and 42: 15. A POTT scheme implemented over
Page 43 and 44: Transmission Line Protection System
Page 45 and 46: One-Cycle Directional Element Figur
Page 47 and 48: element misoperation. Shunt reactor
Page 49 and 50: • SW2 is in Position 1 when there
Page 51 and 52: Complete reclosing relay supervisio
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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6 VI. ZONE 1 OVERREACH DUE TO CVT I
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8 1_VA 1_VB 1_VC 2_VA 2_VB 2_VC 3_V
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10 The phasors during the fault are
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12 The prefault data from the backu
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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
Page 87 and 88:
Hou, Daqing, and Jeff Roberts. “C
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©2010 Schweitzer Engineering Labor
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Journal of Reliable Power - SEL

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