The mechanical effects of short-circuit currents in - Montefiore

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Figure 8.2 What is ESL in this case : Assume that F(t) is the tension in the cable connecting the equipment to another one or to another flexible connection. F(t) could result from the following effects 1) from pinch effect (if the connection is a bundle), 2) from swing out or falling down loads (horizontal connection between two equipment), 3) from dropper stretch (if the equipment is connected to another level with flexible connection). In the case shown, effect of F(t) and bending moment at the bottom of the equipment is completely different, it means that the inertial forces have clearly some action. The design value is the maximum bending moment at the bottom. We could have had the same M max by applying ESL instead of F(t).at the top of the equipments. The situation could have been more complex if M max had not occurred at the bottom of the apparatus. How to apply the simplified method The problem is to define the cantilever strength needed for such equipment. Figure 8.3 Laborelec 150 kV test structure for two-phase fault (Belgium). We have extracted from CIGRE brochure N’105, second part, the case 5 tested in Belgium, for which we have access to both tension in the cable and 114 1) evaluate Ft, Ff and Fpi by IEC simplified method 2) search first eigenfrequency of the equipment (if not known, use curve given in chapter 1), 3) evaluate ESL using synthetic curve given in chapter 3 (one curve for interphase effects, another curve for pinch effect), for example ESL1 = max(Ft-Fst, Ff-Fst) x ESL factor(interphase effect) and ESL2 = (Fpi-Fst) x ESL factor (pinch). Then consider max (ESL1, ESL2) = ESL 4) In case of initial static loading (Fst), just add Fst to ESL and compare total value to cantilever strength of the equipment. Remark : If you have access to advanced calculation method, you simply evaluate the dynamic response and locate maximum dynamic bending moment in the support, that bending is converted in equivalent top static load, which is compared to the cantilever breaking load. No need of ESL theory in that case. b) On support structures bending moment at the bottom of the support structures.
Figure 8.4 East cable tension evolution and bending moment at the bottom of west pole of the gantry Figure 8.5 West cable tension evolution and bending moment at the bottom of west pole of the gantry What is ESL in this case F(t) is the tension of the cable (the two left curves in Figure 8.4 and Figure 8.5). F(t) contains swing out and falling down loads (no pinch because it was a single conductor). Fmax = 8000 N(east) and 9500 N(west). These are measured values. Advanced calculation methods would have given very similar results. IEC simplified method would have given identical results for both phases, more close to west cable values of F t and F f values (because dropper influence is less on that phase). Obviously, measured values or advanced calculation values do not need any further analysis, because they give access directly to the design values, which are bending moment in the portal. Nevertheless it is of some interest to evaluate on an actual basis if any dynamic effect occurred. This can be done by the exact evaluation of ESL factor as obtained during real test measurements : 1) the maximum peak dynamic load is 8000 (east) +9500 (west) = 17500 N. (in this simplified method the fact that both load are not occurring simultaneously is neglected). 115 2) as initial static load is Fst = 2560 N in each phase, the relative increase is 17500 – 2x2560 = 12400 N 3) the ESL determined from the bending moment is (50000-15400)/6 = 5800 N (east) and (70000- 15400)/6 = 9100 N for each phase, this means a global value of 14900 N (6 is in meters and represent the height of the portal) ESL factor = 14900/12400 = 1,2. This is an exact value determined from test measurement. The dynamic effect corresponds to a 20% increase of the actual stress in the portal. Evaluation of the same ESL factor for different tests on the same structure but with different conductors (case 4 in brochure 105 f.e.) gave a factor in between 0.8 and 1.4 . How to apply the simplified method The use of the simplified method in this case would have given the following values : IEC 60865 evaluation of Ft and Ff is given in Ref 2.
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THE MECHANICAL EFFECTS OF SHORT-CIR
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3.7. Special problems .............
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1. INTRODUCTION 1.1. GENERAL PRESEN
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The pinch (first maximum) can be ve
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1.3.3.2 Supporting structures Simil
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This method allows to state the sho
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and becomes the static force in equ
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(2.26) M el-pl ⎡ y d/ 2 y = 2⎢
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V σ 3 2,5 2 1,5 1 mechanical reson
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V F 3 2,5 2 1,5 1 mechanical resona
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1. eigenmode 2. eigenmode 3. eigenm
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(2.43) U E max max = 1 2 1 = 2 l
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m (2.47) M = σm = Z mσ m dm 2 J w
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profiles in Figure 2.14 it follows
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(2.71) 2 tube tube 4 tube U ∂U
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2.3.2. Influence of two busbars a)
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Asymmetrical associated-phase layou
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d)Methods used IEC 60865 method : -
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Section 3.4 deals with the effects
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In Figure 3.5 to Figure 3.8, the ma
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Figure 3.17 Comparison calculated a
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movement of the dropper (swing out
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This value has to be compared with
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EN 60865-1 [Ref 3] with the assumpt
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a) b) c) 3 m 2 1 0 -1 δ m δ 1 Mov
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Droppers with fixed upper ends Duri
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Manuzio developed a simplified meth
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From prior tests the stiffness valu
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Force / kN Force / kN 100mm 200mm 4
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1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 ESL F
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3.7. SPECIAL PROBLEMS 3.7.1. Auto-r
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Page 65 and 66: Zug-/Druck-Kraft in kN Z eit in s F
Page 67 and 68: The numerical resolution of these e
Page 69 and 70: 4. GUIDELINES FOR DESIGN AND UPRATI
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Page 73 and 74: 5. PROBABILISTIC APPROACH TO SHORT-
Page 75: f G f(L) Lt Ls 75 G(L) ∞ R = ∫
Page 78 and 79: Only the lowest break values are im
Page 80 and 81: 5.2.2. A global Approach For analyz
Page 82 and 83: to multinode operation can compared
Page 84 and 85: 5.2.3.1.7. Proposed Approach The st
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Page 88 and 89: centers are normally balanced by ba
Page 90 and 91: Remark: The risk integral (5.3) can
Page 92 and 93: 1,0 0,8 0,6 0,4 0,2 0,0 -0,2 -0,4 -
Page 94 and 95: The histograms below for the instan
Page 96 and 97: 5.2.3.8.2. Reliability based design
Page 98 and 99: power converter in a three phase br
Page 100 and 101: The time functions of the currents
Page 102 and 103: a) Determination of the linear mome
Page 104 and 105: Figure 6.11 Coefficients mJs1 and m
Page 106 and 107: 7. REFERENCES Ref 1. IEC TC 73/CIGR
Page 108 and 109: Ref 42. Stein, N.; Miri, A.M.; Meye
Page 110 and 111: Ref 80. Fiabilité des structures d
Page 112 and 113: 8. ANNEX 8.1. THE EQUIVALENT STATIC
Page 116 and 117: As the eigenfrequency of the portal
Page 118 and 119: Figure 8.9 Case 3 (third eigenfrequ
Page 120 and 121: Both cases have the same 200-kV-arr
Page 122 and 123: a) c) 5 +25 % 0 % 4 3 F c / F st 2
Page 124 and 125: a) b) 24 kN 20 +25 % 0 % 2,0 m F c
Page 126 and 127: Case *11 (EDF 1990) This is the 102
Page 128 and 129: 8.4. INFLUENCE OF THE RECLOSURE The
Page 130 and 131: ( ( δ ) ( δ ) ) T = Mg08 . b r .
Page 132 and 133: IEC 60865 Calculations If the clear
Page 134 and 135: 8.6.1.1 With calculation of the rel
Page 136 and 137: f) Calculation of the stresses due
Page 138 and 139: d) Determination of the forces at t
Page 140 and 141: 8.7. ERRATA TO BROCHURE NO 105 In V
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The mechanical effects of short-circuit currents in - Montefiore

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