The mechanical effects of short-circuit currents in - Montefiore

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The histograms below for the instant of occurrence leading to maximum asymmetry on the most loaded phase (here central phases n°3 and 4), the histograms 1,0 0,8 0,6 0,4 0,2 0,0 -0,2 -0,4 -0,6 -0,8 -1,0 94 below show the relative variation of loads on the other phases. Separate phases D=d Separate phases D=2d 1 2 3 4 5 6 1,0 0,8 0,6 0,4 0,2 0,0 -0,2 -0,4 -0,6 -0,8 -1,0 1 2 3 4 5 6 n (1) ~2 ~2 n (2) < 1,1 < 1,1 Figure 5.27 Relative variation of response at the maximum asymmetry 1) "short circuit" hypotheses 2) short circuit and wind combined hypotheses
The wind may act in the same direction as the electrodynamic loads. This is the case for phases 2, 4 and 6 in the above histograms. But for the other phases it acts in the opposing direction. With respect to the number of loaded elements, the cumulated risks on the various phases of the two busbars gives a mean number n per suite of loaded post insulators of less than 1.1 in the case of combined loads and of approximately 2 in the case of a simple electrodynamic hypothesis. 5.2.3.7.4. Structures with a single busbar For certain substations with only one busbar or for cross connections comprised of rigid bars, the analyses made in 5.2.3.7.2 for the fault on a single busbar can be reused. 5.2.3.7.5. Influence of connectors Another factor reduces the number of post insulators concerned, i.e., the distribution of loads between post insulators according to the type of connector. The types of connector must frequently installed are: a) successions of clamped - clamped and pinned - pinned connectors. In this case, half the post insulators (n=2) are loaded (ρ=0.5). b) successions of clamped - clamped then sliding, - sliding then pinned - pinned connectors. In this case, two-thirds of the post insulators (n=3) are loaded (ρ=0.67). c) clamped - pinned fittings which distribute loads uniformly, which means that all post insulators located relatively far from the extremities along the path of maximum currents are loaded (ρ=1). We define ρ as: (5.24) ρ = 1 n = 2ou3 n= 2 ou 3 ∑ n= 1 Risk( F / F ) Risk( F / F ) 0 n R The set (Fn) corresponds to the loads on the post insulators of the most loaded busbar (longitudinal variation of load), but limited in size to two or three elements defined in paragraphs a) and b). 5.2.3.7.6. Common mode faults A distinction must be made between a substation and a family of substations. In the case of one substation, there may be common mode faults such as those resulting from component manufacture or assembly. Example: On a given substation, it is very likely that many of the ceramic post insulators come from the same production batch. This may give rise to statistically above-average or below-average strength. In short, for the analysis of a family of substations, the advantages of the probabilistic approach are clearly apparent. R 95 5.2.3.7.7. Conclusions For N sequences on a section of busbars, we thus take . ρ . post insulators subject to maximum loads. n N 5.2.3.8 FAILURE RECURRENCE TIME 5.2.3.8.1. Risk at a substation For line fault The overall maximum risk at a substation is given by the expression: (5.25) R l n N Risk F L o P = νλη . . . P. . ρ. . ( ) F with ν : normal operating rate of fault elimination (close to 1). λ : number of faults on overhead lines connected per km and per year, η : rate of high-amplitude polyphase faults (hence nonresistive), lP : cumulative length of the risk zone in km, n : number of loaded post insulators per busbar suite, ρ : coefficient depending on the type of connector N : suite number, Example: For λ=20x10 -2 per km and per year, η=30%, l=6km, n =1,5 ρ=1, N=14 suites, Risk Fo R ( )= 10 FR -5 , there is thus a probability of substation failure of around 7.6 10 - 5 , corresponding to a recurrence time of more than 13000 years for a safety factor of 0.7. For line fault in the event of failure The previous analysis is also applicable in the event of failure (circuit breakers or protection devices), though the elimination times may be different and the resulting loads increased. It is important to determine the amplitude of loads amplification, in view of the remarks made in section 5.2.3.1.4 on the effect of saturation when the clearance time exceeds the mechanical reaction time. In (5.25), Fo is replaced by F1 and the failure rate: ν : (protection system and/or circuit breaker failure rate) is taken into account. The increase in risk is often low and the reduction in the failure rate means that this term can be ignored. For substation fault The maximum overall risk at a substation is given by the expression: R n N Risk F P o P = λη . . . ρ. . ( ) with F λ : annual frequency of faults in the substation, η : rate of high-amplitude non-resistive polyphase faults (for example, accidental earthing with all available network power). R
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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
Page 43 and 44: movement of the dropper (swing out
Page 45 and 46: This value has to be compared with
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Page 49 and 50: a) b) c) 3 m 2 1 0 -1 δ m δ 1 Mov
Page 51 and 52: Droppers with fixed upper ends Duri
Page 53 and 54: Manuzio developed a simplified meth
Page 55 and 56: From prior tests the stiffness valu
Page 57 and 58: Force / kN Force / kN 100mm 200mm 4
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Page 61 and 62: 3.7. SPECIAL PROBLEMS 3.7.1. Auto-r
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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 = ∫
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Page 80 and 81: 5.2.2. A global Approach For analyz
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Page 84 and 85: 5.2.3.1.7. Proposed Approach The st
Page 86 and 87: The first case (Figure 5.14) corres
Page 88 and 89: centers are normally balanced by ba
Page 90 and 91: Remark: The risk integral (5.3) can
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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 114 and 115: Figure 8.2 What is ESL in this case
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 .
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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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