The mechanical effects of short-circuit currents in - Montefiore

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Figure 8.9 Case 3 (third eigenfrequency of 50 Hz). Curve : a) is the top displacement of the insulator (m) b) is the bottom bending moment (N.m) c). is the applied top load in N - There is a 3 Hz oscillation of the beam. - The maximum displacement at the top is around 150 mm at around 0,13 s. - Bending moment is in phase with the top displacement but has a clear presence of 50 Hz component ESL factor can easily be determined : Max bending moment around 7500 N.m (means ESL = 6500/3.8 = 1980 N) Max dynamic load value (not at the same time as the max bending) : around 3500 N ESL factor = 0.6 Time/s Time/s Time/s 118
8.3. COMPARISON OF TEST RESULTS AND CALCULATION ACCORDING TO IEC PUBLICATION 60865-1 Because of the very high complexity of the matter, CIGRE SC 23 WG 03, IEC TC 73 and DKE UK 121.2 (VDE 0103) introduced new calculation rules for so far uncovered particular arrangements only under the condition that sufficient evidence from test results was available. In spite of this time and cost consuming, quite a satisfactory number of rigid as well as stranded conductor arrangements have been made accessible to standardised calculation procedure for short-circuit stresses and strength. It is only natural that the more complex the matter gets, the more experimental and analytical efforts are required to cover new areas of calculation. To understand the effects and the physics caused by the short-circuit currents in substations, a lot of different test cases are given in Volume 2 of [Ref 1] and in Volume 2 of this brochure. In these cases, the test arrangements are described in detail, oscillograms and values of forces and stresses in the conductors and substructures, and the conductor displacements are given. In IEC Publication 60865-1 [Ref 1] and the European Standard EN 60865-1 [Ref 2] simplified methods are given for the calculation of the short-circuit stresses, forces and strength of substations with rigid and flexible busbars. The physical background and the derivation of these methods are outlined in the sections 3 and 4 of [Ref 1] and section 3 of this brochure. In the following, the data of the tests with flexible conductors are taken and a calculation according to the standard is carried out. The comparison of the calculation results with the test results is shown in diagrams and is discussed. For the design of busbars, the maximum short-circuit duration Tk is stated by the protection concept. The actual short-circuit duration tk is unknown, it can be lower and can lead to higher tensile forces than with Tk. Therefore the maximum values are determined using the standard [Ref 2, Ref 3] which occur within 0 < tk ≤ Tk [Ref 1]. In contrast, the short-circuit duration tk is known when calculating tests and out from this the swing-out angle δk at the end of the current flow, see Equation. (4.8) in [Ref 1]. If tk ≥ Tres, the conductor swings out to its highest position at δm = 2δ1 and then back. Tres is the resulting oscillation period of the span during current flow and δ1 = Arctan r the direction of the maximum radial force Ft. r means the ratio of electromagnetic force and gravitational force on the conductor. If tk ≤ Tres, δm = Arccos(1 – r sin δk) holds; Ft is maximum at δ1 if δk ≥ δ1, otherwise at δk. Ff acts at the end of the drop down from δm. For further details see [Ref 1]. 119 When calculating the short-circuit effects of spans with strained conductors, the masses and the influence of the droppers at the ends or near the ends of the spans is neglected, see paragraph 3.3. With droppers in midspan, the calculation is done according to the method given in Paragraph 3.3. When calculating the static tensile force and the sag, the masses of the droppers have to be considered. The calculation of the pinch force Fpi is done as stated in the standard. In all cases, the static stiffness of the sub-strutures measured during the tests are taken into account. In the following diagrams, the measured values of shortcircuit forces and horizontal displacements are given on the horizontal axis (index m) and the calculated ones on the vertical axis (index c). In most cases, the forces are related to the initial static tensile forces. Each sign point represents a result, the number of evaluated tests is given in the legends. The lines are drawn marked by 0 %, +25 % and -25 %, which show the deviation between test and calculation; the signs above the 0 % line, the calculation results in higher values than the test, the signs below the 0 % line, the calculation results in lower values than the test. This presentation of the comparisons is done in three parts: − Slack conductors on supporting insulators, − Strained conductors fastened with insulator strings on towers, − Tests only for bundle pinch effect. In the following, the numbers of test cases presented in Volume 2 of [Ref 1] are marked by *, the numbers of test cases presented in Volume 2 of this brochure are not marked. For the details of the tests, reference is made to both volumes. 8.3.1. Slack conductors on supporting insulators Case 1 (FGH 1972) In this case, a 110-kV-structure is tested. The stress in the bottom of one insulator is measured and hence an equivalent static force on the top of the insulator is calculated, which gives the same stress in the insulator as the short-circuit force. If the subconductors fulfil either a s/d s ≤ 2,0 and l s/a s ≤ 50 or a s/d s ≤ 2,5 and l s/a s ≤ 70 (so called close bundling), the conductors are considered to clash effectively; then the pinch force F pi does not have to be calculated, the short-circuit tensile force F t is to be taken, Figure 8.10a. On the other hand, if the conditions are not fulfilled, the maximum of F t and F pi is decisive, Figure 8.10b. A good agreement is achieved. Cases 2 and 3 (FGH 1978)
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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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for the maximum outswing and the ma
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Zug-/Druck-Kraft in kN Z eit in s F
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Page 98 and 99: power converter in a three phase br
Page 100 and 101: The time functions of the currents
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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
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Page 114 and 115: Figure 8.2 What is ESL in this case
Page 116 and 117: As the eigenfrequency of the portal
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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The mechanical effects of short-circuit currents in - Montefiore

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