The mechanical effects of short-circuit currents in - Montefiore

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As the eigenfrequency of the portal is around 4 Hz, ESL factor synthetic curve given in chapter 3 is 1.4 So that the portal design loads obtained by simplified method recommended in this brochure is : Load on phase 1 : max (Ft, Fst) x 1.4 = … Load on phase 2 : idem (only two phase for this test) and these load can be considered as static load. 8.2. CLAMPED-FREE BEAM DYNAMIC RESPONSE TO A TOP LOAD IDENTICAL TO A SHORT-CIRCUIT FORCE. ESL VALUE, ESL FACTOR FOR DIFFERENT STRUCTURAL DATA OF THE SUPPORT. This case is different from the former one, as the load application has not the same shape as the load applied to flexible busbars. This case is more close to rigid busbars for which we would like to know how to design supporting structure (insulator support). We would like first to emphasise that no synthetic ESL factor curve had been given for this case in this brochure. This case is reserved here just to point out what could be ESL load and ESL factor in a simple case. 8.2.1. The geometry Figure 8.6. A clamped-free beam with uniform mass distribution. Internal damping chosen as 2% of critical on the first eigenmode. 8.2.2. Excitation Top load time definition ⎛ ⎜ ⎝ using τ = 60 ms φ = −π/2 ν = 50 Hz A = 1000 N (8.2) F () t = A⎜sin( 2πυt + φ ) − sin( φ ) e t − τ ⎞ ⎟ ⎠ 2 116 Observation time of the time response is fixed to about 0.4 s in all cases. We have treated three different case, only by changing the structural data to change its frequencies. These values are taken from typical supporting insulator data's used in substation from 110 kV to 400 kV. At least one of the three first eigenfrequencies is tuned to be resonant with either 50 Hz or 100 Hz. That is to show the dynamic effects in such structure. As the structure is supposed to be uniform mass distribution, if one frequency is fixed, the other are easily evaluated by classical beam theory. 8.2.3. Examples a) Case study number one The 50 Hz is the first eigenfrequency, thus 300 Hz is the second and 850 Hz is the third. Which has been reproduced using following data : ( a typical 110 kV insulator support) : height of the support 0,77 m bending stiffness of the support : 5,9e5 N/m Figure 8.7 Case 1 (first eigenfrequency of 50 Hz). Curve a) is the top displacement of the insulator (m) b) is the applied top load in N and c) is the bottom bending moment (N.m).
- There is a 50 Hz oscillation of the beam during the 50 Hz dominant load application. The Resonance is clearly enhanced. - The maximum displacement at the top is around 180 mm at around 0,9 s. - Bending moment is in phase with the top displacement. ESL factor can easily be determined : Max bending moment around 9000 N.m means ESL = 9000/0.77 = 11700 N. Max dynamic load value (not at the same time as the max bending) : around 3500 N. ESL factor = 3.3 b) case number 2 The second eigenfrequency is at 100 Hz, which give a first one at 16 Hz . Which has been reproduced using following data : ( a typical 245 kV insulator support) : height of the support 2.3 m, bending stiffness of the support : 1.8e5 N/m. - There is a 16 Hz oscillation of the beam during all the time with very low damping. - The maximum displacement at the top is around 120 mm at around 0,02 s. - Bending moment is in phase with the top displacement but has a clear presence of 100 Hz component. ESL factor can easily been determined : Max bending moment around 6500 N.m (means ESL = 6500/2.3 = 2800 N) Max dynamic load value (not at the same time as the max bending) : around 3500 N ESL factor = 0.8 117 Time/s Time/s Time/s Figure 8.8 Case 2 (second eigenfrequency of 100 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. c) case number 3 The third eigenfrequency is at 50 Hz, which give a first one at 4 Hz . Which has been reproduced using following data : ( a typical 400 kV insulator support) : height of the support 3.8 m bending stiffness of the support : 0.9e5 N/m
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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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Page 100 and 101: The time functions of the currents
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Page 106 and 107: 7. REFERENCES Ref 1. IEC TC 73/CIGR
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Page 110 and 111: Ref 80. Fiabilité des structures d
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