Core segments across a reactor gap attract magnetically. Assembly preload and operating magnetic pull act through spacers, tie rods and supports, but their effects depend on the mechanical arrangement. Adding their magnitudes without a free-body diagram can assign the wrong load to a component. [1]
Draw one segment and every force acting on it. Include spacer compression, tie-rod tension, support reaction and magnetic attraction. Identify which contacts are unilateral: they can carry compression but cannot carry tension when separated.
Record loads by path and state
| Element | Initial state | Operating question |
|---|---|---|
| Gap spacer | Compression from assembly | Maximum pressure and possible loss of contact |
| Tie rod | Pre-tension | How geometry redistributes tension during pull |
| Segment support | Static support reaction | Cyclic load and permitted movement |
| Interface | Contact area and friction assumption | Opening, slip or local pressure concentration |
Separate mean and cyclic magnetic force
For an ideal normal field in a nonmagnetic gap, p = B²/(2μ₀). A sinusoidal 50 Hz field gives a mean pull plus a 100 Hz component. Integrate the actual face field; fringing and tilt can concentrate pressure. [1]
For the specified closed linear rod/member joint, let C = krod/(krod + kspacer). An inward closing load P reduces rod tension by CP and increases spacer compression by (1−C)P until the assumed contact model changes. [2]
Compare magnetic pull with the preload path
Assumptions: B = 1.0 sin(2π50t) T is uniform and normal over 0.010 m²; μ₀ ≈ 4π×10⁻⁷ H/m. Peak pull is 3.979 kN. A closed linear joint starts with 3.0 kN rod tension and equal spacer compression, with stiffness fraction C = 0.25. At peak pull, rod tension is 3 − 0.25×3.979 = 2.005 kN; spacer compression is 3 + 0.75×3.979 = 5.984 kN. The spacer exceeds an assumed 5.5 kN ceiling by 0.484 kN. Hold that spacer/load-path assignment; the magnetic force is not subtracted from every preload. [1] [2]
References
- H. B. Duc, T. P. Minh, T. P. Anh and V. D. Quoc, A Novel Approach for the Modeling of Electromagnetic Forces in Air-Gap Shunt Reactors, Engineering, Technology & Applied Science Research 12, 8223–8227, 2022. DOI: 10.48084/etasr.4692.
- R. T. Barrett, Fastener Design Manual, NASA Reference Publication 1228, 1990.