Contact Physics – Formulas

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6.4.2 Contact Physics – Formulas

  • Constriction resistance R_e = \rho/2a

(Single spot contact according to Holm; circular touching spot between clean contact surfaces) R_e = \rho/2Na (Multi-spot contact according to Holm without influence between the N individual spots) R_e = \rho/2 x \sum a_i + 3 \pi \rho /32N^2 x \sum \sum (s_ij) i \neq j (Multi-spot contact according to Greenwood considering the influence between the spots)

  • Contact resistance RK = Re + Rf
  • Path resistance cRd = Rb + RK
  • Contact resistance and contact force R_K = 280\rho \sqrt[3]{E (F_K \cdot r)}

(According to Holm model for film-free spherical contact surfaces with plastic deformation of the contact material; Fk < 1 N for typical contact materials) R_K = 9000 D H/ FK (According to Holm model for film-free spherical contact surfaces with plastic deformation of the contact material; Fk > 5 N for typical contact materials)

  • Dynamic contact separation (without considering magnetic fields caused by the current path)
    FA 0,8 x I2(Rule of thumb with FA in N and I in kA)
  • Contact voltage and max. contact temperature
    Tkmax 3200 UK
  • Contact resistance at higher contact forces (according to Babikow)
    RK = cF -m K

For FK between 10 and 200 N c = material dependent proportionality factor m = shape dependent exponent of the contact force

References

References