Contact Physics – Formulas

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/32N² x \sum \sum (s_ij) i \neq j (Multi-spot contact according to Greenwood considering the influence between the spots)

• Contact resistance
  R_K = R_e + R_f

• Path resistance
  R_d = R_b + R_K

• Contact resistance and contact force
  R_K = 280D ³ E(F · r) K

(According to Holm model for film-free spherical contact surfaces with plastic deformation of the contact material; F_k < 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; F_k > 5 N for typical contact materials)

• Dynamic contact separation (without considering magnetic fields caused by the current path)
  F_A 0,8 x I²(Rule of thumb with F_A in N and I in kA)

• Contact voltage and max. contact temperature
  T_kmax 3200 U_K

• Contact resistance at higher contact forces (according to Babikow)
  R_K = cF -m K

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

References

References