Difference between revisions of "Contact Physics – Formulas"

From Electrical Contacts
Jump to: navigation, search
Line 7: Line 7:
 
(Multi-spot contact according to Holm without influence between the N
 
(Multi-spot contact according to Holm without influence between the N
 
individual spots)
 
individual spots)
<math>R_e = \rho/2 x \sum a_i + 3 \pi \rho/32N² x \sum \sum (s_ij) i \neq j</math>
+
<math>R_e = \rho/2 x \sum a_i + 3 \pi \rho /32N^2 x \sum \sum (s_ij) i \neq j</math>
 
(Multi-spot contact according to Greenwood considering the influence between
 
(Multi-spot contact according to Greenwood considering the influence between
 
the spots)
 
the spots)
Line 15: Line 15:
 
*'''Path resistance''' cR<sub>d</sub> = R<sub>b</sub> + R<sub>K</sub>
 
*'''Path resistance''' cR<sub>d</sub> = R<sub>b</sub> + R<sub>K</sub>
  
*'''Contact resistance and contact force''' <math>R_K = 280D ³ E(F · r) K</math>  
+
*'''Contact resistance and contact force''' <math>R_K = 280D^3 E(F · r) K</math>  
 
(According to Holm model for film-free spherical contact surfaces with plastic
 
(According to Holm model for film-free spherical contact surfaces with plastic
 
deformation of the contact material; F<sub>k</sub> < 1 N for typical contact materials)
 
deformation of the contact material; F<sub>k</sub> < 1 N for typical contact materials)

Revision as of 17:25, 26 March 2014

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 = 280D^3 E(F · r) K

(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