Name: Peter M.
I am working for
Bombardier Transport with electric trains. On AC driven trains (25 kV 50
Hz) we have problems to explain why a DC current is produced in the primary
of the main transformer when we run with in cold weather with ice on supply
line thus creating continuos arcing in the contact surface between the
overhead line (copper) and the current collector (carbon) on the train. One
theory is that some diode rectification or DC emk is created in the surface
between copper supply line and carbon current collector when an arc is
The question is: What does actually happen in a surface between
copper and carbon when an arc is conducting an AC current?
I would suggest the possibility of an inadvertent arc
e.g. analogous to a mercury arc rectifier of old.
Such rectifiers, when designed, are sealed, and quite efficient.
One might get a similar result, inadvertently, in the situation
Dave P. via Bill Robinson
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Update: June 2012