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Name: Peter M.
Status: Other
Age: 30s
Location: N/A
Country: N/A
Date: 2002


Question:
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 present.

The question is: What does actually happen in a surface between copper and carbon when an arc is conducting an AC current?



Replies:
I would suggest the possibility of an inadvertent arc rectifier, 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 mentioned....

best

Dave P. via Bill Robinson



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