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Dear Sir,

Can anybody give the relation (Mathematical formula) of DC current and AC current in a three thyristor speed controller of DC motor?

Thanks in advance.

Responding to James Isaac's 20-Nov-07 (19:54) question... there are number of relationships depending on the configuration of the thyristors.

If you are interested in just converter-input to convert-output, voltage and current ratios (without intervening transformers, then typically, their full-load ranges are 0.741 - 1.11, and 0.577 - 0.707, respectively. Of course, if you are interested in more detail, then I suggest any text covering A/C power converter electronics.

Regards, Phil Corso (cepsicon@aol.com)

Dear Mr. Phil,
I am looking for the relation of AC and DC current for the Three Phase Thyristor bridge fully controlled convertor used for Speed control of DC Motor. My DC motor max. Current is 1800 Amphere. I need to select a suitable AC breaker in the incoming. What is the relation of currents (AC and DC)? I use a DC choke at the convertor output.

Regards

James, for a 3-ph thyristor-bridge converter, the AC-line current is [sqrt(2/3)]xId (or 0.8165), where Id represents the DC-motor's maximum current.

Caveat: The smoothing-reactor's reactance, Lr, should be at least one-order of magnitude greater than the equivalent line-reactance of the AC supply source!

Regards, Phil Corso (cepsicion@aol.com)