Re: [CAD_CAM_EDM_DRO] Re: Mariss' power supply circuit

At 03:14 AM 6/20/02 +0000, you wrote:

>> Shorting the armature of a motor while it is spinning at high
>> speed will also cause 50-100 times rated current to flow.

I'd like to see the math on that.

>> with a short, there is no current limit.

Sure there is; the windings themselves have resistance.

>> of one case where the semiconductors in a DC drive failed,
>> shorting the armature of a 25 HP motor while it was spinning
>> a roller on a paper machine (high inertia load). The fault
>> current generated enough braking torque to snap the shaft of
>> the motor (around 2" in diameter)!

I hate to sound doubtful but I am. The impulse generated when shorted to a
stop is no bigger than the impulse when shorted to start, IE, no bigger
than the impulse generated the instant you put it under power from rest.

>Due to poor installation of bus bars in a large coal-fired generating
>station near here (Labadie plant near at Labadie, MO) two
>sets of bus bars carrying the output of two 840 MVA alternator sets
>at 14 KV flew off their insulators and shorted the two alternators
>out. The alternators were ripped partly out of the floor

This is a bit more believeable, as the tie-down bolts for these big
alternators aren't really huge. But it didn't break the drive shafts, did it?

>The rotors of these alternators are HUGE, of course, a solid billet
>of steel about 18" diameter and 6 to 10 feet long!

No lams? Darned odd that.

Regards, Hoyt


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