Friday, May 01, 2009

Good Morning

My day dawned bright and early - well, at least early -- after two days of mounting frustration (indeed, at times it seemed as though frustration was mounting me and not in a good way).

Yesterday afternoon, three days of work on one of the Stardrive power amplifiers finally resulted in what so far appears to be success, when I installed the last "floating" power supply we had aboard ship. What it "floats" on is the 36,000 Volt power supply rail, to which all the lesser phantsmajector voltages are referenced: 3 kV for the ion pump, a few hundred Volts to bias the grid and a mere five to seven volts (at some hundred Amperes!) just to light the tube up. It passed all the preliminary tests, so we slapped both high voltage and RF drive to it and whattaya know, there was both output and a distinct lack of overload conditions, a condition that persisted through the end of my shift.

Called Drive Control this morn, still a little asleep, and the DQ op on duty responded with a smile in his voice, "All three finals are clean and green!"

First time I've heard that news in a good long while. Let's hope it lasts us 'til the upcoming refit -- word is there's something Way Better TM in the works!


sam said...

36,000 volts? That's a heck of a "third rail," m'dear.

I'm not an EE, so just how do you deliver high amperage at 3 volts?

Roberta X said...

High current at low voltage? No EE required: you use big, fat wires. At DC and low frequencies, cross-sectional area is the key. At higher frequencies, there's a thing called "skin effect," and the surface area becomes the limitation on ampacity; flat copper strap or even hollow conductors like copper water pipe are the answer, with various sneaky workarounds.

37kV is ... a bit hot. No exposed metal connected to it has less than 1/4" radius in any single plane, and wider than that if is is closer than 4" to any surface at or near ground potential.

The power supply weighs about 7,000 pounds (that's American, Brits will have to convert to dollars and back to Pounds Sterling or better, Guineas, then to stone and finally either to kilograms or degrees C, depending on the time of day)and most of is it immersed in transformer oil, both for cooling (it conducts heat better than air) and insulation (it conducts electricity worse than air).