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Jim Mora wrote:
Hello Tesla Friends,
Regardless of the outcome with my Raytheon Power Supply, I have completed
the Six Pulse, Full Wave three phase rectifier strings. They are comprised
of (54) each UF5408 1KV with a faster switch time than the more robust
milspec 1N5408. The peak forward surge current is 150 amps at one cycle of
60Hz versus the 1N5408 300 amps. Both are speced 700 volts reverse RMS.
Since there are effectively 6 Strings of (24) on three center tapped G10
.125" x 1.5" x 24" for each polarity (over kill on voltage maybe), but it is
easy to shunt some if desired. The center taps are the H1, H2, H3
connections. And the ends will be tied together for isolated Positive and
Negative.
I am working on the "Darwin Award" this year as the transformer tipped over
and broke my Fibula in the lower left leg - A great time to be making diode
strings!
Yikes - that had to smart! Hoping you have a speedy and full recovery.
**** Here are the questions about the dequeing Diode design****
(1) can the 2X resonant voltage come slushing back to it worse case and be
seen on the cathode? Which if I had my way this would be about 22-25KV out
(10KVA input power) say 5KV H1,2,3 transformer (12.2 KV calculated +,-)
rectified for HV out of "some" 3P transformer.
In a classic line modulator (with a DC energy storage capacitor on the
supply-side of the charging reactor), the dequeing rectifier will see a
reverse voltage of no more than Vdc. This occurs when the tank cap is
fully-charged to approximately 2*Vdc.
BTW, if you do change to a single-phase HV power supply, you will need
to use a DC energy storage capacitor that's at least 10-20X the capacity
of your tank cap to supply energy between mains recharging pulses
without excessive sag.
(2) what should be the max current rating be in such a scenario.
(10KVA/12.2KV) min = .82 amps. These diodes like to idle at about 1 amp 1.5
max at room temp to distruction. I would like to make this string 3amp
capable by paralleling (2) strings. I have heard many discussions on this
topic. Is it better to parallel each diode or entire strings? I would think
each diode... I know balancing is an issue that may need some form to
address, but keep in mind I have a glut of 300 diodes on hand, remaining.
Assuming you still plan to use a 0.05 uF tank cap and wound your own 5H
charging choke with say 50 ohms of DC resistance, and ran at up to 600
BPS, then the peak, RMS, and average charging currents will be about
1.15 Amps, 0.75 Amps, and 0.68 Amps respectively and your output power
would be about 8300 watts (using lossy model). Since your rectifiers are
rated at 3 amps average current, you have plenty of headroom to increase
the power of your system while still using single rectifier strings. A
lower voltage distribution transformer or PT (1-phase) or bank of three
(3-phase) could be supported with your existing strings.
For example, suppose you increase to 0.1uF and reduced the reactor to
3H, the dequeing diode would see 2.03 A, 1.42 A, and 1.27 A for peak,
RMS, and ave currents, and would delivery about 14.1 kW of power at 600
BPS.
Paralleling diodes is not recommended. It's almost always more
cost-effective to use strings of higher-current diodes instead. If you
did want to parallel strings, entire strings should be paralleled, NOT
individual pairs of diodes. You'll still need to derate the total
current rating, OR add series balancing resistors to compensate for
forward voltage differences across strings. Immersing the strings in oil
will help to maintain strings at similar operating temperatures. See the
following applications note for more information:
I'll post some pictures on my progress blog of the diode strings: nice,
proven construction on road warrior Professional High Power "Boutique" Tube
Guitar amps which is what I have been doing for several years. Retired now
except more fun stuff, sans broken bones or HV dire shocks ;-^) I promise to
use an over abundance of caution and respect going forward!
Please do - high power equipment can squash you like a bug (in addition
to cooking you in numerous other ways)! =:^O
Jim Mora
Next up: ... post reactor, I'll call transient reverse biased diode specs to
RF ground for the envisioned coil. I have a 4" RF air choke already.
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Best wishes,
Bert
--
Bert Hickman
Stoneridge Engineering
http://www.capturedlightning.com
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