On Wednesday 13 February 2013 22:44:21 Przemek Klosowski did opine: > On Wed, Feb 13, 2013 at 9:59 AM, Stephen Dubovsky <smdubov...@gmail.com> wrote: > > Disconnecting a motor from drive/vfd isn't the problem. Reconnecting > > it while its still powered is what typ lets the magic smoke out. > > Gene had a good point, that a mechanical contact never goes > monotonically from 'connected' to 'open' due to contact bounce, so you > end up disconnecting and reconnecting over and over--but I can see > that different output stages will be affected to a different degree. > > Today I learned how a HVDC breaker work: it's clever and maybe > relevant because that's the kind of trouble one has to go through in > power applications: > > ----lowSpeedContact-----+----highSpeedContact---lowVoltageSolidState---+ > ------- > > |___highVoltageSolidState__________________| > > it starts by having all switches closed; the hVSS switch has high > resistance so most of the current goes through the hSC and lVSS. > First, they open lVSS, which causes the current to go through hVSS, > which starts to heat up like crazy, so they quickly open hSC (it has > no current flowing so it won't arc). Then they open hVSS before it > melts down, and finally open lSC to cut off the leakage current. We had to develop something like that but much simpler because we had a few tens of milliseconds to get the job done and save a pair of $150,000 klystrons.
The original failure during the autopsy was the failure of one contact in a 3 phase 40 amp Heineman breaker, which was supplying the water pump that was circulating about 90 gallons a minute thru the collector buckets of a pair of high power klystrons for cooling, a rather important detail when the input is a few volts shy of 20,000 volts at a current in the visual tube of about 5.8 amps. Nominally 115 kw worth of heat in a collector bucket that may have had 1.5 gallons of water/glycol in it at any one instant. I was in the building, heard the 15 hp pump motor do a growp to a solid shake the building hum as it stopped from being single phased, and my hand made it about 18" of the 3 feet to the kill button when the main entrance breaker went down like a 4 gage punt gun and everything was dark and silent, followed by the standby starting, a 150 kw powered by a 335hp Cummalong. The Visual klystron was full of coolant where there should have been a very good vacuum. The electron beam cut a hole thru the copper funnel that catches it, taking perhaps 1/2 second to pierce it & let the coolant in. And KXNE-TV was off the air until a quorum of the legislature could be called in to authorize the purchase and allocate the money for a new klystron. But to prevent a recurrence of that scenario at any of the other state owned tv stations, all were retrofitted with a phase detection circuit that sealed in a 50 kilovolt, 50 amp rated Jennings vacuum relay, so the next time we got single phased for any reason, the high voltage was removed from those klystrons in about 30 milliseconds. The GE AK2-25 breaker was instructed to open at the same time, but it was a cycle or 2 slower, so the 20 kilovolt rated filter caps in that 3 phase supply shot up to around 35 kilovolts, but they held without any explosions which would still have been cheaper than one of those 2 klystrons were. We even tested it by, while old klystrons were in it yet, walking over and throwing the new replacement breaker off several times. Then I installed the new one and got back up to full power. Not as complex as your description of course but then how would you apply that to a 175 kw 20 kilovolt supply? Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> is up! My views <http://www.armchairpatriot.com/What%20Has%20America%20Become.shtml> modem, adj.: Up-to-date, new-fangled, as in "Thoroughly Modem Millie." An unfortunate byproduct of kerning. [That's sic!] I was taught to respect my elders, but its getting harder and harder to find any... ------------------------------------------------------------------------------ Free Next-Gen Firewall Hardware Offer Buy your Sophos next-gen firewall before the end March 2013 and get the hardware for free! Learn more. http://p.sf.net/sfu/sophos-d2d-feb _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
