From: ghost.crapper@gmail.com   
      
   On Friday, April 2, 2021 at 10:16:12 AM UTC-6, Big Bad Bob wrote:   
   > On 2021-03-16 22:13, Trevor Wilson wrote:   
   > > Each week, the Diesels would be fired up for 30 minutes or so for   
   > > testing. There was a big meter mounted between the Diesels. Apparently,   
   > > the needle had to be centred, when the Diesels had reached an in-phase   
   > > operation. Then they could be switched in. I asked what would happen if   
   > > they were switched when not in phase. Apparently all the trainees asked   
   > > that question. No one knew for sure and they didn't want to find out.   
   > > Probably a lot of structurual damage would occur.   
   > Well it's kinda like this...   
   >   
   > When I was in the Navy I was qualified to run the nuclear reactor on a   
   > sub. This included being qualified to run the electric plant as well   
   > (turbine generators, motor/generator sets, and a diesel generator mostly   
   > for emergencies). The phase meter you refer to is used to parallel two   
   > 3-phase generators. The Navy used a manual control system that was   
   > relatively foolproof, somewhat universally throughout the fleet.   
   > Submarines were pretty much the same that way.   
   >   
   > If you plot the sine wave patterns for the generator output vs power   
   > already on the bus (let's say with an o-scope), in order to minimize the   
   > inevitable current spike you get when shutting the generator's breaker,   
   > the output and the line have to be in phase and at the same AC voltage.   
   > Ideally it's a zero volt difference, but in practice the best way to do   
   > it is as follows:   
   >   
   > a) speed regulator on the engine has a "load curve" so that increasing   
   > its setting may keep the same frequency, but takes up more load from the   
   > other generators and utility power.   
   >   
   > b) The incoming generator is moving slightly faster. As the phase   
   > needle spins clockwise, you time shutting the breaker [which has a delay   
   > - you get used to how long that is] so that it physically shuts the   
   > moment the needle is at the top [in phase].   
   >   
   > c) once the breaker shuts you immediately put load on the generator by   
   > increasing its speed regulator setting. You don't want a turbine   
   > "windmilling" nor an engine being driven by incoming power for any   
   > length of time. [some generators might have reverse-power trips on   
   > their breakers to prevent this]   
   >   
   > d) when you 'secure' the generator, you decrease the speed regulator   
   > setting until all the load is off, then pop open the breaker just as it   
   > hits zero.   
   >   
   > Hopefully that explains how those phase meters work and why they are there.   
   >   
   > Now, for the question "what could happen if you do it wrong"... well, in   
   > the worst case scenario (180 degrees out of phase)   
   >   
   > a) melt the contacts on the breaker, hopefuly not causing a phase-phase   
   > short in the process   
   > b) start a major electrical fire (buswork or generator itself)   
   > c) physically torque the generator and damage the shaft and/or windings   
   > d) snap the crankshaft on the diesel generator   
   > e) torque the engine/generator so hard they either separate from one   
   > another, or jump off of their mounts and damage things while rolling   
   > around the room   
   >   
   >   
   > Yes. You do NOT want to parallel them out of phase. EVAR. It is worse   
   > than suddenly putting a shorting bar across all 3 phases simultaneously.   
   >   
   >   
   > --   
   > (aka 'Bombastic Bob' in case you wondered)   
   >   
   > 'Feeling with my fingers, and thinking with my brain' - me   
   >   
   > 'your story is so touching, but it sounds just like a lie'   
   > "Straighten up and fly right"   
      
   SO - you was a squid, huh?  Me too - avionics technician. My class   
   was the last one that was taught entirely on tubes - after us, the   
   training manuals and films and whatnot were all updated and the   
   boots all had to learn about them three-legged fuses along with   
   the tubes.  That was in 1968. Those old training rigs were really   
   a hoot - every single component in the unit was mounted on a   
   small turret board with a thumb-wheel hold-down fastener on   
   each end. The instructors had a big box of BAD components   
   which were outfitted the same way; before class, they'd go through   
   and randomly install bad parts in the trainer chasses - that way,   
   when you powered 'em up, they all had different stuff wrong with   
   'em, to which you applied your recently-acquired troubleshooting   
   skills in order to find the fault. Sometimes, you found it.  ;-)  I wonder   
   what happened to all those old training rigs...   
      
   Lord Valve / Fat Willie   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)