Sudden reversal in a simple 3-phase motor's direction

  • #26
10
12
Yikes! You're lucky nobody was hurt. The whole thing could have melted and flown apart. There are sync check relays to prevent mistakes, but those relays too can be wired incorrectly.
Thank you for your concern. I had a sync check relay as part of the synchroscope in circuit at the time, but as it only looks a single phase on each of the grid and generator, there is no way for it to check phase rotation. That part is the responsibility of the commissioning engineer (me) and I'd already done that the previous day and run tests, but then someone, unkown to me, had swapped an extension cable with one that had the phases crossed over!

I am not quite sure how the whole thing could have melted in the 20 ms or so that the breaker took to trip, but the inertia could have done some damage. As I said, luckily it was a small system which has significant resistance and reactance in both machines. It is that which prevented a more serious incident. Incorrect phasing / synchronisation of larger machines has resulted in the generator ripping free of it's mountings and bending it's shaft through 90 degrees. I guess it also flung itself a fair distance too, but thankfully I have never been present!
 
  • #27
10
12
Wow 7.5kw sync'd out of sequence ? Lucky it didn't throw itself at you !
Yep! The torque reaction was such that it's top rotated away from me. I guess it pivoted between the lower back edge of it's chassis and the bench. As always, when carrying out tests like this I stand well away from the machine and to one side so as not to be in line with anything it might spit out! I kinda like living! ;)
 
  • #28
jim hardy
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The brass ball float turned up in a load of old plumbing scrap a couple of weeks ago. At the time I did not know why I needed to rescue it, maybe there is something in heart-strings-theory after all.
Too much to do in the time before the instant of the winter solstice here, Jun 21, 10:07 UTC.
ToiletfloatMotor2.jpg


You have three phase ? I'm green with envy.

I make small amounts with a stereo audio amplifier.
Make 60 hz from a doorbell transformer and volume control.
One channel gets that sinewave, call it A
Other channel gets that sinewave after shifting 60 degrees and inverting, call it C.
Now you have open delta three phase with B at circuit common.

Best of luck with your experiment !

old jim
 

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