Sounds like this might have been a synchronous condenser drawing lagging load from the grid to lower the voltage provided by the utility.

xnuke
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Open neutral?

Quote:

Sounds like this might have been a synchronous condenser drawing lagging load from the grid to lower the voltage provided by the utility.

That gets real expensive, real fast.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

Synch condenser provides a "harmonic dump" for all the other electronics and nonlinear loads (including lighting ballasts) in the building. As soon as it's turned off, all those electronics get hammered by the "dirty" bus and voila - instant crispy. Seen this happen a few times - but usually on a MUCH larger scale, and/or on an effectively-islanded system (marine shipboard or offshore platform).

Converting energy to motion for more than half a century

On islanded generation, that may be load dump. The voltage regulator can not react in time to losing a large load and the voltage spikes.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

Maybe it was a rotary phase converter?

Send the bill to the building inspector's department, demanding payment for engineering negligence.

Were all of the branch circuits that fried single phase, low voltage loads? Is the synchronous connector in a wye configuration? Is the center point of the wye grounded (it should not be)? If these cases are true I would lean towards waross's suggestion of an open neutral.

If you were to have 3 conditions of a grounded center tap in the synchronous motor, a ground fault on any line, and an open neutral then opening the contactor for the synchronous condenser would cause your 2/3 of your low voltage circuits to rise to line voltage. The ground fault will not clear itself due to the open neutral.

I initially thought RPC too. So by disconnecting it, all of the 3 phase equipment was instantly single phased and anything running was fried, then that caused collateral damage to other things.

The synchronous condenser is a good idea too, but generally those are for really large facilities with lots of induction motor loads. "Educational/assembly building" doesn't sound like a place that would have the need of a synchronous condenser.

" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

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really large facilities with lots of induction motor loads.

Years ago I worked on construction of a large mine mill.
There were six autogenous ore mills, each driven by a pair of 3000 HP wound rotor motors.
The mills needed the breakaway torque of wound rotor motors to start turning under 100 tons of ore.
Also, synchronous motors are challenging to load share when run mechanically coupled together.
One method of load sharing that I have read about was a micrometer adjustable coupling.
Possible but not easy at 3000 HP.
With paired synchronous motors, one motor is run and the phase angle other motor's generated potential is checked.
The phase angles are adjusted as close as possible by changing the tooth matching on a common ring gear and the final adjustment made with the micrometer coupling.
As well as the 36000 HP of main motors there were a couple of acres of flotation cells with 5 to 10 HP motors.
There was a fairly large building just to house the synchronous condensers.
The liquid rheostats for starting those motors were interesting as well.
Three rheostats, two working and one spare.
Then a large assortment of contactors.
Any two rheostats could be used to start any pair of motors.
As jraef said; Synchronous condensers are for really large systems, and then as a second choice after oversized synchronous motors.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

Would a star connected synchronous motor on a 3-phase system be useful for balancing voltages on a system with poorly balanced single phase loads?

If no-one knows WFT the thing is exactly, there is NO possible way it was a synchronous motor and has just "been working" for 10 years. I'm doubtful a rotary phase converter could have just "been working" for 10 years either.

Some good pictures would help, otherwise who knows and everything is just guesses.

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Would a star connected synchronous motor on a 3-phase system be useful for balancing voltages on a system with poorly balanced single phase loads?

Hang a star/delta transformer bank on the system.
The delta must close on itself. Any imbalance on the primary (eg; Unbalanced system) will cause a circulating current in the delta which will work to equalize the primary voltages.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

Or just balance the loads....