Lowering Voltage to Elevator Drive

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infinity

infinity

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Had an interesting day at work today. Seems that our 4000 amp, 208Y/120 volt temporary service has a POCO voltage that's a little high. We're using a 208-480Y/277 transformer (which has no taps) to get the 480 volts that the elevators require. At the elevator controller we have 511 volts, which occasionally faults the drive for over-voltage. It was decided (not by us) to add a 3Ø, 100kw load bank at the controller location to create a voltage drop so the elevators would see around 480 volts. Anyone care to guess how that went?
 
J

JFletcher

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without appropriate HVAC equipment to remove all that extra heat, I'm guessing something caught on fire?

Eta: was your solution to have a 208 / 480 Transformer with taps?
 
infinity

infinity

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The unit was in the elevator machine room which heated up rather quickly when we turned it up to the full 100,000 watts. I'm guessing that pumping 511 volts into it had something to do with it overheating and exploding. A transformer was what we had suggested but someone liked the load bank better.
 
Jraef

Jraef

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Sorry, but that's just... I dunno the right word... maybe, NUTS? :blink:

A couple of bell transformers configured as bucking autotransformers would likely have cost them less.
 
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Ingenieur

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the plan was to lower v by creating v drop by adding load?
basically in parallel with the drive?
and put it in the machine room
does the drive regen?
that likely violates A17.1

was the 511 under load or quiescent?

get some 3% filter chokes
 
Z

zbang

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infinity said:
It was decided (not by us) to add a 3Ø, 100kw load bank at the controller location to create a voltage drop so the elevators would see around 480 volts.
Click to expand...

As the college prof would say "That's an interesting approach to the problem."

I don't suppose the person involved was a movie set electrician? I've seen some of them do some pretty dodgy things (like using 100' of 14g as a "dimmer" for IIRC a 5kw load; if you keep the duty cycle down, it does work for a while).
 
infinity

infinity

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I don't know exactly who came up with the load bank idea but well it didn't work too well. Even with the thing running at full blast the voltage only dropped to about 502 volts.
 
J

JFletcher

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Jraef said:
Sorry, but that's just... I dunno the right word... maybe, NUTS? :blink:
Click to expand...

You know the right words, and none of us can print them on this forum.

I'm sorry, but that idea is so monumentally stupid that whoever thought of it should probably die of embarrassment, I won't go so far as to say anything about the electrician's that hooked it up other than those guys must really love their jobs or wanted an early 4th of July.

Where did they think they were going to dissipate a hundred kilowatts of heating load to? And even if this was a temporary set-up, the power cost of running a hundred kilowatt load Bank 24/7 would very quickly exceed the cost of the proper transformer.

If this was an April Fool's story, I would not have believed a word of it. It's just so far beyond the realm of comprehension that's something like this should never ever happen. I bet the proper transformer is a heck of a lot cheaper than a whole new elevator room.

So, how many people are getting fired over this? I hope nobody got hurt.
 
infinity

infinity

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This is another example of some of the stupidity we have to deal with out in the field everyday. :roll:
 
steve66

steve66

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I can't imagine paying the power bill for a 100KW loadbank just to drop the voltage.

Wouldn't just replacing the xformer with one with taps be a lot cheaper, even from a first cost standpoint?

Nuts, just nuts.

It would be somewhat embarrassing (to whoever suggested the load bank) if the drive has an adjustment for the setpoint of the overvoltage fault (or even a way to shut that feature off).
 
infinity

infinity

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I was testing the voltage at the controller on the other side of the room when someone walked over to check the load bank and saw this. The photo was snapped just before the thing blew with a nice fireball emerging from the vented section.

IMG-20180530-WA0005.jpg
 
augie47

augie47

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Follow the $$$ :) see how much stock in the power company is in the hands of the guy who made the suggestion :D
 
infinity

infinity

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petersonra said:
those kind of load banks are notorious for over heating. they are really not made to be run continuously.
Click to expand...

I wouldn't doubt that the combination of the applied over-voltage and the thing being faulty had something to do with it. I would guess that it's possible that the hot spot at the bottom of the photo could have been caused by a failed cooling fan. The unit ran for barely five minutes.
 
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