VFD Restaurant hood MUA unit question

D

David Allison

Member
Location
Raleigh, NC
Occupation
Electrician
I'm connecting a new exhaust hood and Make Up Air unit for a restaurant. Hood manufacturer supplied VFD's for both. The MUA unit vfd will need to be located remotely, there is no room in housing to mount it. Now I will have a disconnect for the remote vfd and a factory installed disconnect for the motor on the roof. I need to find out if the VFD will get angry and break if someone disconnects the unit on the roof for service WITHOUT ALSO disconnecting the vfd. The VFD is a Lenze i510 protec. Some of the warnings make me think a disconnect on the manufactured phases are bad for the vfd. And if this is the case, what kind of control circuit/relay/shunt breaker would you recommend for the rooftop disconnect to also kill the upstream VFD disconnect.
 
Depending on the drive - some will shut down output if you open the output circuit others will not.

In all cases you don't want to close the motor into active drive output, you want the drive to completely control motor acceleration.

Closing motor into active output has much greater risk of damaging the drive than opening circuit of an active output.

Aux switch in disconnect to shut down drive input control circuit is still good idea even if it isn't one that opens before the power circuit.
 
kwired said:
Depending on the drive - some will shut down output if you open the output circuit others will not.

In all cases you don't want to close the motor into active drive output, you want the drive to completely control motor acceleration.

Closing motor into active output has much greater risk of damaging the drive than opening circuit of an active output.

Aux switch in disconnect to shut down drive input control circuit is still good idea even if it isn't one that opens before the power circuit.
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On the safety switches that I took readings from ( voltage drop & IR scan with FLIR camera ) they had a micro switch that contactors were closed when the safety switch was turned off. The micro switch is supposed to open before safety switch blades. In that case you would have to go back to the drive or control room to restart the drive. For some reason an entire $800 millon dollar 12 story building built ten years ago and well over a hundred drives did not have any micro switches on the safety switch on load side of drives. They spent extra money where every drive 40 HP & larger we're 18 pulse drives. Anyway the contractor performing maintenance on three 75 HP tower fans did not want to climb down maybe 75 steps to third lowest basement boiler room to use selector switch on drives so he turned safety switches on & off by using roof top safety switches. Two drives went down. One might have only needed two fuses replaced but the other had to have a board replaced. We had some drives where you could not defeat the door switch to open a drive while running and had four drives with cast aluminium covers and exposed 480 volt buss bars close to cover. Would turn HOA selector switch to off, turn disconnect off open cover then turn disconnect switch on & restart drive where the VFD performing a flying start on rotating fans. Never caused any problems. Fans usually had a least 5 minute ramp up time. V belts lasted a lot longer with long ramp up time.
 
YASKAWA dealer here:

Generally, it's always bad to "cut the nuts off" of a drive with a disconnect, under load. Best practice is to stop the drive, wait until there is no load, then disconnect power. NEVER use a disconnect on the output of a drive. You will kill the bus if you shut it off like that.
 
herding_cats said:
YASKAWA dealer here:

Generally, it's always bad to "cut the nuts off" of a drive with a disconnect, under load. Best practice is to stop the drive, wait until there is no load, then disconnect power. NEVER use a disconnect on the output of a drive. You will kill the bus if you shut it off like that.
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The one 12 story research building was extremely difficult to shut some drives down. One floor grow something for patients that took ten weeks. If they lost HVAC or power for more then a few seconds they had to contact a government office and start over costing tens of thousands of dollars. Even though the building had dual 13.2 KV services & three 2,000KW gen sets they installed a separate 13,2KV generator thru more ATS'S and even Manuel 480 volt panel bypasses with Kirk keys for upmost power backup. My thinking money would have been better spent having a large battery backup UPS then adding a fourth gen set. Took six months of tooth pulling to schedule the required tri annual testing & cleaning of substations, ATS'S & rack out breakers.
 
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