Altivar "SCF"

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ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
I haven't been there yet. Monday
Old ATV11HU4 drive. Single phase in three out. Rated 3 HP out.
It has been working on an existing dough mixer of 1.5 HP.
The area EC tried connecting it to a larger, new to customer, mixer of 2.5 HP. It trips the 30 amp GE breaker and displays a fault of "SCF". Short Circuit to motor.

FWIU, they are using it as phase conversion, and star/stop the mixer(s) via its ATL contactors. Would the HP change be enough to change the response of the VFD to the cycling load contactor?


I guess I'm surprised it blew the breaker vs shut down the drive on the fault.


They connected it back to the smaller mixer and it still works.

Monday.
 
VFDs do not like having loads switched on and off, on the output side. During a normal ramp up the VFD controls the output to the motor so it never sees full inrush current. During a normal ramp down the VFD is able to handle/absorb the decaying backfeed from the motor.

I would not be surprised to hear your drive has failed.
 
jim dungar said:
VFDs do not like having loads switched on and off, on the output side. During a normal ramp up the VFD controls the output to the motor so it never sees full inrush current. During a normal ramp down the VFD is able to handle/absorb the decaying backfeed from the motor.

I would not be surprised to hear your drive has failed.
Click to expand...
That’s what I told the EC, but supposedly it still works on the small mixer. I’ll know Monday.
 
ptonsparky said:
That’s what I told the EC, but supposedly it still works on the small mixer. I’ll know Monday.
Click to expand...
Then the drive has not failed. Is the onput breaker sized for the full drive rating, or was it based on the smaller motor.

For sure tell them to stop the switching between the drive and the motor.
 
jim dungar said:
For sure tell them to stop the switching between the drive and the motor.
Click to expand...
100% agree.

There are super easy ways to start and stop the motor from the VFD inputs, that's what they are designed to do. Ideally, the VFD stays powered up most of the time and the motor is controlled from one (or more) DI on the drive. You almost never want to start (or stop) the motor by disconnecting the load side connections while the drive is enabled and running the motor.

When they swapped in the new (bigger) motor, did they make the appropriate changes to the VFD parameters for the new motor? Basic things like nameplate voltage, current, power, and rated speed are going to be different. And they could be different enough to trip out the VFD (which thinks it's controlling a 1.5 HP motor).
 
The inrush current of starting the motor with the contactor is making the drive ASSume that the rapid rise in current is a short circuit. Drives are not made to handle that, which is why they ALL tell you not to use a contactor on the output side. If they don't want to change, make SURE that the Drive's Run command does not engage until AFTER the contactor has already closed, You can do that simply by running the Run command signal to the VFD through a NO aux contact of the contactor.

But also, if they STOP the motor by dropping out the contactor, that can also do damage to the drive transistors, because as the contacts open and draw an arc, that causes a rapid rise in voltage that can cause the transistors to self commutate (turn themselves on) at the wrong time and fry.
 
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