Squirrel Cage Blower and VFD

[Steve Etter]

I'm preparing to run several large 10,000 CFM squirrel cage style blowers, each with its own VFD, and I am concerned about the regenerative amperage from the motor when stopping. I'm well set up already with full access to all parameters and have verified rotation, I just want to prevent problems.

Does anybody have any recommendations about how to correctly set these up - parameters to address, configuration, etc.?

Steve

 

[dmargineau]

Dynamic Braking if the provisions exist.
Regenerative type VFDs with properly configured RAMP rates if feasible.
If not, STOP by COASTING.

 

[Tom Jenkins]

If the process permits stopping by coasting is certainly a viable way to go. You can always add DC injection braking at the very end of the stop cycle.

However, the high inertia can still cause problems during normal acceleration and deceleration during speed adjustments. You will probably have to adjust the accel and decel times to prevent trips. If accel is to short you will have over-current trips, and if decel is too short you will have over-voltage trips.

I've noticed that the ability to handle high inertia loads varies significantly from VFD brand to brand. Cutler Hammer seems to handle them well, GE poorly, for example.

 

[Steve Etter]

The process is really very forgiving so coast-to-stop is not a problem. Same for accel-decel times. To start with, I am thinking 10 seconds to accel and 60 seconds to decel.

One other concern is restarting while the motor is still coasting. My understanding is that this can cause problems and, if memory serves, the AB PowerFlex 70 has a parameter to account for this - I don't remember for sure. I'm on the hunt for that now....

Steve

 

[dmargineau]

I agree with Tom about the manufacturer choice.
A-B is somewhere in the middle.
ABB is on the top of my list when it comes to high inertia, VFD driven loads.

 

[DickDV]

Being to start into a spinning load is called different things by different manufacturers. Not sure on AB.

Look for something called Flying Start, Catch a Spinning Load, or similar.

 

[Steve Etter]

Thanks DickDV - that is the one I was looking for.

FYI - in AB its called "Flying Start En" and is described as "Enables/disables the function which reconnects to a spinning motor at actual RPM when a start command is issued."

So:

Coast to Stop
Long Accel & Decel times
Flying Start En = Enabled

Steve

 

[OkiePC]

With A/B drives, it has been my experience that using Flying Start Enable can cause a brief delay, and even a short period of (slow) reverse operation when starting from a fully stopped condition. The delay was about 1-2 seconds in my case. Make sure the blower can tolerate that before using it.

 

[Steve Etter]

Ok. Good to know.

When you say "be sure the blower can tolerate", do you have anything specific in mind? In my application, slow reverse rotation for a short time shouldn't be an issue for the overall system, but is there some kind of damage to the motor or blower itself you are thinking of?

Steve

 

[OkiePC]

Nah, in my case, it wasn't a problem either with a belt driven blower. The tensioner was spring loaded so it "didn't look right" seeing it reverse according to one of the techs watching the blower on the roof. It hasn't been a problem with that feature enabled and it has helped reduce faults when the wind is blowing (90% of the time here) and the blower is moving when starting.

On a conveyor application, however, it was a potential problem, so I had to leave it disabled.

 

[The Plc Kid]

Okie

If the drive is set to Unipolar for direction command and reverse is disabled does it still do this? It should not.

We have one where we change the revese enable / disable from the plc so it can be run in revese in the hand mode. Forward only in auto.

 

[DickDV]

Most drives with Flying Start enabled and Reverse blocked out will still find a spinning motor that is turning backward and bring it back forword. OkiePC is probably seeing the drive search forward and backward to find the motor and while doing that the motor drifts back a little too.

This would be a big problem on loads that have any kind of reverse rotation device installed, such as a sprag clutch or one-way clutch or a ratchet as on some conveyors.