"Braking" with GE VFD

you got it Tom

Now all you have to do is get more than 50 miles from home and you can be an expert on drives too! i`m just kidding you`re last post i think is right on the money Tom. I new you would get a good understanding before you were through.
(y)
 
I finished my start-up and did some testing at this site last week. I got some interesting info.

First, coast down time on the blower from full speed to dead stop with drive power removed was 7:45 (seven minutes, 45 seconds)

With the original setup the controlled deceleration was 4:30. The technician had enabled the above mentioned F41 prameter already, but I hadn't known this.

I noticed that the speed dropped to 6-10 Hz in about 2:00 and that most of the deceleration time was dropping to zero from 6 Hz.

I had the technician enable DC injection braking at 6 Hz with 10% torque and 1 second duration. He also adjusted a user prameter that is not covered in the manual that increased the deceleration torque by raising the DC bus trip voltage. The result was that the VFD could decelerate the motor from a starting speed of 55-60 Hz to dead stop in 2:00 to 2:30.

My conclusion is that the GE Fanuc VFD has less deceleration torque available as standard (that is, without braking resistors) than the Cutler Hammer and Allen Bradley VFDs. Based on experience and SWAG interpolation I would say it has about half the deceleration torque. However, with some adjustment and set up it will provide a controlled deceleration that is within the acceptable limits of my process control system.
 
It is amazing how much effort it takes to stop something as simple as AIR.

Tom, thanks for the info. It has reinforced much of what I have learned having to deal with blowers. I have set some ID fans on kiln's so they slow almost 2x the accel speed when they want to slow them. Some fans can be set to rapid decel and others need to coast.

I have been told that GE has the DC bus overvoltage trip setting on the conservative side. Most 480 volt drives are around 725 to 750 vdc.
 

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