Variable Speed Drive - Frequent ON/OFF 3

[PoliPoliCarps]

Dear All,

Can I ask, are there any serious effect or what happens when you frequently ON / OFF a variable speed drive? will something happen to this equipment?

Thanks

 

[Ethnan]

Variable speed drives are designed for constant change of speed and not constant turn off and on. When you constantly turn on/off a VSD motor,you put electrical stress on the power supply circuit, in form of high starting current during turn on, and high surge voltage during turn off. If your power circuit has the necessary snubbers and flywheel diodes to clamp these surges, then you are fine. Its possible the VSD drive already has these inbuilt circuitry to handle such.

 

[itsmoked]

IT will fail prematurely. It will say all over the manual not to do this. A lot goes on when you throw the power to a drive. Once a day is about the most you want to cycle them.

Why would you need to cycle them more? If you want it off for safety then use the Safe Torque Off (STO) feature correctly.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[LionelHutz]

Yes, it will blow up prematurely.

Cycling too quickly means the bus charging circuit doesn't have time to reset and the bus tries to charge without any current limiting. Someone will cycle it this quickly if you build a setup that allows the power to be cycled on and off.

 

[BrianPetersen]

Original poster needs to clarify the situation:

(1) Are you proposing to switch incoming power to the drive on and off using external contactors frequently (bad), and if so, are you proposing to switch power on with a simultaneous motion command and/or with the motor still spinning (coasting) from the previous switch-off (extra-bad)? Are you proposing to switch power off using contactors in the incoming power if the motor is still turning, or even under power (extra-really-bad)? All of these are asking for the magic smoke to come out. The other thing that you haven't told us, is whether this is a little 1/2 horsepower motor with next to no inertial load, or a 75 horsepower motor driving an enormous gearbox with a huge inertial load. It makes a difference. A little motor with next to no inertia, you can get away with stuff that a big one won't let you get away with.

(2) Or, are you proposing to leave incoming power to the drive, but switching the motor on and off using "drive enable" or the designed-in motion-enable and motion-command inputs, and allowing the drive to ramp motor speed up and down smoothly? This is OK - this is what they are designed to do.

(3) Is the situation safety-related? If it is, use a drive that has integral "safe torque off" as mentioned in a previous post. Use your safety and non-safety logic in conjunction to do this properly (easiest with a PLC and safety PLC). You may in some situations when there is a protective-stop condition, have to do a controlled stop by ramping speed down and then opening "safe torque off". The smart person in charge of the risk assessment for the machine needs to be aware of this and potentially have their input on this.

(4) Is the situation safety-related and you are using an old clunker of a drive that doesn't have STO? Or you are using a new drive that has it, but the rest of your control system isn't smart enough to handle it properly? Good luck. Again, the smart person in charge of the risk assessment needs to be aware of this and potentially have their input on this.

 

[jraef]

Brian is correct, you need to clarify what you mean. Cycling power often = premature failure. Commanding a Run can be done to the limits of the motor.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[PoliPoliCarps]

Hello there.
Thank you so much for responding to my question.

Here's some information.

The operation is a Mining Plant.
I have Two Motor Feeders rated 250kW with belt to feed the material to the next operation which is the Crushers
This Two Motor Feeders 250kW coupled together with a hollow shaft and a torque arm.
these are running being run using the VSDs G150 Siemens.

Now, the operation.
When BIG ROCKS are FEED to the HOPPERS, the Feeder Drives will then run to feed it but however there are timmes that the crushers are still CRUSHING some very big rocks and not yet finished. So the Motor Feeder Drives run by VSDs need to stop to avoid many ROCKS inside the CRUSHERS and Overload it.

Now, here they frequently stop the Motor Drive and start again after the Crushers finished it crushing big rocks.

 

[davidbeach]

Don’t stop the drive, just set the speed to zero. Stop the motor, not the drive.