VFD for AC Motor

I have 5 HP, 400 VAC, 50 Hz, 1750 RPM electro motor connected to gear box. Currently this motor run with DOL. We want to control the motor frequency and we plan to use AB PowerFlex 700, 5 HP. Could we connect the motor to VFD? How to define that motor is ready to connect to VFD?
Thank you
John

Generic VFD retrofit questions:

Probably the most critical question that needs answered:
How long are the leads from the drive output to the motor junction box?

What is the anticipated load? Fans and pumps and conveyors are all different and require different approaches, but all of them should be able to be accommodated.

What are the anticipated speed requirements? Running a load 50% to 100% of nameplate is much easier than 0 to 300%. Again, neither of these is a "stopper" for your application, but the motor may not be able to handle the latter speed range.

Are there space or weight restrictions near the motor or drive?

Is the motor rated for "inverter duty?"

Do you have external cooling on the motor? For long term low speed operation, you'll probably need a cooling blower.

Does your site have unusual power restrictions, such as harmonic/noise requirements in excess of normal (IEEE 519) standards? If so, what are the source impedances before the drive's location?

Tell us a bit more about what you're planning to try.

Don hit the high spots. A couple of other questions:

1) Is the load on the motor constant torque (conveyors, gear pumps, etc.) or variable torque (centrifugal pumps, fans, etc.)? This makes a difference on the VFD current rating requiremd.

2) If the motor has Class F insulation or better and a 1.15 service factor it is probably suitable for VFD use even if it isn't inverter duty rated.

3) What is the speed range? If it is a centrifugal pump, for example, you may not need anything less than 30 Hz, which makes cooling less of a problem.

Your Allen Bradley distributor should be happy to help you with the application engineering.

Is 1750 rpm correct speed of the motor for the base frequency 50Hz?

PaulB

paulB said:

Is 1750 rpm correct speed of the motor for the base frequency 50Hz?

PaulB

Click to expand...

You are right, it must be 1480 rpm.

I like continue Tom's and others explanations, lift drive mostly needs more than constant torque motor as conveyor and enough of dynamic DC-brake to stator winding when drive stop and electro-mechanical brake are still mecanically closing.

Over Hauling Load

Don and Tom covered about everything and gave you some good advice. Another thing to think about is. If the load is driving the motor while running or during stopping. If this happens the drive will trip on over buss fault. To keep this from happening you may want to add a braking resistor. You will also be able to program the drive to make a controlled stop and then set the mechanical brake. At base hz of 50 from 1480 rpms thru 1750 rpms you will be at constant hp, but your torque will be less the farther above base frequency you go because of your volts per hz ratio.

:site:

This thread is a good place to ask this question.

Where can I get some good info on the basics of variable freq drives. What I really need to get less confused on is this "constant torque" concept.
Where I get really confused is when I apply the concept to real world equipment.
EXAMPLE 1 Traction -- you don't want to apply so much torque that you spin the tires , just enough to get the bus rolling and gain speed.
EXAMPLE 2. Centrifugal pumps -- I am trying to ensure I do not confuse torque with power yet as I speed a pump up will I not need more torque?
EXAMPLE 3. Air compressors somewhat similar to pumps as speed increases will there not be a need for more torque?
EXAMPLE 4. Hoists (and maybe conveyers) again with increase speed will not torque have to increase?

Your referring me to a good source of info will be highly appreciated. At least then I will understand more and be able to ask better questions.
Dan Bentler

These give an explanation of drives and AC motors:
http://www.patchn.com/mtrwhtpaper.htm

http://www.patchn.com/what_is_a_drive.html

This offers information on motor formulas, HP, torque, slip etc:
http://www.patchn.com/motorformula.htm

HP is a reference to the work that can be done, it can be converted to watts 1HP = 746 watts 1HP is the ability to lift 33000 pound 1 foot per minute.
Torque is a reference to FORCE (rotational). Force is what creates motion.

The application is for conveyor with constant torque. Motor rpm is 1480 rpm for 50 Hz, with class F, 1.15 service factor. Conveyor operate in forward and reverse and we need to add braking resistor. The speed range is 30% to 110%.