I am seeking opinions and info regarding d.c. or a.c. vector drives on a web handling application. we are considering integrating this project with either Siemens vector drives or Eurotherm vector or d.c. drives which are our current standard. I'm interested in information regarding maintenance and service pros and cons as well as opinions on their respective control architecture.
thanks for any help

 

I have used a.c drives for my web handling apps. They work nice without the need for vector control. I used 4 photo-sensors, a plc, and a drive capable of three speeds ( Faster, Fast, Slow).

A.C. drive IMHO the cheapest in the long run.

More speeds and photo-sensors can be used to reduce dancing.

Dan Boudreault

 

DC motors are a major maintenance cost compared to AC motors, need to check brush conditions periodically, also the rewinding cost of DC motor is substantial cost plus a few days for turn around by motor repair, failure of AC motor of depending on size, usually are cheaper to replace with new. Generally speaking you probably could use AC drives without going to vector drives. Vector drives and AC drives for your application were speed could be at the low end frequently might cause overheating to the motor, this issue
need to be addressed; although most drive manufacturer could recommend the motor specifications for their drives (mostly motors with H insulation, designed for AC drives). As far as trouble shooting, you need to consider
that most electricians are familiar with DC drives inside out, but AC drives and especially Vector drives you will need to consider some training cost involved just for the drives.
Finally, if you are working with fraction HP motors Permanent magnet DC motors are not much more expensive than AC motors and thus the above
arguments do not apply.
I hope this will help you on your decision good luck,
Amr Elaguizy
[email protected]

 

The main difference between scalar and vector AC drives is the fact that vector drives use two, independent control loops to control both the magnitude and direction of the motor flux. Where as the scalar drives lock together the excitation control of the magnitude and direction of the flux.

As you know, DC drives have been the mainstay for variable speed applications for sometime, especially in cases where precise speed
regulation is required. AC vector drives have improved dramatically, and in some applications function just as well as DC drives. In general, pricing for AC vector drives is competitive with DC drives in applications below 50HP, but vector drives are typically more expensive in larger sizes. As for the type of motors in vector
applications, I would consider AC motors designed for constant- torque, high-overload duty; not your standard, run of the mill AC motor.

Another important consideration is the fact that with vector drives, regeneration and dynamic braking are difficult to achieve, but not
impossible. If your application requires either, you probably would want to stick with DC drives.

Reginald Waddell, PE
Process Control Engineer
BP Amoco Corporation
[email protected]

 

AC Vector (sensorless or with encoder feedback) are as good or better as far as torque/speed performance goes - this is really the issue as far
as whether or not the drives can be applied to web handling / paper / film converting applications are concerned.

As far as cost is concerned . . . the drives are typically cheaper for DC but the motors are more expensive and are more difficult to mount due
to larger size and weight.

Maintenance . . . . brushes need attention on DC motors and they run hotter and typically come equipped with blowers for cooling. AC motors
on the other hand typically run cooler in closed loop applications because of more efficient use of current (field control is very precise in flux vector drives) and are inherently maintenance free.

Due to the above . . . we have not used DC drives in these types of applications for over 8 years. We recently retrofitted a PCMC towel rewinder with all AC drives . . . 14 in all. Handled double unwind stands, embosser - laminator drives, decorator drives, drawroll drive,
perfroll drive, bedroll drive, mandrel drives, turret drive, core load/strip drive. All motors were either open loop VF, closed loop VF and the mandrel drives were brushless AC servo motors. All drives were Control Techniques UniDrives (AC Vector, VF or Servo capable). Neat package and you need only to spare one kind of drive. For this customer, AC was the clear choice.

Thats my two cents worth. . . .

Ken Brown
Applied Motion Systems

 

Hello,

I wish to know what is exactly vector drives. Can you assist me. Your assistance and guidance is greatly appreciated. Thank you very much.


Regards,
Pirduan Sunny

 

As you know, DC drives have been the mainstay for variable speed applications for sometime, especially in cases where precise speed regulation is required. AC vector drives have improved dramatically, and in some applications function just as well as DC drives. In general, pricing for AC vector drives is competitive with DC drives in applications below 50HP, but vector drives are typically more expensive in larger sizes. As for the type of motors in vector applications, I would consider AC motors designed for constant- torque, high-overload duty; not your standard, run of the mill AC motor.

Another important consideration is the fact that with vector drives, regeneration and dynamic braking are difficult to achieve, but not impossible. If your application requires either, you probably would want to stick with DC drives.

Reginald Waddell, PE
Process Control Engineer
BP Amoco Corporation
[email protected]