×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

replace a DC drive by an AC inverter
4

replace a DC drive by an AC inverter

replace a DC drive by an AC inverter

(OP)
I need to replace a 57 KW  DC motor and its drive  by an AC motor with an AC  frequency converter, Do I need to upsize the AC motor? How much.

RE: replace a DC drive by an AC inverter

2
You need to determine maximum torque required for continuous operation and the speeds at which the torque will be required. You need to determine the maximum intermittent torque required and the duration and speed for which it will be required. Then select a VFD and VFD-duty motor combination that will provide the required torque-speed performance. Worst case operating point is usually zero-speed starting torque and minimum continuous operating speed.

RE: replace a DC drive by an AC inverter

As a rule of thumb most 3 phase, 60 Hz, 4 pole, motor/vfd combos can produce very near continuous full torque from 400 rpm to 2000 rpm.  This is called a 5:1 speed range or turn down ratio which is going to be some around 14 Hz to 68 Hz.

Many DC systems I have changed to AC had the DC motor running very slowly during operation so I had to change the gearing to keep the new AC motor in its preferred speed range.

If you need something more than a 5:1 speed range you may need to get a vector drive and vector duty motor.  There is no set terminology for the capabilities of vector drives or vector motors so read the specifications.

As CJCPE said you have to know speed and torque.  You cannot just go by horsepower.

Barry1961

RE: replace a DC drive by an AC inverter

As CJCPE has already hinted, pay particular attention to breakaway torque requirements - most DC drives have the capability to provide enormous torque at standstill if required by the load. Failing to consider it has tripped up quite a few people converting from DC to AC.

----------------------------------
  Start each day with a smile. Get it over with.

RE: replace a DC drive by an AC inverter

I would select a vector drive, rather than a volt/Hz. drive to replace the DC Drive, and would watch the breakaway torque as previously mentioned.

RE: replace a DC drive by an AC inverter

If the existing DC drive is a 4 quadrant drive, you will need to pay particular attention to the brakeing abilty of the AC Drive and motor. You may need to consider either a high brakeing torque dynamic brake resistor, or and active front end drive.
Many DC Applications that I get involved with, such as log shuttles or carriages, provide fast acceleration and deceleration in both directions.

Best regards,

Mark Empson
http://www.lmphotonics.com

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources