brought to you by Pumps & Systems

Vector Drive Webinar Q&A #4

I had heard of one pump company promoting an open loop vector drive as delivering 100:1 turndown. Possible?

Permalink Reply by Michael Dillon on February 26, 2009 at 2:57pm: Glenn, John and I are all agreed that this is not likely. If they are, then the base speed of a four pole motor has to be around 6,000 rpm. That is possible but over 100 Hz the motor characteristics get real strange and a little unpredictable. This may be something more commonly used on a variable torque application like a centrifugal pump or a fan. Speed stability will be an issue above 3000 rpm on the 4-pole motor.; ▶ Reply to This

Permalink Reply by Glenn A. McIntyre on February 26, 2009 at 6:18pm: When you get above base speed, the motor is generally good for constant HP up to around 90 Hz. The torque begins to drop off rapidly as the speed increases above 90 Hz. With a constant torque load like a positive displacement pump, the motor would need to be significantly increased to produce the required torque at the high speed.

Saying you can operate the motor over a 100:1 speed range is fine, but practical operation at the high speeds required is another story.; ▶ Reply to This

Permalink Reply by ADITYA RANJAN PATHAK on March 26, 2009 at 10:14pm: In general, any rotating equipment operating far from the design point will result in lower efficiency and loss of efficiency is converted into heat, noise, vibration etc.
Moreover, at low rpm, the heat dissipation is not proper. It measn that motor has to be oversized to take care of additional possible heat dissipation requirement.
At higher rpm, torque starts decreasing.
Therefore, so high turndown (100:1) is impractical.; ▶ Reply to This

Permalink Reply by Bob Feltman on June 1, 2009 at 8:03pm: Michelle, I don't have the answer to this but I know someone who might Ben Ewing Drive Specialist with WEG Electric Motors. I've asked him to address the issue.; ▶ Reply to This