Electric motors and drives 1

[neweng2008]

Greetings,

I am a mechanical engineer with limited knowledge of electrical equipment. I need to know what is a drive that should be used with the motor I am getting on a pump. I have never seen a drive! What does it do?

Thanks.

 

[Skogsgurra]

Drive is short for drive system. It could be anything, really.

But, these days it is usually about a frequency inverter feeding an asynchroous motor aka induction motor. Some people make a difference between the motor and the frequency inverter and then the word "drive" is used for the frequency inverter.

My guess is, in your case, that "drive" means a standard frequency inverter.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Skogsgurra]

And, yes. What does it do?

It converts fixed frequency mains voltage (60 Hz or 50 Hz, depending on where in the World you are) to a variable frequency and voltage needed to make the motor turn at variable speed. A crude equivalent could be the classical belt variator. Only, the frequency inverter has a much larger speed range and a much better efficiency. And it needs next to no maintenance. A frequency inverter is also often referred to as "a VFD" where VFD stands for Variable Frequency Drive.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[waross]

If you don't know what a drive does or what it is for you probably don't need one. I am not trying to put you down, I am just a little diplomatically challenged. The majority of pumps do not use VFDs (drives) however there are more and more drives showing up on pumps.
One use of a drive is to lower the starting current on a large motor. For a pump a soft start is cheaper and will usually do the job.
A second use for a drive on a pump is to control the flow by varying the speed of the pump. This implementation is used instead of a flow control valve or in addition to a flow control valve.
In many plants a drive used to reduce the starting current would be the responsibility of the electrical department. A drive used to control flow would be either under the jurisdiction of the instrument department or a joint responsibility of both departments. The instrument department would have responsibility and control of the PID settings.


Bill
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"Why not the best?"
Jimmy Carter

 

[neweng2008]

Bill, thanks for the info. This is a repeat job so I should use the VFD. Your comment regarding the start is interesting to me. Where could I find more info on starts and their differences with Drives.
Thanks

 

[waross]

Search this forum. There have been several discussions on the topic. Don't forget to thank Skogs. If you have a serious problem in a drive he is one of the best go-to guys you will find.
Briefly;
Direct On Line starting. > Cheapest, draws up to 800% of rated running current when starting. The number of starts per hour is limited by internal motor heating. Although the starting current is less, the starting time is longer.
Soft start.> More expensive than DOL. This limits the starting current to a value that you select. Possibly 200% or 300%. The number of starts per hour is still limited by motor heating.
VFD. > Most expensive. This has the advantage of efficient speed control as well as efficiently reducing starting current. Motor heating during starting is minimal and there may be no limit on the number of starts per hour in some applications.
For more detailed information start searching.

Bill
--------------------
"Why not the best?"
Jimmy Carter