VFD gives insight to process and machines 1

[fab1961]

Dear all,

for once this is not a question. Since this forum has been and currently is very helpful to me,
I would like to share an interesting experience I had.
We have been using an hydraulic pump async motor driven directly from the line.
Recently we added a VFD (for various purposes) and reading the analog output 0-10V signal
(programmed to output current drawn by the motor) we have discovered a lot of information about the process.
Nobody would connect current measuring devices just for the sake of it, while with the VFD the information
is available free of charge.
Attached an example trace we took with our CNC where the current signal has been hooked to.
Hope this may be useful to someone else. Have a nice day.

 

[waross]

With a peaking load like that you may be interested in checking the RMS loading on the motor.

43
RMS HORSEPOWER LOADING
There are a great many applications especially in hydraulics and hydraulically-driven machines that have
greatly fluctuating load requirements. In some cases, the peak loads last for relatively short periods
during the normal cycle of the machine. At first glance, it might seem that a motor would have to be
sized to handle the worst part of the load cycle. For example, if a cycle included a period of time where
18 HP is required, then the natural approach would be to utilize a 20 HP motor. A more practical
approach to these types of “duty cycle loads” takes advantage of an electric motor’s ability to handle
substantial overload conditions as long as the period of overload is relatively short compared to the total
time involved in the cycle.
The method of calculating whether or not the motor will be suitable for a particular cycling application is
called the RMS (root mean squared) horsepower loading method. The calculations required to properly
size a motor for this type of application are relatively simple and are presented in this paper.

While this is on page 43 of the document, it is on page 49 in the .pdf file.
You may find the complete paper at:

http://www.baldor.com/Shared/manuals/PR2525.pdf

Bill
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"Why not the best?"
Jimmy Carter