230 motor on a 480 bus w VFD v/hz

[MD Automation]

They had a device to pick up the speed of expiring roll of paper that could be traveling over 40 MPH and have the incoming 3,000 # roll of newsprint perform a speed match then make a splice by double sided tapes and cut it. This was 30 years ago when they still were printing a lot of newspaper.

That kind of synchronized motion matching software is always the most interesting stuff to me (I'm an engineer working a lot with servo drive applications). It's relatively easy to do simple synchronization with modern equipment, but it would have been real interesting to see how they worked out a complicated process on something like you saw 30 years ago! To perform a paper splice "on the fly", between 2 different rolls, at those speeds...pretty neat.

Applications like a "winder" are very cool to watch - how they keep track of the tension on the product as well as the size of the spool (as it changes with winding / unwinding, the speed of the product will change unless you keep adjusting the spool rpm).

 

[Jraef]

Kind of a rule that applies to the pump whether you have a variable speed power source or not.

Take ae pump that was designed to be driven at 1750 RPM and connect it to a 3450 RPM motor and you will overload the motor in most instances because of the way the load increases with speed.

Do the other way around by putting the 3450 rated pump on a 1750 rpm motor and your flow will be well below what was expected, but probably could have used 1/4 or 1/3 size of motor to drive it this way.

I’ve even run into it when people buy some machine cheap from China that has a 50Hz motor on a pump, then connect it here and the motor overloads. That 20% increase in speed means the pump needed 173% of the Hp!

 

[garbo]

That kind of synchronized motion matching software is always the most interesting stuff to me (I'm an engineer working a lot with servo drive applications). It's relatively easy to do simple synchronization with modern equipment, but it would have been real interesting to see how they worked out a complicated process on something like you saw 30 years ago! To perform a paper splice "on the fly", between 2 different rolls, at those speeds...pretty neat.

Applications like a "winder" are very cool to watch - how they keep track of the tension on the product as well as the size of the spool (as it changes with winding / unwinding, the speed of the product will change unless you keep adjusting the spool rpm).

One other interesting thing about the specialized newsprint drives we were told that most times they act as a brake to keep constant tension on paper. The larger motor in on each print unit had a larger motor. Constant tension was critical when running color pages because they had to pick up colored ink from two separate print units that paper could be any where from 12 to over 30' feet away. Worked at Whitman Chocolates where they had a 10 miillon dollar state of the art 200' long machine that inserted 8 pieces of chocolates covered candy into a moving box. Had we were told synchrous motor for drive conveyor & 6 pick & playoff stations. If arm was off more then say 1/8" it would crash cardboard box. Machine on a goid day placed over a million pieces of candy in 8 hours in the 1 # Sampler boxes. Never came across an encoder. Each of the 7 motors were on drives that were totally immersed in oil. They used a proximity switch to detect where each pusher lug was on pre stretched drive chain.

 

[GoldDigger]

In the case of submersible well pumps in particular, the bearings rely on hydrostatic/hydrodynamic pressure effects instead of an oil layer to separate their surfaces. Running below a certain speed for any length of time can destroy the bearings.

 

[Phil Timmons]

Back to the start -- the OP seemed to wonder why the Voltage was brought down with the Frequency?

Yes, that is a correct observation and the general intent.

If you think about the general equation -- V = Amps X Resistance . . . . that is generally for simple DC, but we use it also with steady state (typically 60 HZ) AC.

More specifically the AC version is V = Amps X Impedance, or V = A x Z. Since Z varies by frequency across a set "Coil" (motor winding) Z tends to reduce towards Zero the lower the frequency goes.

So IF frequency goes down, with a set motor winding, the Z also goes down. So a VFD is generally designed to lower the Voltage, as well -- to also keep the Amps down, or else the motor winding would toast as the Amps would keep increasing.

 

[oceanobob]

As the OP, this issue has certainly raised a couple questions - the first one was about the readings and that one was answered when I figured out I needed to use the low pass filter feature on the Fluke 87.

But after that was done on the freewheeling motor and the readings were as expected with the V/hz programming, a mechanical load of the machine was added to the experience, the motor and the AB powerflex combination protested the install by surging and making weird humming sounds - that question is not able to be answered .... so, in a sort of desperation, I changed the wiring from delta to wye and changed the AB 'program' to 480 volts and 60 hz (the usual settings for these VFDs) and the motor responded nicely: No surging & No weird humming sounds.
Making me wonder why I bothered with the programming idea of 480 and 120 hz. Wont know if the delta drive can do - cause the equipment owners prefer AB. But until the motor can successfully operate the mechanical machine load with the product load, the final arrangement will not be known and which we are awaiting the commissioning process as they add the product .... to learn if this will be the answer.

The delta drive software has a graph with defined points to help with the determination of the settings and where in the program to place these values ~ whereas the AB Powerflex software wizard simply has a table that allows the nameplate information to be entered - but no graphical interface like the Delta software includes.

I prefer the idea of a graph with a line having a point at 480 and 120 crossing through 240 and 60 (halfway up the graph) ~ as opposed to the delta wye wiring swap 'cause the delta to wye voltage ratio pivots on the value of 1.7 and not 2. Using 1.7, the wye should be optimum at 240 times 1.7 or around 400 volts - and not 480 volts.

But if I can't use the AB Poweflex VFD to more accurately provide the requisite voltage at the desired frequency - I will resort to the olde school method of motor lead swapping the connection from delta to wye.

As soon as I find out if the motor can perform I will certainly update this post.


Thanks to all for the assistance and to the good, it was learned the DC bus on a 480 drive is way higher value than the DC bus on a 240 or 208 drive. That is indeed a consideration to be taken under advisement.