230 motor on a 480 bus w VFD v/hz

[oceanobob]

Would like to run a five hp 230 volt three phase motor (having 6 leads) on a 480 volt three phase bus via a VFD. Have Delta and AB drives available.

Did a quick test of this idea today using one of the 480v Delta drives with these settings: 480 volts and 120 hz .... figuring the motor operating at 60 hz, given rudimentary linearity of the v/f mode, would allow the motor to receive about 240 volts at 60 hz.

Using my Fluke 87V on the VFD output (with the low pass filter mode) with the motor running with no load, the observations were as follows:
35 hz about 275 volts phase to phase
60 hz about 380 volts phase to phase

I admit this isnt what I expected, any suggestions?

 

[GoldDigger]

Was the VFD in fact configured for pure v/f mode or was it trying to do something else?
I would have expected setting a maximum output voltage limit in the VFD configuration, ruling out voltages above 240 completely.

 

[petersonra]

Try 240v and 60 hz as maximums

What model is it.

They all config a little different

 

[Jraef]

if you had the drive in SVC mode, the voltage and frequency are determined by what the drive perceives it needs to provide, so it might not be what you expect. That’s why gold digger suggested putting it in V/Hz mode if you want a predetermined ratio.

Although the drive is capable of providing 230V at 60Hz to the motor (and just program that as the others said, don’t try to get fancy), there is a risk to doing this. The DC bus voltage is not controlled, it stays the same because all the drive does is rectify the 480V to around 676VDC. So although the PWM pattern will be configured to give 230V RMS as the maximum going to the motor, each individual pulse of the PWM string will still be at that 676VDC level and that will be harder on the motor winding insulation than the PWM derived from 240V would be. So if this is a temporary solution you are probably fine, but in the long run you should plan on changing that motor.

 

[oceanobob]

Thank you for the assistance: the motor was included with a machine at an equipment sale and this is a trial of sorts directed at evaluating the machine - not purchasing a different motor at this point.

As to the inverter: best I can recall is a Delta inverter & is a model E, and yes there is more information that I will add.

In my consideration about the motor resistance & motor inductance (and admittedly not so much thinking the transient with each switching event), I had also mused about hooking up the motor leads to a wye configuration. That premise is basically this: if the delta connection is ok for 230 per the nameplate, then the wye is thumbruled as ok for 230v times (1.7) or about 390v - but that number value wasn't the 480 so this VFD v/f idea came along. And yes this 'olde thumbrule' was promulgated when clamping to line was the hookup [sans SCR/IGBT switching involvement].

Perhaps the wye hookup of the windings of this motor will be slightly more ammenable to that unavoidable peak DC bus voltage from the 480 VFD; maybe adds some resistance and as well helps with the inductance. Not as a solution but as an additional mitigation strategy against that peak.

The motor typical operational range will be around 45 to 60 hz. And as to other things such as inverted rated etc etc - cant say due to the nameplate is not inclusive of that. I can add a photo of the nameplate 'for the file'.

~~~~~~~~~~~

!! The regard of the magnitude of the DC bus casts a valid point on the issue: perhaps best to think in the terms of all the points on the pulse rather than only regarding and pondering derived numerology on a multimeter screen via a filter setting (simplified qualitative numeric value) for these factors in this particular installation.

 

[oceanobob]

After reading the responses and continuing giving the matter due consideration, decided to redo the measuring because I began to have doubts about the Low Pass Filter - upon review, couldnt be so sure.
Well, well, well: it appears the multimeter was being operated without the "Filter Mode"....because repeating the test and making sure the meter operation included the Filter and these were the readings of the motor spinning unloaded (VFD output line to line). Pls Note: The frequencies reported herein were varied from one motor to the next because we were looking at the reduction of the 480 bus voltage applied to the motor due to the V/hz inverter settings - not necessarily to compare one motor to the next.
These voltages are much closer to the expected and intended voltages; all are what was expected if the motor was operating from a 230 ish bus.

Motor A: 60 hz 240 vac, 40 hz 158vac
Motor B: 55 hz 220 vac, 30 hz 120 vac

With these readings, will leave the motor connected delta and continue commissioning w operation to follow. Readings under load will be added later once machine in operation.

Many thanks for the assistance and my apologies for the incorrect data in the original post.

 

[kwired]

Your effective RMS is where the motor would like to see, but keep in mind what Jraef mentions in post 4 and the fact each pulse can have up to a 676 VDC component within it and how well the insulation of the motor might be able to take that.

 

[oceanobob]

The life of the motor is duly noted and will be operated while the machines are commissioned and evaluated. Figuring if the machines are worthy then new motors slated as recommended per above.

Very much appreciated the assistance!

 

[winnie]

There are sine wave output filters that can be added to a drive to reduce the insulation stress caused by the normal pwm output.

Configuring a drive for reduced V/Hz reduces the output power of the drive. The drive capacity is set by output current, if you halve the output voltage you halve the output power.

Connecting a dual voltage motor for 230V and then using a 480V drive is sometimes done intentionally when motors need to be operated above 60Hz.

Jon

 

[fastline]

There are sine wave output filters that can be added to a drive to reduce the insulation stress caused by the normal pwm output.

Configuring a drive for reduced V/Hz reduces the output power of the drive. The drive capacity is set by output current, if you halve the output voltage you halve the output power.

Connecting a dual voltage motor for 230V and then using a 480V drive is sometimes done intentionally when motors need to be operated above 60Hz.

Jon

Actually Wye/Delta switching has been a thing for decades. I agree on good drives there are usually filters to protect cables and motors from PWM transients. Insulation of coil wires cares none about how it's connected, just volts. If amps, and actually more importantly heat, is managed, volts are rarely an issue.

 

[garbo]

Would like to run a five hp 230 volt three phase motor (having 6 leads) on a 480 volt three phase bus via a VFD. Have Delta and AB drives available.

Did a quick test of this idea today using one of the 480v Delta drives with these settings: 480 volts and 120 hz .... figuring the motor operating at 60 hz, given rudimentary linearity of the v/f mode, would allow the motor to receive about 240 volts at 60 hz.

Using my Fluke 87V on the VFD output (with the low pass filter mode) with the motor running with no load, the observations were as follows:
35 hz about 275 volts phase to phase
60 hz about 380 volts phase to phase

I admit this isnt what I expected, any suggestions?

Was told years ago that a 480 volt VFD set at 240 bolts output would have a frequency of 30 Hertz. Hope my old memory is correct. Of course now a a days drives have hundreds of parameters to play with. We had a very talented guy who only worked on drives for 25 years for our start ups. He had trouble on a 5 year old 100 HP drive where he had to go out to his service truck and bring back an inch thick book just on programming. He made one change on a parameter and drive worked perfectly. His company only charged maybe $200 to do a start up and this extended the free parts & labor warranty out to 3 years. I found the techs from Danfoss & Allen Bradley to be the most helpful and very knowledgeable but the largest seller of drives in USA ( or so I was told ) ABB were by far the worst. Always asked me " Why do you want to know that ". One week I had to PM over 20 ABB drives in a new building without any Manuel or training so I called ABB to ask them how to read the DC Buss voltage. Give me the run around so I sent an email, then they told me to email a different site then another wasted phone call. Took them two weeks to give me a simple answer.

 

[petersonra]

I think you can just set the motor parameters from the nameplate into the drive.

 

[kwired]

Was told years ago that a 480 volt VFD set at 240 bolts output would have a frequency of 30 Hertz. Hope my old memory is correct. Of course now a a days drives have hundreds of parameters to play with. We had a very talented guy who only worked on drives for 25 years for our start ups. He had trouble on a 5 year old 100 HP drive where he had to go out to his service truck and bring back an inch thick book just on programming. He made one change on a parameter and drive worked perfectly. His company only charged maybe $200 to do a start up and this extended the free parts & labor warranty out to 3 years. I found the techs from Danfoss & Allen Bradley to be the most helpful and very knowledgeable but the largest seller of drives in USA ( or so I was told ) ABB were by far the worst. Always asked me " Why do you want to know that ". One week I had to PM over 20 ABB drives in a new building without any Manuel or training so I called ABB to ask them how to read the DC Buss voltage. Give me the run around so I sent an email, then they told me to email a different site then another wasted phone call. Took them two weeks to give me a simple answer.

In standard modes where it would maintain volts/frequency ratio it will put out half the voltage if frequency is halved. But power is also half of what it would be at 480 volts/60 Hz.

 

[oceanobob]

The commissioning startup progress continues. Recap: motor by itself with no load ran very nicely. Fast forward to this past week when the mechanical load of the machine (not the product) was added. Not so good. Basically strange behavior but no overheating or similar. Behavior was observable surging and uneven rpm at the machine. Got a single alarm of diff types from the VFD at occasional times - ie motor overvoltage and or overcurrent. Humming sounds perhaps - but machine mechanical is quite loud. Didnt get a chance to tach it as the customer allowed minimal operation in this condition. And they were busy with changing a few parameters on the VFD (by guess and by golly) on the data entry portion of the Wizard Setup on the laptop for these drives - but to minimal avail, or if different than mentioned, a worse outcome.

Now for The Apparent Solution: I then rewired the six wire motor connection from delta hookup to the wye hookup. [added here 'for the record': The delta coil resistance was measured at 75 ohms (75. 75, 76). Neglected to measure the value once set for wye and will do so in future.] Then it was operated again and was notably improved, and once the nameplate data entry was changed to 480 and 60 hz (pls recall the idea mentioned above of 480 and 120 hz in the V/hz mode), the operation is quite fine and very smooth with measured parameters as expected for a motor operated with the machine and its mechanical loading.
Next the product load will be added to the machine mechanical load and this thread updated.
~
At this point I believe I have a 380 volt hookup (230 times 1.7 is 391) and pls recall the voltage of the bus to the VFD is 480. Perhaps this disparity will be of minimal consequence and allow decent motor life.

Much appreciated the assistance. I do wonder why did I originally involve myself with the settings and the theory of the VFD, since as far as I can discern, it appears the "olde skool hookup method" is looking like the solution. Part of the reasoning was the motor nameplate was solely denoted for a delta hookup at the lower of the usual voltages, whereas many motors (not this one) are nameplated with the two voltages - one assoc w delta and one assoc w wye.

 

[garbo]

In standard modes where it would maintain volts/frequency ratio it will put out half the voltage if frequency is halved. But power is also half of what it would be at 480 volts/60 Hz.

I sort of remember on the hundreds of drives we had that most of them were fans & pumps and at 50 % of full speed the ampere readings from the LCB ( Danfoss name for little touch screen ) were always less then 50%. Example a 480 volt 100 HP plain Jane Nena 4 pole motor usually have a nameplate of 125 amps. While running them at 50% believe ampere was usually 35 to 40 amps.

 

[Jraef]

I sort of remember on the hundreds of drives we had that most of them were fans & pumps and at 50 % of full speed the ampere readings from the LCB ( Danfoss name for little touch screen ) were always less then 50%. Example a 480 volt 100 HP plain Jane Nena 4 pole motor usually have a nameplate of 125 amps. While running them at 50% believe ampere was usually 35 to 40 amps.

Motor current is based on the load connected to the motor. In a centrifugal pump (or fan), the mechanical load expressed by the pump varies at the cube of the speed (called the “affinity law of speed”). So at 50% speed, the load on the motor is .5³, or 12.5% of what it would be at full speed. The current will be a little higher because the power factor is lower and some of the internal motor losses remain constant.

 

[kwired]

I sort of remember on the hundreds of drives we had that most of them were fans & pumps and at 50 % of full speed the ampere readings from the LCB ( Danfoss name for little touch screen ) were always less then 50%. Example a 480 volt 100 HP plain Jane Nena 4 pole motor usually have a nameplate of 125 amps. While running them at 50% believe ampere was usually 35 to 40 amps.

In addition to what Jraef said, had you increased speed of the pump current would have gone up significantly as load on the pump would have increased exponentially. wouldn't need to necessarily be by over driving the motor either, just changing gear/pulley ratio to attain higher pump speed would do it.

 

[garbo]

Motor current is based on the load connected to the motor. In a centrifugal pump (or fan), the mechanical load expressed by the pump varies at the cube of the speed (called the “affinity law of speed”). So at 50% speed, the load on the motor is .5³, or 12.5% of what it would be at full speed. The current will be a little higher because the power factor is lower and some of the internal motor losses remain constant.

Thanks. Wish just one of the many VFD Manuel's that I read in last 40 years would have mentioned the affinity law of speed. Always found VFD'S so interesting. I told all the young electricians to take an interest & learn everything they could about drives but most were not interested. One of the most amazing drives that I worked on were made by Allen & Bradley just for controlling tension on newspaper paper. While at the A&B 5 day drive class on these drives was lucky to speak to one of the design engineers. He would not tell me the price for one of these think it was 15 HP drives but told me it took 10 man years to get the program perfect. 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.

 

[kwired]

Thanks. Wish just one of the many VFD Manuel's that I read in last 40 years would have mentioned the affinity law of speed. Always found VFD'S so interesting. I told all the young electricians to take an interest & learn everything they could about drives but most were not interested. One of the most amazing drives that I worked on were made by Allen & Bradley just for controlling tension on newspaper paper. While at the A&B 5 day drive class on these drives was lucky to speak to one of the design engineers. He would not tell me the price for one of these think it was 15 HP drives but told me it took 10 man years to get the program perfect. 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.

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.

 

[garbo]

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.

Most pumps that I have came across are they two pole which provide like you mentioned around 3450 RPM. We always set minimum sorry if pumps at 20% . The only pumps that ran that slow were 75 & 100HP glycol pumps used maybe halve the year for heat recovery.