# Motor current unbalance?



## ace24wright (Jul 10, 2012)

tates1882 said:


> I have a 5hp 3 phase 208v motor that is fed from a Yakawas VFD. I have a unbalance of 2amps on C phase when compared to A or B. The FLA is 13.9 amps and the motor is actually pulling 14.2 on A, B but on C its 15.9. Motor is brand new. Doesn't the VFD correct any voltage imbalance from the incoming before its makes it to the motor? The drive keeps tripping out on an overload fault but A, B phases are below the OL setting only C is above. The 5hp motor is slightly overloaded but within the service factor of 1.15 and I think a 7.5 would be overkill. Anyone have any Ideas?
> 
> Also the drive steps the voltage up to 250 @ 60htz so should't the FLA in turn go down?


 what did the motor ohm out?


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## JRaef (Mar 23, 2009)

You are correct about the drive isolating any line imbalances from the motor. There is no connection. The VFD is in essence a brand new source of power that just uses the line as a raw material to make it. So if you truly have an imbalance on the output, that would indicate a problem in the motor, i.e. your winding insulation is failing.
How are you reading the voltage and current? Most common VOMs, even those that claim "true RMS" are incapable of accurately interpreting the complex waveforms on the output side of a VFD. I caution people against trusting what they are reading with a typical Fluke meter. The ones I would trust are those that start at about $3000, not something the average electrician needs to outlay unless planning to do a lot of VFD troubleshooting.
The VFD cannot put out 250V on the output unless you give it at least 250V on the input. It cannot create voltage that is not there. If your meter is showing 250VAC, that is another indicator that your meter is incapable of interpreting the PWM output.
If you do have 250V available and the VFD is programmed to put out 250V at 60Hz, then your motor current will NOT go down, it will actually go up. A motor rated for 208V on the nameplate is either a 208/230V dual rated motor, or it is actually a 200V rated motor. If it does say 208/230V on the nameplate, 250V is the upper edge of its voltage tolerance, but you are pushing it close to saturation. But if it is a 200V labeled motor, you are 20% over voltage and you are saturating the windings, which raises the temperature, current draw and torque damage risk. Reprogram that VFD to put out motor nameplate voltage at nameplate frequency, anything else risks motor loss.


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## mrmike (Dec 10, 2010)

The above response is just great, but it may be too late for your motor. Sounds like it-and if you saturated the windings enough, it will be damaged, even if it is new..........why is this drive/motor undersized? Is there more load because of a mechanical fault? Lots of times we have these and we fool with the drive instead of looking at the load and end up with this senario...........


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## tates1882 (Sep 3, 2010)

JRaef said:


> You are correct about the drive isolating any line imbalances from the motor. There is no connection. The VFD is in essence a brand new source of power that just uses the line as a raw material to make it. So if you truly have an imbalance on the output, that would indicate a problem in the motor, i.e. your winding insulation is failing.
> How are you reading the voltage and current? Most common VOMs, even those that claim "true RMS" are incapable of accurately interpreting the complex waveforms on the output side of a VFD. I caution people against trusting what they are reading with a typical Fluke meter. The ones I would trust are those that start at about $3000, not something the average electrician needs to outlay unless planning to do a lot of VFD troubleshooting.
> The VFD cannot put out 250V on the output unless you give it at least 250V on the input. It cannot create voltage that is not there. If your meter is showing 250VAC, that is another indicator that your meter is incapable of interpreting the PWM output.
> If you do have 250V available and the VFD is programmed to put out 250V at 60Hz, then your motor current will NOT go down, it will actually go up. A motor rated for 208V on the nameplate is either a 208/230V dual rated motor, or it is actually a 200V rated motor. If it does say 208/230V on the nameplate, 250V is the upper edge of its voltage tolerance, but you are pushing it close to saturation. But if it is a 200V labeled motor, you are 20% over voltage and you are saturating the windings, which raises the temperature, current draw and torque damage risk. Reprogram that VFD to put out motor nameplate voltage at nameplate frequency, anything else risks motor loss.


 2. A fluke 289 and 179. Both the DMM and Drive LED show 250 Vac when the drive is fully up to speed . The motor is a 9 lead 230/460 vac. It should be good up to 253vac. When I programmed the drive I set the base voltage at 208 and the base frequency at 60htz.


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## tates1882 (Sep 3, 2010)

mrmike said:


> The above response is just great, but it may be too late for your motor. Sounds like it-and if you saturated the windings enough, it will be damaged, even if it is new..........why is this drive/motor undersized? Is there more load because of a mechanical fault? Lots of times we have these and we fool with the drive instead of looking at the load and end up with this senario...........


Well the motor is part a 5 motor water source heat pump system. I have 2 5hp motors running a closed loop circulation inside the building, 2 7.5 hp running sump pumps for the outside loop and a 5hp running the evap. tower. 

The inside loop has no valves, just a plate exchanger. When the maintenance tech took this place over 10 years ago he said that they had 3hp motors on the loop and they were smoking atleast 1 per year. So he up sized to 5hp and I think they are still overloaded. I can adjust the water flow to back down the current but then heat builds in the water and the heat pumps shut down with a high head pressure fault.


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## JRaef (Mar 23, 2009)

tates1882 said:


> *I have a 5hp 3 phase 208v motor* that is fed from a Yakawas VFD.
> 
> ... *The motor is a 9 lead 230/460 vac.* It should be good up to 253vac. When I programmed the drive I set the base voltage at 208 and the base frequency at 60htz.


Which is it, a 208V motor or a 230V motor? What is your line voltage, 250VAC? If so, why would you program the drive to deliver only 208V at 60Hz? You would be starving it for voltage, losing torque. Either you have a 208V supply and your meter readings are incorrect, as I suspect, or you have a 240V supply that is climbing to 250V but are doing something strange here that I do not understand by programming the drive to deliver a lower voltage. As I said, a VFD cannot create voltage that is not there, so it cannot put out 250V if it is only getting 208V in, or even 230V in. 

As to loading, was this system designed overseas by any chance? Because a common problem is that packaged pump systems are designed expecting 50Hz operation, then they get here are people reprogram them for 60Hz. Your motor, being 230/460, appears to be a NEMA motor, but was it changed out when it got here? Because on centrifugal pumps, the flow, and thus the LOAD ON THE MOTOR, goes up at the cube of the speed change. So at 120% speed, the motor load becomes 171% of what it may have been designed for. If the motor was changed out from a 50Hz design, it would have needed a larger motor to run the same pump at 60Hz. Worth checking out. The clue is that you said you can reduce the flow and bring the current down, that indicates that your problem may be not enough HP for the flow you are trying to get out of it.


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## nolabama (Oct 3, 2007)

^^^ wow.


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## JRaef (Mar 23, 2009)

Actually, forget the stuff about being designed overseas. I hadn't thoroughly read that other post and didn't notice that you said he had already up-sized it to 5HP. That should have taken care of it if that was the only issue.

Might still be under sized though. If you reduce the flow so that the motors are not running overloaded, but then you are not getting enough flow to cool the water, that indicates the entire cooling tower is not adequate.


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## ilikepez (Mar 24, 2011)

JRaef said:


> You are correct about the drive isolating any line imbalances from the motor. There is no connection. The VFD is in essence a brand new source of power that just uses the line as a raw material to make it. So if you truly have an imbalance on the output, that would indicate a problem in the motor, i.e. your winding insulation is failing.
> How are you reading the voltage and current? Most common VOMs, even those that claim "true RMS" are incapable of accurately interpreting the complex waveforms on the output side of a VFD. I caution people against trusting what they are reading with a typical Fluke meter. The ones I would trust are those that start at about $3000, not something the average electrician needs to outlay unless planning to do a lot of VFD troubleshooting.
> The VFD cannot put out 250V on the output unless you give it at least 250V on the input. It cannot create voltage that is not there. If your meter is showing 250VAC, that is another indicator that your meter is incapable of interpreting the PWM output.
> If you do have 250V available and the VFD is programmed to put out 250V at 60Hz, then your motor current will NOT go down, it will actually go up. A motor rated for 208V on the nameplate is either a 208/230V dual rated motor, or it is actually a 200V rated motor. If it does say 208/230V on the nameplate, 250V is the upper edge of its voltage tolerance, but you are pushing it close to saturation. But if it is a 200V labeled motor, you are 20% over voltage and you are saturating the windings, which raises the temperature, current draw and torque damage risk. Reprogram that VFD to put out motor nameplate voltage at nameplate frequency, anything else risks motor loss.


So meters with low-pass filters aren't really good enough to get a proper reading off a vfd?


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## tates1882 (Sep 3, 2010)

JRaef said:


> Which is it, a 208V motor or a 230V motor? What is your line voltage, 250VAC? If so, why would you program the drive to deliver only 208V at 60Hz? You would be starving it for voltage, losing torque. Either you have a 208V supply and your meter readings are incorrect, as I suspect, or you have a 240V supply that is climbing to 250V but are doing something strange here that I do not understand by programming the drive to deliver a lower voltage. As I said, a VFD cannot create voltage that is not there, so it cannot put out 250V if it is only getting 208V in, or even 230V in.
> In coming line voltage 208v 3p, the motor is a design code B class H, 60htz, 208v/230/460/ 9 lead delta start/ delta run. I checked voltage at the overload terminals and at the motor, with a fluke 179, 289, and the maintenance techs Ideal. Plus the drives LED was displaying 250v, the same as all three DMMs. Even with the parameters for voltage set at 208v the output voltage at the OL and motor are about 220v.
> As to loading, was this system designed overseas by any chance? Because a common problem is that packaged pump systems are designed expecting 50Hz operation, then they get here are people reprogram them for 60Hz. Your motor, being 230/460, appears to be a NEMA motor, but was it changed out when it got here? Because on centrifugal pumps, the flow, and thus the LOAD ON THE MOTOR, goes up at the cube of the speed change. So at 120% speed, the motor load becomes 171% of what it may have been designed for. If the motor was changed out from a 50Hz design, it would have needed a larger motor to run the same pump at 60Hz. Worth checking out. The clue is that you said you can reduce the flow and bring the current down, that indicates that your problem may be not enough HP for the flow you are trying to get out of it.





JRaef said:


> Actually, forget the stuff about being designed overseas. I hadn't thoroughly read that other post and didn't notice that you said he had already up-sized it to 5HP. That should have taken care of it if that was the only issue.
> 
> Might still be under sized though. If you reduce the flow so that the motors are not running overloaded, but then you are not getting enough flow to cool the water, that indicates the entire cooling tower is not adequate.


No not from overseas installed in 94. The original motors were Baltor 200v 60htz 15fla maybe design B 5hp. They were swapped 11years again when the maintenance tech took over. He said he upsized them from 4hp to 5hp because of water hammer and start up trips. He had the original ones stuffed in a corner, he showed me them yesterday. So they were never upsized. The newest motor he installed after I retro'd the MCC and added 4 VFD's. (We talked about the retro in another thread.) Currently the OL on the VFD's is disabled and the motors are on manual OL's running at the limit of there service factor. The tech has two backups and he wants to "run them till the magic is gone," then up grade to a 7.5hp. All the motors are within 10 rpm of each other.


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## Gbart (Aug 22, 2012)

I would recomend checking all connections to the motor first, this includes the drive and the motor itself. It could be as simple as a loose connection. 
If the drive is a bypass drive run it in bypass and check the amperage.
Another simple test is to megohm the motor to see if you have widing issues.
If it is not run direct power to the motor, at least then you will rule one or the other out.
Did a certified Yaskawa rep do a start up on the drive? There are several parameters that need to be set including Auto Tune which tunes the drive to the motor. You also extend the warentee by 2 years.
Last but not least these new drives are DC inverter drives not the old chopped reformed AC drives. The DC bus voltage would be as high as 250.
Hope that helps!


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