230V Nameplate motor, Running at 455V and 100Hz via VFD

[Sousterson]

I have encountered an issue on a piece of equipment that my client has purchased and plans to install in their facility. I would like to know if there is anything illegal code wise regarding what the equipment manufacturer is asking us to do. They have sold the client a submersible motor and pump that has a nameplate rating of 230V. What they are telling us is that they have been doing this for years and have had no issues. They are taking this motor and running it with a VFD at 455V and 100HZ. They have told us that they are using a Volts/Hz ratio to run this motor and run it safely at 455V even though the name plate rating is only 230V.

Can you think of any legal concerns regarding doing exactly what the equipment manufacturer has recommended? Any insight you could provide would be a great help.

 

[topgone]

I have encountered an issue on a piece of equipment that my client has purchased and plans to install in their facility. I would like to know if there is anything illegal code wise regarding what the equipment manufacturer is asking us to do. They have sold the client a submersible motor and pump that has a nameplate rating of 230V. What they are telling us is that they have been doing this for years and have had no issues. They are taking this motor and running it with a VFD at 455V and 100HZ. They have told us that they are using a Volts/Hz ratio to run this motor and run it safely at 455V even though the name plate rating is only 230V.

Can you think of any legal concerns regarding doing exactly what the equipment manufacturer has recommended? Any insight you could provide would be a great help.

That's correct. 230/50 = 4.6 and 455/100 = 4.55.

Your only problem are the bearings. Have you tried asking them if your bearings lube and bearing type are good to go with the higher speed?

 

[Twoskinsoneman]

Can you think of any legal concerns regarding doing exactly what the equipment manufacturer has recommended? Any insight you could provide would be a great help.

How do you get around

110.4 Voltages. Throughout this Code, the voltage considered
shall be that at which the circuit operates. The voltage
rating of electrical equipment shall not be less than the
nominal voltage of a circuit to which it is connected

 

[topgone]

How do you get around

110.4 Voltages. Throughout this Code, the voltage considered
shall be that at which the circuit operates. The voltage
rating of electrical equipment shall not be less than the
nominal voltage of a circuit to which it is connected

There is such a thing they called "inverter-duty" motors. You are perhaps talking about general-purpose motors. Inverter-duty motors are designed to withstand operating at lower speeds (lower voltage) without overheating and also operate at higher voltage (higher frequency) without their insulation failing.

 

[dkarst]

Your only problem are the bearings. Have you tried asking them if your bearings lube and bearing type are good to go with the higher speed?

In addition to the bearings issues are HP, you mentioned a submersible pump which is probably a centrifugal load. Operating at 100Hz vs. 60 Hz will require ~4.5X more horsepower than at rated. Hopefully, that has been taken into account. It seems to me that occasionally, submersible water pump manufacturers "push the limit" with some overload due the great cooling environment.

 

[rcwilson]

IMO there is not a code issue if the equipment is rated for 600V class. All wiring should be OK at the higher voltage/frequency. The AHJ may have a concern with the 230V motor nameplate. Additional certification or clarification from the supplier or manufacturer saying it is OK to operate at the 455V may be needed to satisfy the AHJ.

 

[Jraef]

This is a very common solution option when you want to run at high speeds for some reason. We can only assume that the pump people know all the ins and outs of this if they have been doing it for years. There is no code issue, the motor is not the "equipment" that the code is addressing, that would be the distribution and control equipment. The motor is the load, it is not switching. But the AHJ may legitimately ask for something from the supplier of the motor stating that it is suitable for this use. If they say it is, it is.

 

[T.M.Haja Sahib]

I have encountered an issue on a piece of equipment that my client has purchased and plans to install in their facility. I would like to know if there is anything illegal code wise regarding what the equipment manufacturer is asking us to do. They have sold the client a submersible motor and pump that has a nameplate rating of 230V. What they are telling us is that they have been doing this for years and have had no issues. They are taking this motor and running it with a VFD at 455V and 100HZ. They have told us that they are using a Volts/Hz ratio to run this motor and run it safely at 455V even though the name plate rating is only 230V.

Can you think of any legal concerns regarding doing exactly what the equipment manufacturer has recommended? Any insight you could provide would be a great help.

The National Electrical Manufacturers Association (NEMA) specifies that insulation systems for low voltage (<= 600 V) inverter-duty motors be designed to withstand an upper limit of 3.1 times the motor?s rated line-to-line voltage.This is equivalent to an upper limit of 713 volts at the motor terminals for a 230 V rated motor.So running the motor at 455V is no issue.Only thing to be confirmed is if it is NEMA rated........

 

[Besoeker]

The National Electrical Manufacturers Association (NEMA) specifies that insulation systems for low voltage (<= 600 V) inverter-duty motors be designed to withstand an upper limit of 3.1 times the motor’s rated line-to-line voltage.This is equivalent to an upper limit of 713 volts at the motor terminals for a 230 V rated motor.So running the motor at 455V is no issue.

I don't agree.
It completely ignores the main reason for the higher voltage insulation in the first place. This kind of thing:

This is a waveform I recorded from an actual installation. It's by no means unusual. And it's why motors run from inverters have to be designed for that duty. And common or garden motors are generally unsuitable for such applications without special precautions being taken to limit peak voltages and the extreme values of dv/dt resulting from IGBT switching.

This, as I'm sure you must know, is fairly common knowledge for those who routinely deal with variable speed drives these days.

 

[T.M.Haja Sahib]

I don't agree.
It completely ignores the main reason for the higher voltage insulation in the first place. This kind of thing:

This is a waveform I recorded from an actual installation. It's by no means unusual. And it's why motors run from inverters have to be designed for that duty. And common or garden motors are generally unsuitable for such applications without special precautions being taken to limit peak voltages and the extreme values of dv/dt resulting from IGBT switching.

This, as I'm sure you must know, is fairly common knowledge for those who routinely deal with variable speed drives these days.

Please reveal the line to line voltage rating of the motor you tested.

 

[Besoeker]

I have encountered an issue on a piece of equipment that my client has purchased and plans to install in their facility. I would like to know if there is anything illegal code wise regarding what the equipment manufacturer is asking us to do. They have sold the client a submersible motor and pump that has a nameplate rating of 230V. What they are telling us is that they have been doing this for years and have had no issues. They are taking this motor and running it with a VFD at 455V and 100HZ. They have told us that they are using a Volts/Hz ratio to run this motor and run it safely at 455V even though the name plate rating is only 230V.

Can you think of any legal concerns regarding doing exactly what the equipment manufacturer has recommended? Any insight you could provide would be a great help.

I don't know about legal concerns but I would caution against doing it for the technical concerns raised in my previous post above.
Do what Jraef has advised before puting this into service.

 

[Besoeker]

Please reveal the line to line voltage rating of the motor you tested.

It is already revealed by the waveform but I'm guessing you don't know how to read it. Anyway, it's from a 660V, 625kW motor.

Here's another particularly nasty example of a similar phenomenon on a 400V, 26kW.

There were four such motors on variable speed drives (not ours) the same site and they were dying like flies and I was asked to look at the causes.
Note the horrendous dv/dt. I calculated it to be over 3,000V/us on some of the measurements. It was killing the insulation. This sort of waveform why motors on VSDs shouldn't have bog standard insulation.

 

[T.M.Haja Sahib]

It is already revealed by the waveform but I'm guessing you don't know how to read it. Anyway, it's from a 660V, 625kW motor.

Here's another particularly nasty example of a similar phenomenon on a 400V, 26kW.

There were four such motors on variable speed drives (not ours) the same site and they were dying like flies and I was asked to look at the causes.
Note the horrendous dv/dt. I calculated it to be over 3,000V/us on some of the measurements. It was killing the insulation. This sort of waveform why motors on VSDs shouldn't have bog standard insulation.

Please note that the OP asked about the operational voltage of the VFD applicable to the motor during its operation and the corresponding insulation class for the motor,This is given by the NEMA specification which I present again to you below

The National Electrical Manufacturers Association (NEMA) specifies that insulation systems for low voltage (<= 600 V) inverter-duty motors be designed to withstand an upper limit of 3.1 times the motor?s rated line-to-line voltage.This is equivalent to an upper limit of 713 volts at the motor terminals for a 230 V rated motor.So running the motor at 455V is no issue.Only thing to be confirmed is if it is NEMA rated........

You are talking about the evil effects of standing waves due to long lead wires about which the OP did not ask and so not relevant.

 

[Besoeker]

You are talking about the evil effects of standing waves due to long lead wires about which the OP did not ask and so not relevant.

So how about you present your reasoning for the 3.1 factor specifically for inverter-duty motors?

And, just for the record, neither of the examples I posted were motors with particularly long runs. The first, from memory, was <20m. I have others similar for even shorter distances.
Have made similar measurements yourself that you could present?

 

[kwired]

Please note that the OP asked about the operational voltage of the VFD applicable to the motor during its operation and the corresponding insulation class for the motor,This is given by the NEMA specification which I present again to you below

You are talking about the evil effects of standing waves due to long lead wires about which the OP did not ask and so not relevant.

If OP concludes that it is OK to use the motor in the way described isn't this another problem that could come up, or is he supposed to wait for it to happen then come here and ask why he keeps burning out motors at that point?


My biggest concerns which have been mentioned is the higher speed that will result and the increased HP needed as a result. I suppose restriction in the discharge line could limit the load, can the moving parts handle the increased speed?

 

[topgone]

If OP concludes that it is OK to use the motor in the way described isn't this another problem that could come up, or is he supposed to wait for it to happen then come here and ask why he keeps burning out motors at that point?

My biggest concerns which have been mentioned is the higher speed that will result and the increased HP needed as a result. I suppose restriction in the discharge line could limit the load, can the moving parts handle the increased speed?

I think it is a valid concern: mechanical limits when running above the nameplate speed. That's why I was worried about the motor bearings and the grease/lube in my earlier post. Since this is a VFD, I didn't see loading a problem as VFD settings will take care of that (preset limits are always required when you configure variable frequency drives).

 

[kwired]

I think it is a valid concern: mechanical limits when running above the nameplate speed. That's why I was worried about the motor bearings and the grease/lube in my earlier post. Since this is a VFD, I didn't see loading a problem as VFD settings will take care of that (preset limits are always required when you configure variable frequency drives).

But loading is a problem. If you increase speed of a centrifugal pump and change nothing else it will require more HP which will mean more current if voltage is same. You would need to also restrict the amount of flow to reduce the amount of HP the pump will be demanding.

 

[topgone]

But loading is a problem. If you increase speed of a centrifugal pump and change nothing else it will require more HP which will mean more current if voltage is same. You would need to also restrict the amount of flow to reduce the amount of HP the pump will be demanding.

From the point of view on hydraulics, yes. I was looking at the electrical side alone. What if the motor installed is large enough to take the load at that high speed? Like I said, any VFD tech will set the limits on the motor capacity. Flow and pressure feedback could be routed to the VFD logic if the VFD control allows.

 

[Besoeker]

I think it is a valid concern: mechanical limits when running above the nameplate speed. That's why I was worried about the motor bearings and the grease/lube in my earlier post. Since this is a VFD, I didn't see loading a problem as VFD settings will take care of that (preset limits are always required when you configure variable frequency drives).

We've run motors at twice rated speed for applications such as textiles and roller tables in steel mills. This has been in the constant horsepower region - that is at rated voltage but increasing frequency. It reduces the available torque but it isn't a problem if the application can live with that. It isn't usually so unless it suits the pump curve. One of the pics I posted earlier was of a pump motor at 53Hz which was above it's nominal frequency (for here) but that got the pump to its duty point.

Cage motors are pretty robust and can usually, in my experience, tolerate running significantly above nameplate speed.

 

[T.M.Haja Sahib]

So how about you present your reasoning for the 3.1 factor specifically for inverter-duty motors?

I simply took it from the following.

NEMA Standards Publication

Application Guide For AC Adjustable Speed Drive Systems

5.2.9.1.2 Definite-Purpose Inverter Fed Motors

Per NEMA MG1 Part 31, definite-purpose, inverter-fed motors are designed to withstand maximum repetitive voltage peaks at the motor terminals equal to 3.1 times the motor?s rated rms voltage with a rise time not less than 0.1 ms. These motors can be used on a control without additional filters or reactors provided the particular combination of control and cable does not generate overshoots which exceed this requirement at the motor terminals.