Not at all.
230V Nameplate motor, Running at 455V and 100Hz via VFD
- Thread starter Sousterson
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T.M.Haja Sahib
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Then what?
About what?
I don't know what you are asking.
Perhaps you could frame the question you would like me to answer more fully.
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T.M.Haja Sahib
Guest
Per NEMA recommendation,an inverter duty motor of 230V can withstand a peak voltage of 3.1x230=703V only. But per you
So it appears you are contradicting NEMA recommendation and stating that the motor needs still higher voltage rating.
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T
T.M.Haja Sahib
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Finally,I am asking you nicely,while the OP has to speak up when there is actually any derailing of his original topic,why you in an uncalled for manner enter your nose? Is it to cover up someone else's deficiencies in return for any favor?
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Please understand that standards are there for guidance and not something that gets to happen just because it is written there. On the field, values differ from what standards say it should. 3.1 is not something you hold true in any case. Understand the language of the standard and how to apply them.
As I have explained, the overshoot voltage could be 2 times the Maximum DC bus voltage of the VFD. It is a function of how fast the voltage wave that was impressed on the motor circuit and how good the motor leads can drain whatever charge was present. Nobody is contradicting anything. I understand it was a case the person actually measured based on the specific motor-VFD-supply voltage arrangement he showed.
As some mods here have said, this is not to show to other posters I could piss farther than you can! Or Bes's too. So take your chill pill. You don't know where others came from. If you learned something today, it's a good education you didn't pay for.
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T.M.Haja Sahib
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Deviation in values can occur here and there.But,in general follow the standards to your own good.
No contradiction.
So the motor insulation is made stand 713V. But your fix means that it would see more than that if operated from an inverter 460V supply.
Thus it would need higher voltage insulation*.
It's that simple.
*which it might have anyway, but would you leave that to chance?
Sousterson
Member
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- Houston,Tx
The back and forth transfer of information has been a good learning process, but the basis for the original question is should this motor that is labeled as 7.5HP 230V 60Hz be connected to a 480V 60Hz power source via a VFD. Using VFD to modify the performance of the motor to get additional HP? I have done some research and spoken with some CODE experts and I was directed to the NEC definitions of listed, labeled, identified, and approved. I was also directed to OSHA 1910.303(b)(2)
To make this even more interesting there is a certified motor test report from a pump manufacturer that this motor did perform at 455V and 100Hz for a 1 hour test on two separate occasions. So I am not denying the fact that the motor will work at a higher voltage and frequency.However, the motor manufacturer has supplied an electrical spec that states that this motor has been tested and approved in their facility at 230V hence the 230V label by the pump manufacturer.
The only way that I feel it would be acceptable to connect this equipment is to have the pump manufacturer change their labeling from only a 230V 60Hz rating, but also include 460V 120Hz rating. Therefore, if anything were to go wrong with the motor the liability is on the pump manufacturer and not on the end user client.
Installation and use. Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.
To make this even more interesting there is a certified motor test report from a pump manufacturer that this motor did perform at 455V and 100Hz for a 1 hour test on two separate occasions. So I am not denying the fact that the motor will work at a higher voltage and frequency.However, the motor manufacturer has supplied an electrical spec that states that this motor has been tested and approved in their facility at 230V hence the 230V label by the pump manufacturer.
The only way that I feel it would be acceptable to connect this equipment is to have the pump manufacturer change their labeling from only a 230V 60Hz rating, but also include 460V 120Hz rating. Therefore, if anything were to go wrong with the motor the liability is on the pump manufacturer and not on the end user client.
Sousterson
Member
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- Houston,Tx
I forgot to add that the motor only has 3 leads to connect to and not 6, 9, or 12 as one would expect for a dual voltage application.
- Location
- Massachusetts
Look out for 'B' also.............
The difference is he clearly has a grasp on the subject matter, while you clearly do not.
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T.M.Haja Sahib
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It is hard for me to believe you know anything about the subject here (you did not make any post relevant to the OP).Please do not make blind judgement.
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That is absolutely correct, I did not comment about the OPs question because I don't know about the subject. This is something you may want to consider in your own postings.
There is nothing blind about it, you have provided a wealth of information for me to come to that opinion. :thumbsup:
Kind words, thank you.
Joethemechanic
Senior Member
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- Hazleton Pa
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- Electro-Mechanical Technician. Industrial machinery
All this over 13 volts on a 700 + volt circuit?
Ok, I got to be missing something
kwired
Electron manager
- Location
- NE Nebraska
I don't think you can increase speed of a motor to gain horsepower.
If you increase the speed of a driven load it will require more power to drive the load as more work will be done.
If this motor is a 4 pole motor the syncronus speed at 60 Hz is 1800 RPM. @ 100Hz it would be 3000 RPM. If anything the pump was probably designed to operate around 3000 RPM and motor was sized for load at that speed.
Again the motor experts can clue us in hopefully. I know higher frequency means less iron core is needed but not sure if less copper is needed. If so then you probably do increase horsepower capability of same motor by running at higher voltage and frequency. This is a reason for using high frequency on aircraft - to reduce weight.
Maybe.
It isn't really about the 13V.
Variable frequency inverters use a pulse width modulated waveform to generate something about equivalent to the sine wave voltage required from the DC link voltage. It's a series of rectangular voltage pulses and the motor inductance results in a reasonably good approximation to sinusoidal current.
But the voltage pulses have fast switching edges that generate, in most cases, significant voltage overshoots.
The voltage overshoots are on top of the DC link voltage.
With a 460V ac supply the DC link voltage will be around 650Vdc. The motor insulation will see that plus tolerance plus an over voltage transient. So possibly 1400V*. Every time a pulse occurs. And that might several times a second.
This is a recognised effect. As such, motors that are driven by inverters need to have insulation that is good for this.
Inadequately rated insulation gets tired of this repeated battering and can, and does, let go after a while.
I've seen it happen a few times.
But users, and particularly specifiers, are getting better at understanding this issue.
Actually, I think I didn't write that right.
They may not understand the issue. They are just smart enough to take accept that there is one and word specifications so that it doesn't come back to bite them on their backsides.
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- San Francisco Bay Area, CA, USA
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- Electrical Engineer
Yes you can, as long as you increase the voltage at the same time. Think of HP as a shorthand notation of "A certain amount of torque at a certain speed". If you increase either value, you increase HP. The trick is to increase one without a corresponding decrease in the other. That's what happens when you MECHANICALLY change speeds, i.e. a gearbox or belt and pulley system. Speed goes up but torque goes down, or vice versa, but HP remains the same (other than added losses in the process). But with a VFD, torque is a product of voltage AND frequency, you can think of it as a V/Hz ratio. If you increase or decrease them together at the same ratio, you can change HP without changing torque. Lower is of course easy, that's what we are essentially seeing with the traditional application of a VFD. At 50% speed we are at 50% voltage, torque remains constant because the V/Hz ratio is unchanged, therefore HP is 50%. But at 100% speed and 100% voltage, you are maxed out. Since you can't make the VFD put out more than 100% voltage, any further increase in frequency begins a DECREASE in torque; we call this "operating in Constant HP mode" because with no additional voltage, you can no longer maintain the V/Hz ratio and torque begins to drop off.
UNLESS... you can continue to increase the voltage as you keep increasing speed! That's where the trick employed by the OP's supplier comes in. It's a very common issue in high speed applications to wire a dual voltage motor at the LOWER voltage, but apply the higher voltage to the VFD. Then you program the VFD to supply 100% of the motor NAMEPLATE voltage (lower) at full speed (60Hz in our case). When you get to 60Hz and start to go beyond, the VFD has plenty of additional voltage to keep the V/Hz ratio constant as you go. So if you get to 2X speed, you still have 2X relative voltage (relative to the nameplate lower voltage as the motor is connected for). When you do this, the motor is now producing 2X the rated HP! Current is still the same as it was if it had been wired for the higher voltage, so the motor is not overloaded, although there are concerns:
1) Cooling fans in the motor may become less efficient at higher speed, it depends on the fan design.
2) The bearings must be rated for the higher speed.
3) Motor rotor balancing becomes much more critical.
4) LOAD considerations become very different (as you mention below).
But if you pay heed to these issues, it really is something that we do all the time, it's no big deal.
ABSOLUTELY in centrifugal loads like pumps and fans, in fact that's the big fallacy: it's rarely economical to do this trick on centrifugal loads because the speed increases the flow, and power REQUIREMENTS of the load increase at the CUBE of the flow increase. So for example if you increase the speed of a pump by 50% (150% of design), and you did the above voltage trick with a VFD so you have 150% of the HP now, your pump LOAD requirement on the motor will increase by 1.5 x 1.5 x 1.5 or 337.5%! So if you had a 10HP motor, increasing the speed by 50% makes it a 15HP motor, but now you need 34HP to make the pump work and you overloaded that motor. So if you want to do this for some reason, you have to START with a motor that is over 3X what you need so that you get the higher flow out of it when over speeded.
One would absolutely HOPE that the pump supplier who did this was aware of this exact issue, as I pointed out above. Unfortunately from my experience, many are not. I have repeatedly come across pump salesmen who don't totally understand this issue and ask me to "just turn up the VFD speed, that'll take care of it". Hopefully that is not the case in the OP's situation. But certainly it's worth investigating.
Yes, that MIGHT be the reason they are doing this, if I recall from the OP (it's a long way back now), this was a submersible pump(?). Deep well submersibles have to deal with the issue of the weight of really long cables going down to the motor, so it might make sense to oversize the motor in order to get what you need with as little weight as possible, both for the motor and for the cable.
Again, I would hope that this is what this entire issue was all about, and that the pump OEM was/is aware of all of the ramifications etc. Some of the numbers posted in the original message actually don't work out correctly, but we don't know for sure if the OP was reading everything correctly either. Once you go "off nameplate" on something like this, it's hard to know for sure if something is an interpretation, typo, assumption or just plain incorrect.
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T.M.Haja Sahib
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Please do not start a troll on this.You accepted your ignorance about the subject.So whatever your comments about the posts on the subject discussed here are sheer nonsense.:thumbsdown:
Please don't keep doing this.
See post#35.
I'd counsel you to stay on topic and take the opportunity to learn for the heaps of information being presented here and on other threads.
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