VFD Configration

Hi,
Can we run 500v AC motor on 400V VFD? OR happened when we connect 500V input VFD and 500V AC motor with 400v supply?
Best regards,

If your input voltage is greater than specified then you could damage the inverter.

What brand and model of VFD and motor?

Assuming that your motor is designed to operate at 60Hz, then you could theoretically do this if your drive allows you to change the V/Hz ratio at which it operates, although you would never achieve the full HP rating of the motor.

Why not simply use a 500V drive and feed it with a step up transformer?

Note that VFD output voltage can't exceed input voltage. Many drive suppliers discourage putting transformers on the load side of the VFD.

However, 500 VAC is within the +/- 10% allowance for most NEMA 480 VAC rated equipment. It should not be a problem. However, as others suggest, this is a good opportunity to become acquainted with your VFD supplier by asking them to verify the application.

As Tom said, if you have 400v input, you will have a 400v output and yes, drive manufacturer is probably the best to ask about this weird configuration.
supplying a 500v drive with 400 volts may trigger undervoltage alarms if the drive couldn't be set to run with a lower refference voltage.
If the drive accept it, it's power in kw or HP would need to be downgraded to the equivalent amperage for 400v. (This is why a drive should be sized by amps instead of power)
If 500v motor is ran thru 400v out from the inverter, it's output torque and power will be reduced. Assuming P=V exp2 / R, it give me a 36% reduction if it was an heating element or a resistor. Motor exppert could comment about this as the inductive power would react differently and maybe less voltage will be compensate by more slip and more currents to bring back some torque and limit the power loss. Drive and motor max amperage capacity and thermal load cooling will limit the load anyway.

yes it will run, however only 80% of the maxpower can be used.

There is no universally applicable answer, it is totally dependent upon the specific VFD specifications. For some drive mfrs, they make a 400V "Class" drive for 380-415V systems, a 500V Class drive for 440-480V systems, a 600V Class for 550-600V systems and a 690V class for 690V systems. Nobody makes ALL of those different classes however, so everyone has different interpretations of how that is handled, if at all. The only people who can answer this question is the specific VFD mfr involved.

When diodes, transistors and IPMs are made, they test them for different maximum voltages. Because the testing for 600-690V causes the highest number of rejects and the 400V class will comprise the vast majority of demand, they leave those for last. Failed devices are scrapped, so to decrease that loss they test units for the 690V range first and if they pass, they sell those at a premium for the lower market demand of the 600-690V devices. Then they test what's left for 500V class ranges and when that demand is satisfied, they leave the rest for 400V class testing. So will a 400V class device pass for 500V or even 600V? Maybe, but it has NOT been tested for that, only because there was no need to. The demand for that high voltage class was already met before the 400V class device was tested, so it was only tested at the maximum input on the 400V class in order to decrease the losses in scrapping failed units.

But in the real world, a VFD mfr may, internally, only really buy two classes of components, 500V and 690V. They may SELL the 500V rated devices in 400V class drives at the lower price point, then take a premium for the 500V class when they can. So if YOUR drive is of that ilk, the mfr may tell you to go right ahead, no problem at all. But if your VFD mfr truly focuses on the 400V marketplace and therefor uses only the cheaper 400V class devices, they will not likely accept any responsibility for the drive being damaged by applying 500V to it.

Hi,
Thanks for all. Basically we have different voltage at different areas. Some time a 400v AC motor burnt and we have not replacement 400v AC motor while 500v spare motor available with same specification. we want to run machine with 500v motor on 400V supply VFD.

ohh in that case if you use a 500v isolated motor selected for a 400v rated power it will work just fine. We tought you were replacing for exemple a 100hp 400v with a 100hp 500v that wouldn't work well.
If you use a larger one like a 150hp 500v powered with 400v for a 100hp need, it should work well at worst, it may be a little less efficient than the right 400v one...

shooter said:

yes it will run, however only 80% of the maxpower can be used.

Click to expand...

Can you explain more? You mean that motor amps will remain as high with 400v than what it should for 500v ?
Assuming your 80% comes from (Power = V x I ) and V is reduced by 80% here, if ''I'' doesn't move, power is reduced by 80% also.
But difference with 400v motor VS 500v should be the wire lenght and size to fit under the same motor frame. Inductance/resistance? I was thinking that would affect the maximum motor torque to limit it lower than 80%?

I'm not often involved into that but i want to fill my personal knowledge so any comments on this is welcome...

This would make a 125hp 500v being okfor a 100hp 400v use

With few exceptions an induction motor will operate at any voltage/frequency that maintains the correct volts/hertz ratio. The motor torque and current will be what you expect. For example, a 380V/50Hz motor will operate just fine at 190V/25Hz. It will just be running half speed.

You can operate a motor without staying at the correct volts/hertz ratio. This is how you can run a 380/50 motor at 100Hz to double the motor speed. However, as you increase the motor speed above base speed and keep the motor voltage fixed the available motor torque decreases.

What does this mean to you. If the 400V and 500V motors are both the same horsepower, pole count and frequency then the 500V motor will only be able to run to 80% of its speed before the drive voltage limit is reached. After that you can go faster but you will lose available torque. So, as with most things, whether you can do this or not depends on alot of factors.

Keith

Some drives can go down to 400 V from 500V or 600v. Check out the Schneider Electric Altivar 61/71.

I'm fairly certain that the 600V Drive can take 400V on the input. Obviously you could push out more V since the DC bus can create a Higher Voltage but you will be increasing input current to do so. Also make sure that your drive is oversized to handle the extra current draw.