VFD output voltage

Hi guys,

Just a quick question which is probably going to be stupid but the output voltage in the specs on these VFDs whether they be Hitachi or china-noname, is it the voltage per phase i.e. what you'd measure between each motor terminal and neutral or the delta wired motor voltage (if I've said that right..)

Here in NZ our 3 phase voltage is considered to be 400V 50hz, so I'd expect to see a VFD that has a 3 phase output to be 400V, am I reading it wrong or have I got the wrong model?

Thanks in advance
Josh

E.G...

HITACHI NES1-7SB, 1 HP, 23 VAC, 1 PHASE INPUT, VFD, With OPERATOR | eBay

The stated output voltages are phase-phase. So If you want a 400V three phase supply, you need to feed a 400V VFD with 400V. The normal way around the problem is to rewire the motor from star to delta connection. My main VFD is fed from a step up transformer, so I've got 415V three phase for my older machines, but the little Myford lathe gets 230V three phase to it's delta-connected motor from a dedicated VFD.

I haven't seen any 3phase motors for sale in NZ that are rated for less than 400V which must mean they are all delta wired is that correct?

I'm looking for a VFD inverter that will take 1 phase 240V and output 3phase 400V. Seems to be uncommon on eBay or Ali express (haven't decided to spend or go with Chinese yet).

Will I get away with the ones that say 380V output?

JoshNZ said:

I haven't seen any 3phase motors for sale in NZ that are rated for less than 400V which must mean they are all delta wired is that correct?

I'm looking for a VFD inverter that will take 1 phase 240V and output 3phase 400V. Seems to be uncommon on eBay or Ali express (haven't decided to spend or go with Chinese yet).

Will I get away with the ones that say 380V output?

Click to expand...

I don't know of any voltage doubling VFDs that will turn 240 into 415. you might find a 240 to 480v voltage doubling vfd, just as you can find 120 to 240v, and then take that vfd and reprogram it for 380v/50hz or whatever you need.

or just get a 480v vfd and re-wire the rectifier so it doubles the voltage. you could then safely run the vfd at about 30% of its hp rating.

what i recommend doing is finding a 240v to 415 vac transformer and run the transformer after the vfd. use a line/load reactor between the vfd and the transformer. add capacitors connected to the secondary of the transformer, connected Y or delta doesn't matter. you can then ground the secondary of the transformer properly. advantages are no common mode voltages which kill bearings, output is referenced to ground properly, and the increased impedance of the transformer and line load reactor means a short after the transformer will have much less chance of destroying the vfd.

disadvantages is you have to program the vfd for a linear, constant volts per hz curve which means the motor will not deliver full rated torque below 30% speed.

I've done a bit more reading and realised I'm probably getting my terminology a bit mixed up.

With regards to the spec sheet below for Hitachi VFD...


Input voltage is 1phase 200-240V 50/60hz which is fine for NZ.

Output voltage is 3phase 200-240V proportional to input, which would imply a 3phase 240V output if supplied with 240v input.

Does that mean phase to phase voltage is 240V? meaning each of the phase to neutral voltages is 138V?
Completely useless for motors in NZ that are 240V or 400V?

JoshNZ said:

I've done a bit more reading and realised I'm probably getting my terminology a bit mixed up.

Input voltage is 1phase 200-240V 50/60hz which is fine for NZ.

Output voltage is 3phase 200-240V proportional to input, which would imply a 3phase 240V output if supplied with 240v input.

Does that mean phase to phase voltage is 240V? meaning each of the phase to neutral voltages is 138V?
Completely useless for motors in NZ that are 240V or 400V?

Click to expand...

the output cannot exceed the dc bus voltage, so you can't get 400 volts ac from a 240vac vfd unless you have a transformer on the input or output or a voltage doubling rectifier in the vfd.

the output voltage of the vfd is almost always specified line to line because there is no neutral!

if you rewire your 400v motors for 240v delta then you can use them on a 240 volt vfd.

alternatively you can use a transformer to turn your 240v into 415 or 480 and drive a 400v or 480volt vfd.

some 480 volt vfds may work as low as 400 volts but i wouldn't bet on it unless it says so in the manual.

JoshNZ said:

I haven't seen any 3phase motors for sale in NZ that are rated for less than 400V which must mean they are all delta wired is that correct?

I'm looking for a VFD inverter that will take 1 phase 240V and output 3phase 400V. Seems to be uncommon on eBay or Ali express (haven't decided to spend or go with Chinese yet).

Will I get away with the ones that say 380V output?

Click to expand...

http://www.drivesdirect.co.uk/Image...NNECTION-DIAGRAM-WITH-REV-OFF-FWD-+-SPEED.jpg

I'm happy to wire it for 240V delta if that would work.

Going off track and to help get my head around this... I pulled an old conveyor belt motor out of the loft and on the plate it says 380V Y, and 220V delta.

If in NZ our 3 phase supply is 400V (or lets call it 380V), does this mean I can only wire this motor in star configuration? If this is true, the motor is decades old before VFDs were around (I'm assuming) why does it even have a delta configuration, where would you have got 3phase 240V from in NZ?

JoshNZ said:

why does it even have a delta configuration, where would you have got 3phase 240V from in NZ?

Click to expand...

NZ wasn't on the leading edge of setting voltage standards. from what i know its mostly the american market that ended up with 240/480v motors, where the rest of the world ended up with Y/Delta motors.

Awesome link Rons thanks for that.

I've found a motor on a local auction site, have attached the plate below here.

<IMG>https://www.practicalmachinist.com/vb/attachment.php?attachmentid=231446&stc=1&d=1529818481</IMG>

Are all three statements here true?
1- I could run it at 240V/25Hz in star configuration as Rons article suggested,
2- I could wire it in delta and run it on the 240V output of the Hitachi VFD above
3- Without a VFD, there would be no way to connect it to NZ 3 phase power in delta configuration.

And the photo this time... Edit function not working?

JoshNZ said:

I haven't seen any 3phase motors for sale in NZ that are rated for less than 400V which must mean they are all delta wired is that correct?I'm looking for a VFD inverter that will take 1 phase 240V and output 3phase 400V. Seems to be uncommon on eBay or Ali express (haven't decided to spend or go with Chinese yet).Will I get away with the ones that say 380V output?

Click to expand...

Josh,In my experience, any three phase motor sold in NZ in the last 40 years or more can be run on either 230 or 400 volts.As long as there are 6 terminals, you should be OK.The attached wiring diagram shows a typical NZ three phase motor, the "delta low-voltage" diagram on the left is for 230 volts, the "Star High-Voltage" diagram on the right is for 400 volts.Also a typical NZ three phase motor plate showing the 230/400 volt options.If you buy a VFD with single phase input, you configure your terminals for Delta and it will run happily on 230 volts three phase.If you buy a VFD with three phase input, you configure your motor terminals for Star and it will run on 400 volts three phase.If you configure the motor for Delta and supply it with 400 volts you will burn the motor out in a few minutes.If you configure the motor for Star and supply it with 230 volts, it may run, but have hardly any power.Some older NZ three phase motors only have "three wires" and can only be run on 400 volts three phase. The other three wires will probably be somewhere inside the motor, but you don't want to get into that.BTW, USA three phase motors usually have 9 terminals, so their terminology and descriptions can be confusing.I am not an electrical expert, but have used VFD's for years, the above has been correct for the usual motors we come across e.g. geared motors for conveyors etc.Let me know if you need anything clarified, or if I have got anything wrong!

Josh, the edit function is not working for me either and it is also compressing the text into a single block In my post above I described using Delta or Star. I am referring only to the NZ diagram I attached. Look at the bottom of the page for the correct "Motor Terminal Block" configurations.Don't use any USA diagrams you may find as they are not the same as our motors.

Thanks heaps Peter. That clears up my confusion.

Next question is how do you get them in NZ haha. I went to go through with that Hitachi and it wants to out $100 of import tax on the sale .

Josh,
I don't know why the seller is charging you import tax. If you have too much trouble, I can recommend YouShop which is a service run by NZ Post.

You buy the item on E-bay and give the seller the USA address for YouShop. So you are only paying US postage charges (I estimate US$19 using the YouShop Zip 97203). Then YouShop consolidates your parcel with others and ships it to NZ and finally posts it to you.

You will probably have to pay GST once it arrives in NZ, which is $39 on NZ$260.

I worked out the YouShop charges for posting the VFD - I think they would charge you NZ$30 (Economy option) to send from US to your place in NZ. (or more if the parcel is much larger than the VFD dimensions given) It can take a couple of weeks, so no good for urgent stuff.

In this case, the seller quotes a shipping charge to NZ of NZ$72 which may be similar to using YouShop, but hopefully you would avoid the "import tax" or whatever it is the seller is trying to charge you.