VFD + Boost converter wiring

T

TimothyHogan

New User
Location
Los Angeles
Occupation
Director
Hi all-

Troubleshooting a phase converter and 240>400v transformer.

The situation:
We have a european spec Kuka robot in our film studio that runs off of 400v 3phase power - which must be in a Wye.

We're powering the robot via a chinese made (I know, I know) VFD + transformer thats taking 1p240v and also upping it to the required 400v. The manual is of little help as it is 100% in chinese.

When installing, there was no clear place for the neutral, so the electrician we were working with did not wire it in. SHM. Short story - when hitting the emergency stop on the robot, the power had nowhere to go and fried a piece of our robot controller.

We're replacing the KPP (kuka power pack), but obviously need to wire the VFD / controller correctly this time!

See internals of the the transformer below. Line is coming in from the top (2 hots and 1 ground, no clear spot for neutral) , Load is going out on the bottom by the coils.

Leg to Leg the robot is receiving measured ~400v

Would the pink arrows drawn in potentially be the path for the neutral from the robot?

Note - clearly I am not an electrican, I have a commercial electrician coming in over the weekend, but trying to get as much info as possible in advance.

Let the flaming begin.




IMG_4176.jpg
 
Jraef

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
I'm allowing this since you say you are using an electrician. Normally, we don't allow DIY posting from non electrical industry professionals.
When installing, there was no clear place for the neutral, so the electrician we were working with did not wire it in.
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The electrician you used did not have a good understanding of the situation if he was looking for a "place to land the neutral". In a 240V single phase feed to a SINGLE PHASE transformer that is boosting the voltage to 400V, you would not need a neutral, just 2 lines of 240V.

THAT SAID, that transformer appears to be a 3 phase transformer! You can't use a 3 phase transformer on a single phase feed. So something in the design of this system is wrong, not at all surprising for Chinese made stuff being sent to North America. They often don't understand our use of single phase power. Either that, or someone has misinterpreted how to connect everything.

The VFD can convert single phase to 3 phase, but it cannot create voltage that is not there. So there must be a transformer to boost the 240V single phase that you have, to 400V SINGLE PHASE to feed into the VFD, then the VFD will convert the single phase to 3 phase for running 400V 3 phase motors. You cannot use the output of the VFD to feed a 3 phase transformer to then get 3 phase 4 wire output (and expect it to work correctly or for long). So either that transformer was incorrectly selected, or incorrectly applied. Sorting all of this out is not something that we can do for you from afar.

SHM. Short story - when hitting the emergency stop on the robot, the power had nowhere to go and fried a piece of our robot controller.
Click to expand...
Not sure what SHM means... but as to the other part of that, that is not how electricity works.

You really need a licensed electrician with experience in INDUSTRIAL machinery systems, and possibly someone with experience in foreign made equipment, and/or the ability to rip and replace whatever cluster-F POS the Chinese sent you.
 
petersonra

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I see a fair amount of foreign made equipment. Sometimes it takes some thought to figure out how to hook it up.

It does not seem to me that whomever hooked this up did that thinking correctly.

It is really hard to tell you what went wrong or how to fix it from your description of what went wrong, since what you think happened is not how electricity works.

Best bet is to get either an electrician or engineer experienced with this kind of thing to help you. I know that will cost more than using someone who does not know, but how many things do you want to blow up before you give in and hire the guy who knows?
 
W

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
From the description and picture I think the setup is 240V single phase to VFD to 3 phase step up transformer.

With standard components this will not work, because the VFD is expecting a motor load, and needs the motor inductance to act as an output filter.

With proper filtering, however, this setup could work.

Without a schematic of the current system there isn't much to add. Was this setup sold as a phase conversion system, or was it something hacked together by your electrician?

Jon
 
D

David Castor

Senior Member
Location
Washington, USA
Occupation
Electrical Engineer
So the transformer is connected to the OUTPUT of the VFD? If this is a standard VFD meant to be used on induction motors, I'd have real concerns about the feasibility of this. You need an inverter than can output a relatively pure sine wave into the transformer. If the transformer is on the INPUT to the VFD, I think you need a single-phase transformer, as Jeff noted.
 
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