Abdou Barrow recently had to re-assemble a WEG MV01 medium voltage VFD that had been taken apart at a distant site, and then commission the VFD. The following is his account of this unusual call.
I recently did a start up on a 3000 HP 4160 volt WEG MV01 medium voltage VFD in California. (IF you require service on a medium voltage VFD, hit the live support chat icon, or call your nearest EMA facility (see bottom of page) OR, hit the contact icon on the top right)
This VFD was acquired through acquisition of a company that was operating the medium voltage WEG VFD in Michigan. The WEG medium voltage VFD was disassembled for shipment in Michigan, by a contractor that was not available to reassemble it.
So we were faced with a bit of a puzzle; we had to reassemble a complex and expensive medium voltage VFD, when we were not there during dis-assembly. Mistakes can be very costly on any medium voltage drive, but to make matters worse, this particular medium voltage VFD was rated for a 13.8 KV input, and a 4160 volt output.
We discovered this by talking to the customer prior to arriving on site. The customer had assumed that it required a 4160 volt input, and didn’t have 13.8 KV available. We assisted him in procuring the proper transformer.
A typical medium voltage VFD start up requires megging the medium voltage phase shifting transformer and motor. The power wires also have to be hi-potted on new applications. This is very important to prevent extensive damage to the VFD and potential harm to personnel.
In addition to the electrical issues, there were mechanical issues, involving assembling the different sections of the MV VFD. I took the job of doing the internal electrical wiring of the VFD myself to make sure that there were no mistakes in both the wiring and the fiber optic cabling. There was minor electrical damage to the equipment during transit, and I was able to repair it.
After a week of labor putting the medium voltage VFD, input transformer, and switchgear all together we ran into a delay in getting the medium voltage rated cables. Despite this delay, we were able to get all the internal electrical and fiber optic connections finished. I performed a low voltage test on the WEG medium voltage VFD. This is very important step of starting a WEG MV01 MV VFD.
The WEG MV01 MV VFD uses the low voltage VFD type topology in its pre-charge network with some exceptions. The MV01 MV VFD uses three phase 460V input and generates 4160V using an internal transformer. The WEG MV01 uses two stages of pre-charge networks just like in low voltage VFDs. Once the 1st and 2nd stage pre-charging is finished and the handshake between the switchgear and the MV VFD is normal, the VFD will allow the switchgear to close and put medium voltage to the MV VFD.
This handshake is very important, for if the pre-charging is not complete, and the switchgear closes, damage to power components and harm to personnel can result. The low voltage test is essential to verify that the handshake between the MV switchgear and the WEG medium voltage VFD is all set before even connecting the power wires from the 13.8KV feed to the input of the switch gear. Once the handshake was verified, I was comfortable with allowing the electrician to wire the 13.8KV to the input of the switch gear.
With just the 460V input, I was able to charge the bus to 5000V and bump the motor and check rotation. This also gives me assurance that the firing circuits are working properly. If there were firing issues on the power arms, I would have fault indications from the MV VFD. Since this particular WEG MV01 VFD ran the motor before, I simply verified all the motor data was accurate.
I also did calibration testing of the power arms and the temperature feedback boards on the VFD. All the tests came out normal.
The final stage of the start up was to bring in the 13.8KV through the phase shifting transformer to the MV VFD. As explained earlier, this is accomplished automatically when the VFD “Power on” button is pressed and the handshake between the MV VFD and the switch gear is good. After pressing the “Power on” button in the front panel of the WEG MV01, the VFD went through the 1st and 2nd stage pre-charging and closed the switch gear. This allows the medium voltage to be applied to the WEG medium voltage VFD. At this point I verified that the bus voltage level and other status indications were normal and then started to perform a test run of the motor. After 30 minutes of testing with no load, I released the MV VFD back to the customer to run production.
This particular medium voltage VFD is used on a motor that runs a pump used in desalinization.
EMA repairs and services not only WEG medium voltage VFDs, but on Siemens Robicon Perfect Harmony medium voltage VFDs, Toshiba T300MVi medium voltage VFDs, TMIEGE medium voltage VFDs, and the Allen Bradley Powerflex7000 medium voltage VFD. Call your nearest EMA location should you need help on your MV VFD.
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