Upon receiving a call from my maintenance team requesting assistance with a non-operational PowerFlex 70 drive, I quickly assessed the situation. Upon arrival, I discovered that they had mistakenly connected the incoming 480 volts to the wrong terminals. Despite this error, I determined that there was no visible damage to the drive. By simply swapping the leads, we were able to successfully power on the drive without any issues. Surprisingly, the diodes in the drive remained undamaged. This led me to wonder if the reverse current of the diodes was robust enough to withstand the 480 volts. Can anyone with expertise in this area shed some light on this?
How was the drive energized as well? Find out more about the methods used to power up the drive.
When my maintenance team contacted me about a PowerFlex 70 drive that wouldn't turn on, I discovered a wiring error upon arrival. The incoming 480 volt was connected to the load side T terminals, while the motor leads were connected to the line side. Despite not having a spare drive, I noticed no damage and advised swapping the leads. Surprisingly, the drive worked perfectly once reconnected. I was amazed that the diodes in the drive remained undamaged. Could it be that the high reverse current of the diodes protected them from the 480 volts? In this case, the IGBTs isolated the load side, preventing the 480V from reaching it. The line side, connected to the motor, had no power. It's similar to a motor generating power back to the load terminals. The drive's operation was unexpected, as the internal control power bus is fed from the line side power source.
I witnessed an installation team mistakenly interconnecting the power supply side of a Variable Speed Drive (VSD) with the main power source and then linking the output side of the VSD to another VSD's input. Subsequently, they connected the output side of the second VSD to a motor. Fortunately, they recognized the error before powering up as they had an extra cable and noticed one motor lacking a connection. While the setup seemed puzzling, I've always pondered if it could have functioned by disabling load detection parameters in the initial drive and configuring it to operate at 50Hz with no acceleration. However, I refrained from experimenting with two 250kW drives.
It is not advisable to attempt the same process with PF525's, PF753, or PF755 drives as they may release the "magic smoke." While connecting old Reliance drives may result in powering up, an Over Current fault is likely when attempting to run them. I have also observed instances where PF700H drives have been connected incorrectly and only function properly when connected the right way.
In a forum post, user alan_505 discussed the potential risks of manipulating PF525, PF753, and PF755 drives, suggesting that doing so may release the "magic smoke" from the equipment. They explained how connecting old Reliance drives could result in an Over Current fault, while noting a scenario where a PF700H drive operated incorrectly until properly configured. The user shared a humorous yet frustrating anecdote involving a 10-hour support call to troubleshoot a PF527 remotely. Despite thorough troubleshooting, the issue was traced back to the incoming power being on the wrong side, leading to immediate overload upon activation. This experience highlighted the importance of correctly identifying motor connections. While the drive did not sustain damage, it refused to operate under the incorrect setup. It serves as a cautionary tale as some VFD models may fail upon incorrect powerup configurations.
It's indeed surprising the drive's diodes withstood this ordeal! However, diodes are designed to allow current in one direction and block it from the other, thus they can typically handle a fairly high reverse voltage. The nifty thing about the PowerFlex 70's design is that it employs robust fail-safes to prevent significant damage. Even still, the fact that the diodes didn't sustain damage under incorrect 480V connection is impressive and a testament to its solid build and design. Do keep in mind though, repeated incidents can wear out components over time!
Your PowerFlex 70's survival is indeed quite fortunate! Diodes typically wouldn't handle a reverse voltage that high without failing. However, it's also important to note that the duration of the reverse voltage application matters - perhaps it wasn't applied for long enough to cause damage. Alternatively, some heavy-duty components, like those in industrial drives, may have generous safety margins built in, which is why your drive could have weathered the mishap. Still, I wouldn’t count on this happening again in the future. Better to save the drive from stress whenever possible!
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Answer: - Despite mistakenly connecting the incoming 480 volts to the wrong terminals, no visible damage was observed on the drive. Swapping the leads allowed for successful power-on without issues, indicating that the diodes remained undamaged.
Answer: - Based on the experience shared in the discussion thread, it seems that the reverse current diodes in the PowerFlex 70 Drive were robust enough to withstand the 480 volts without being damaged.
Answer: - In the scenario described, simply swapping the leads helped in successfully powering on the drive without any visible damage. However, it is important to exercise caution and double-check connections to prevent potential damage in similar situations.
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