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Instantaneous Over-Current Mystery Solved By Remote Monitoring Tool

Medium Voltage Variable Frequency Drives such as the Toshiba T300MVi are typically reliable and user-friendly, but like all electronics, they do experience failure. Heck, we make a living fixing VFD failures! A customer recently experienced a failure that baffled them, and it presented an interesting opportunity for us to utilize one of the best troubleshooting tools we’ve ever found for medium voltage variable frequency drives.

The Problem

The drive was failing on “OCA” fault immediately upon drive startup. Sometimes, they could get it to reset and run but other times, they had to switch the fan it was running to an across-the-line bypass. 

Toshiba T300MVi failing OCA message

EMA Troubleshooting:

During an outage, we installed a DriveScan remote monitoring tool hoping to get better insight into what was going on within the medium voltage VFD itself; thankfully, it was instantly able to prove its worth. The DriveScan captured 3-phase current draw during the next startup and subsequent OCA failure. By observing the trended output current data captured by DriveScan, we were able to see the V phase current draw was significantly less than the U and W phases, indicating a problem within the V phase power cell. The drive was started 4 times and it failed every time.

Toshiba T300MVi current draw and OCA failure

The Verification:

To future test our theory that the motor/load itself wasn’t the issue, we observed output current draw when the motor was across the line and all was balanced, proving that the motor/load was fine.

testing a power cell of a Toshiba T300MVi

During the next outage, they swapped the suspect cell from the V phase to the W phase to further test our theory. The symptoms moved to the W phase, verifying our theory that there was, in fact, a problem on the suspect Toshiba power cell. 

cell replaced and issue resolved

After removing the bad power cell and replacing it with a spare, the drive started up and ran with no problem. It has been running ever since.

after bad power cell replaced

The Solution:

By utilizing DriveScan, the problem cell was easily identifiable from the comfort of an office without taking dangerous “hot” readings or paying for expensive field service calls. DriveScan is not limited to the T300MVi or even Toshiba drives. DriveScan is installed all over the world on multiple medium voltage VFD manufacturers and brands.

remotely monitor medium voltage variable frequency drives

DriveScan’s unique, independent sensors monitor all aspects of VFD health and give users unparalleled insight into internal and external factors affecting drive-related issues.

In this particular instance, DriveScan saved the customer thousands of dollars of troubleshooting downtime and prevented an eventual catastrophic failure because of the bad power module. Do you have a problem with your medium voltage variable frequency drive? EMA offers a variety of solutions including the DriveScan remote monitoring tool.

Call us at (770) 448-4644, Email Us ,or Chat with us to schedule a personal demonstration of DriveScan in order to see if it is a right solution for you!


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