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Service on an Oil Pipeline Robicon Perfect Harmony VFD

EMA does a fair amount of service for pipeline companies, and in particular on their medium voltage VFDs. This particular call was in Houston, Texas on a Robicon Perfect Harmony 4160 volt medium voltage variable frequency drive.

This particular Perfect Harmony Robicon VFD was faulting out on “IGBT Device Out of Saturation Fault”. Upon arrival I checked all the power components on the Robicon VFD and found no shorts.

NOTE: IF you need service, call 800-848-2504 now, or hit the contact Icon on the top right of this page OR the “Live Support” icon.

I disconnected the motor, powered up the drive, and ran a cell diagnostic test, which all the cells passed. I then ran the medium voltage drive without the motor; it ran for few seconds and faulted on “Overspeed”. This is normal for a drive that is operated without a motor attached. This can alleviated, if necessary, by tuning the speed PID gains, but in this case, I saw no reason to do so.

I then powered down the MV VFD. After waiting for the bus capacitors to discharge, I measured the resistance between the phases and ground. I found the motor phase to ground reading 18 ohms, indicating a shorted motor to ground. The customer also had a megger at the job site, so we megged the motor and it would not go beyond 0.3 V with readings of 10K Ohms to ground. We concluded the motor was bad.

While finding a bad motor isn’t especially uncommon, given the size of this motor, and most medium voltage VFD applications, one needs to be certain that the motor is in fact- failed. Removing and replacing a 2500 Horsepower 4160 volt motor is difficult mechanically, and replacements are not always readily available. Since oil pipeline VFD applications are normally critical, it’s important not to make a false diagnosis.

While at the job site I looked at the bus capacitors which I noticed had their venting holes plugs raised. (See Electrolytic Bus Capacitors: The Ticking Time Bomb )

Bus Capacitors older than 10 years should be carefully examined. There are 432 bus capacitors on a 2500HP 4160V Robicon Perfect Harmony MV VFD. Beyond the 10 year mark, the chances of catastrophic damage increases exponentially. EMA routinely offers PMs on the Perfect harmony that includes replacing electrolytic buss capacitors. (See Medium Voltage VFD Preventive Maintenance)

See the bottom of this page for your nearest EMA location, OR hit the contact Icon at the top right of this page. We can quote preventive maintenance to your Oil Pipeline Medium Voltage VFDs of all brands. We routinely repair and service The Allen Bradley Powerflex7000, WEG MV01, Mototronics MVSS and Toshiba T300MVi.


One Response

  1. A basic static check of the output will give you an idea of the condition of the IGBTs.
    To access them on that drive you unfortunately have to strip it down to the heatsink where they are mounted.

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