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Replace bus caps Siemens Robicon medium voltage VFD

It is well documented that VFD bus caps have a limited life, and at some point need to be replaced. (See Capacitors: The Ticking Time Bomb) That’s especially true for high horsepower medium voltage VFDs such as the Robicon Perfect Harmony medium voltage VFD.

replacing medium voltage bus capsPart of the regular preventive maintenance we often perform on Siemens Robicon Perfect Harmony medium voltage VFDs includes inspecting, and after a certain age, replacing the bus caps within the power cells. The Robicon Perfect Harmony VFD is very reliable, and has been an industry workhorse for many years; however the capacitors do fail. (See: Robicon Capacitor Failures)

EMA recently performed this service at a large waste water treatment station in Georgia. While replacing the capacitors in a Robicon Perfect Harmony VFD isn’t especially difficult, it is time consuming and must be done with care.

The results of doing it wrong can be catastrophic. One of the cardinal rules of preventive maintenance service, whether on the Robicon Perfect Harmony medium voltage VFD or anything else.. is DO NO HARM!

There are also safety concerns, as there are with any medium voltage VFD service.

Robicon Perfect Harmony Bus CapacitorSince the bus caps used in most medium voltage VFDs, including the Robicon Perfect Harmony VFD, use screw terminals to make the mechanical and electrical connections, one must exercise great caution in getting the connection snug enough, but not stripped. Either loose or stripped connections will almost always result in arcing and heating, leading to a cell failure. Technicians must never submit to the common temptation to use improperly sized screws for this very reason.

In short, the capacitor replacement job in a Robicon Perfect Harmony medium voltage drive requires a methodical and careful approach.

EMA Toshiba Medium Voltage VFDPreventive Maintenance on medium voltage VFDs involves much more than simply replacing bus capacitors. Very often, over time, the tuning can be off, and electro-mechanical devices such as interlocks, auxiliary contacts, and other mechanical linkages can have issues, which will at some point cause either a complete failure or unexpected downtime.

Medium voltage VFDs are expensive, and usually critical to the plant operation, so downtime is harmful. Failing to perform proper maintenance on Robicon Medium Voltage Perfect Harmony VFDs, as with all brands of medium voltage VFDs, can result in catastrophic damage, and since critical parts can have long lead times, should be avoided if at all possible.

Just for your information.. EMA stocks the power cells for the Robicon Perfect Harmony VFD (see Robicon Power Cells in Stock) .

If you need either repair service OR want to talk with us about preventive maintenance on your Robicon Perfect Harmony VFDs, or any other brand of VFD, call us at 800-8848-2504 OR hit any of the contact methods on the right of this page, including live chat.

No One, Anywhere, is Better at Drives than we are.. no brag.. just fact.. try us!


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