At EMA, we specialize in Medium Voltage VFDs, and the Siemens/Robicon Perfect Harmony drive is one of the most prevalent VFDs that we work on. In the higher horsepower ranges, many drive manufacturers, including Siemens, utilize a liquid-cooled structure for drive cooling as opposed to the more common, air-cooled method. The reason for this is often because of space constraints. The larger the drive, the more heat it generates, and air-cooling a large drive requires a massive enclosure coupled by massive fans. By using a liquid-cooled structure, the frame size of the drive can be drastically reduced.
The Advantage of Liquid Cooled Cells
On the Siemens/Robicon Perfect Harmony series liquid-cooled drives, the cooling lines physically run through each individual power cell as well as the transformer, which is a much more efficient way to cool the cells. The switching components (diodes and IGBTs) produce a significant amount of heat when running, so by running glycol lines directly through their heat sinks, the cell can operate effectively and efficiently.
The Trade Off
The disadvantage of this cooling method is the maintenance associated with it. Not only do you have to be a VFD expert to work on the drives, but you also have to have some plumbing expertise as well! These drives have a separate cooling system complete with pumps and heat exchangers which requires a completely different skillset to service.
Years ago, we had a customer whose capacitors on one of their liquid-cooled power cells blew out (as capacitors are known to do) and put a pin-sized hole in the glycol lines, causing glycol to spray all over the drive! We recently had a customer who’s liquid cooled transformer on their Robicon Perfect Harmony Series drive had a cooling issue and the transformer filled with glycol (see video).
The Experts
At EMA, we’re intimately familiar with repairing Siemens/Robicon liquid-cooled power cells; we do it all the time! Our in-house service engineers know all the steps necessary to fully repair, refurbish, and test liquid cooled power cells. We keep parts on the shelf to repair these cells which gives us a quicker turnaround time than you’ll find anywhere else.
Breaking down these cells is as mechanical as it is electrical. First, the top portion that has all of the switching components and the glycol lines has to be separated from the bottom section containing the capacitors and buss bars.
The bottom section buss work is removed to expose the capacitors and all of the capacitors are changed.
On the top side, all Diodes, IGBTs, balancing resistors, driver boards, and the cell control board are all tested and changed if necessary.
Once all the necessary repairs are made, the unit is initially tested with our portable Siemens/Robicon cell tester. If it passes all of those tests, the cell is then hooked up and run on our full load stand.
From the beginning to end, you can trust EMA with your Siemens/Robicon Liquid Cooled power cell repairs. Our experienced repair team will get your cell repaired in much less time than the manufacturer and each cell comes with a comprehensive 1-year warranty. Email us, call us, or chat with us to get your cell repaired today!