By Mike Orlik
MER has been selling, installing, and commissioning more Variable Frequency Drives (VFDs) for the past few years. While VFDs are a great choice to reduce in-rush amperage on higher horsepower motors and help increase the lifespan of your electric motor, there are a few key items you need to consider first.
1) Identify the location you have selected that will work for the VFD. Check the installation manual for any restrictions, such as temperature and mounting orientation.
2) Make sure you have an electric motor suitable for VFD use. If you do not have an electric motor that is suitable for VFDs, there is a good chance it will still work with one, but it would not have the same level of protection against voltage spikes or overheating. To get the most use out of your VFD and electric motor, you would want an Inverter Duty Motor. Almost every major electric motor manufacturer makes one.
3) Selecting the correct cable is also important. Your standard marine grade, low smoke cable may work and get the electric motor to turn over, but there will be complications. VFDs put out electromagnetic interference (EMI), and if you use the wrong type of cable, you will see an increase in EMI. Other factors that play a hand in EMI are cable length, load type, VFD design, and switching frequency. During the installation phase of a VFD, I have been using an XLPE (Cross-Linked Polyethylene) shielded cable. The shielding reduces EMI, has good thermal properties, is low smoke, and is somewhat flexible, making installation smoother and cleaner. If you are using external output functions, also use a shielded control cable.
4) Grounding your VFD is very important and is one of the most common issues I have encountered. Improper grounding could lead to ground faults on your vessel, your VFD not working correctly, and, most importantly, improper grounding could be fatal. Every VFD manufacturer is different in how and where you should ground. In common installations, you strip a piece of jacket in the cable and clamp it inside the VFD cabinet. The same applies to shielded control cables. You also install a place for your ship’s ground cable inside the cabinet. Again, every manufacturer is a little different so make sure you read the installation guide to make sure you ground everything in the system correctly.
Following these four steps during the installation phase eliminates the risk of having issues during start-up and creating more downtime. The last step is programming the VFD. Most manufacturers have quick start videos that will get you programmed and running in about 20 minutes. Once you have completed all the steps listed above, you will be ready to use and enjoy the benefits of your VFD.