VFD commissioning

VFD System
Copyright C J Cowie at the English language Wikipedia CC BY-SA 3.0 https://upload.wikimedia.org/wikipedia/commons/e/e5/VFD_System.png

Coming fresh off a series of commissioning projects where there has been a commonality with the VFDs being furnished and commissioned by 3rd parties it dawned upon me there is a timeless note to share.  When commissioning a VFD always check the VFD speed reference input is properly configured.  Take the time to coordinate with the VFD technician, give a list of the signal types and interlock requirements from the PLC perspective.  Many, if not most, drives ship with 0-10 VDC signal reference as a default, and typically DIP switches and/or parameters within a drive need to be reconfigured when using a 4-20 mA signal reference.  If you don’t catch it before you attempt to start the drive in auto/remote you will see the VFD ramp immediately to full speed and there can be severe unintended consequences to the process.   I have seen this happen too many times, despite sharing with the VFD commissioning technician that our PLC’s speed signal is 4-20 mA.  DIP switches are often well hidden and setting them properly is easily missed. It may beg the question why so obstinately use 4-20 mA speed reference signals, but that sounds like a good topic for a follow up post.  Another great question is wouldn’t it be better if the controls integrator supplied and commissioned the VFDs?  Some drives are better suited to a particular application, so if you use an HVAC drive in a water treatment application you can almost guarantee there will be a mismatch in speed reference signals.  When RCK supplies drives we ensure the VFD matches the application thereby handling some of the easy to avoid mistakes by virtue of specifying and ordering the right product for the process.

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