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Things To Check When You PM Your Medium Voltage VFDs

There are several words that can be used to describe maintenance: “preventative”, “preventive”, “predictive”, etc. Whatever term you decide to use, maintaining your medium voltage VFDs is an absolute must if you plan on having long life out of your investment. Performing preventative maintenance on complex equipment such as VFDs can be a bit daunting, BUT a few simple checks can go a long way.

Medium Voltage Drive Preventative Maintenance Checklist

1. Loose Connections: Loose connections are a major cause of VFD failure and something that is easily addressed. Power connections that are loose will arc, causing oxide to build up, and eventually break the connection or create so much heat that the wires burn. Control connections, although they draw very little current, need to be checked as well. A loose control wire will cause your drive to do all sorts of things you don’t want it to do and leave you scratching your head for hours.

2. Dust, Dirt, and Debris: VFDs are often in extremely rugged and harsh environments where dirt and other contaminants can easily get inside of your medium voltage drives. Contaminants can cause a variety of problems, particularly heat dissipation. The switching components within the drive: diodes, SCRs, IGBTs, etc., produce heat and without a proper way to dissipate that heat, they run the risk of failure. The “10-degree rule” essentially says that every rise of 10 degrees Celsius reduces the life of electronic components by half. Although, this can’t be exactly calculated, it does serve to remind us that heat kills electronics. A good preventative maintenance program should address dust, dirt, and debris within VFDs to make sure they’re dissipating their heat as efficiently as possible.

dust dirt and debris can cause drive failures

3. Predictive Maintenance Readings: The “P” in PM is often for “preventative” but the word “predictive” can apply as well. By taking simple measurements such as input/output voltage and current, capacitor ripple, and low voltage power supply tolerance, one can reasonably predict problems BEFORE they become an issue. Taking live measurements, preferably when the drive is operating within normal conditions will give you a good indication that there is something that needs to be addressed. Readings such as high capacitor ripple is a major indication that the capacitors within your drive are failing and imbalanced output current can indicate power cell or motor/load problems.

Unfortunately, taking readings on medium voltage drives is tedious and often unsafe, so utilizing remote monitoring tools can prove very helpful for this critical task. The DriveScan remote monitoring tool continuously monitors all aspects of the VFD 24/7/365 and the readings are trended, allowing users to easily access the information at any time. DriveScan is the perfect compliment to a comprehensive PM program. For more information on DriveScan, please contact us.

4. Proper Programming: A bonus benefit of preventative maintenance is that it gives you the time to evaluate if the drive is operating as it should. I cannot tell you how many times I’ve PM’d a drive only to find that several parameters could be changed to make the drive operate better. In a production environment, the mantra is often “if it runs, keep it running”, but a PM is a great time to go through the drive’s settings and make sure it is actually set up to run as effective as it could. Warning: BEFORE you change any parameters, it is best practice to save them all first via the manufacturer’s software. Whenever parameters are manipulated, you run the risk of making things worse than better, you always want to be able to at least get back to where you started.

5. Visual Indications: Perhaps the best troubleshooting tool we have is our eyes. A good PM program should involve visually inspecting the entire medium voltage drive for signs of failure. Many problems or potential problems can be found by someone with a trained eye. However, for a visual inspection to be effective, the person performing it does need to be intimately familiar with VFDs, their components, and their function. I can ask my 8-year-old son to look inside a VFD, but because he doesn’t know what a normal condition should look like, he can’t tell me what an abnormal condition looks like either.

Get the Help you Need with Your Medium Voltage Drives

If all this is overwhelming to you? Let us help! At EMA, we perform predictive and preventative maintenance on medium voltage variable frequency drives on a daily basis. If your organization lacks the time or expertise to properly perform a PM, EMA can meet that need for you. Contact us today for more information or a quote.


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