If You Take Care of Your VFDs, They Take Care of You
Quick quiz: name an electrical component that effectively controls several electric motors in such a way that within a year it pays for itself. What is it?
Of course, it’s an easy answer with the article title looming above this text. Variable frequency drives (VFDs) provide solutions and energy savings. Yet there are many people who are either afraid to make the financial commitment — a downside of a VFD is they are expensive — or they don’t know how effective drives are and how they help your bottom line.
To give you a good picture of VFDs, we’re going to explore some common VFD benefits give you. Like any piece of equipment, if you want it to serve its purpose and have a long working life, you need to maintain it. We’ll also talk about some common maintenance tasks for your VFD. If you take care of your VFD, it takes care of you.
Overview of VFD Provides
Besides controlling the voltage and frequency applied to a motor, VFDs provide extra benefits. Here are a few for your consideration:
Efficiency
One of the many benefits of using a VFD is its ability to save energy. Because the VFD adjusts the motor’s speed about how much is necessary, you’re only using the least amount of energy for any given task.
The amount of energy saved using a VFD is quite considerable. In fact, over a relatively short amount of time, the drive pays itself back from energy saved.
Regenerative Energy
In simple terms, an electric motor is an energy conversion device. A motor converts energy to mechanical torque when applying electrical energy.
In some instances, an electric motor does the reverse, depending upon the connected load’s nature. When reversed, mechanical torque converts to electrical energy called regeneration.
The main benefit of regeneration is when the amount of recovered energy is significant compared to the more expensive regenerative VFD. These applications include systems that start and stop quite often, such as:
- Conveyor belt drives
- Lifts and hoists
- Automated storage and retrieval systems
- Tension unwinders
- Centrifuges
Functionality
Many drives are capable of detecting a range of variables, including temperature, movement, and pressure. As a result of those variables, the drive determines the frequency and adjusts motor speed to match the needs.
Start Currents
Depending on the type of VFD used, there is a reduction in start currents of up to 80%, even though the torque is not affected. The resulting starting current reduction reduces the possibility of equipment failure. The current reduction also leaves the local grid alone, so it affects nothing else in the area.
Reliability
Some of the newer VFDs offer options for protecting against short-circuiting. These more modern drives prevent unexpected motor rotation during an emergency by stopping the torque power from reaching the drive.
Longer Equipment Life
By optimizing the performance of the equipment that it is operating, the VFD limits wear and tear and reduce the possibility of mechanical failure. Making those necessary adjustments places less direct stress on those electrical components in the system.
Incentive (Rebate) Programs
A new VFD may be eligible for incentives. There are conditions your drive and application need to meet. For example, Focus on Energy summarizes the criteria involved:
Focus on Energy offers financial incentives for the installation of energy-efficient variable frequency drives (VFDs) in existing buildings. Incorporating energy-efficient VFDs into your facility is a great way to reduce costs and boost your bottom line. By keeping motors from running at 100 percent capacity constantly, or cycling fully on or off, virtually any application that uses motors to drive fans and pumps can find significant savings. The types of environments that often benefit from VFDs include:
- Industrial Manufacturing
- Universities
- Hospitals
- Office Buildings
- Facilities
- Food-Processing Plants
Summing up VFD Benefits
These are a few of the many benefits available when using a VFD. When they are set up and maintained, you even see an ROI in well under a year. These benefits and more are possible, thanks to what the VFD has to offer.
Key Maintenance Points for Your VFDs
Since we tend to get so much from VFDs, it is important to consider what they need to perform as well. When you take care of your VFD, it continues to take care of you for many years to come.
VFDs Preventative Maintenance
VFD Preventative maintenance is always a good idea. From time to time, however, give particular attention to the VFDs in your facility. The care your VFDs receive is especially crucial during a scheduled plant shutdown. Shutdowns occur during slower manufacturing months or they or over the holidays.
Regardless, shutdowns provide a prime opportunity to take care of your drives. When your plant shutdown is over, the attention you gave your drives ensure they are ready for action.
Watch out for Moisture
One resulting issue for drive failure is condensation buildup. Condensation is a problem during a scheduled shutdown if there are temperature variations. Condensation destroys the VFD and the electrical components. Make sure that you use heaters in the area of the drives your working on to reduce the possibility of condensation.
The side vents for most VFDs place them into NEMA 1 or NEMA 12 categories. Obviously designed for airflow, these vents fall prey to dust contamination. That contamination reduces airflow, which in turn reduces the performance of the drive.
Keep Things Dust-Free
Not only is a dusty house the enemy of your grandmother, but dust is also dangerous to a VFD. A dust buildup causes problems by itself or when it absorbs any moisture.
Spraying compressed air to clean inside the VFD works in some environments. However, the air in a typical facility contains water and oil. Pay attention and know your environment; using compressed air in a damp plant environment sometimes isn’t the best choice to use for your drives.
Even if you sprayed dry, oil-free air into your drive isn’t the solution is other environments. Even though that specialized air supply is expensive, it creates a risk of generating static charges within the drive components.
Check the Fans
Overheating is too important an issue to ignore when it comes to the health of your VFDs. Too much heat is one of the more serious problems associated with VFD failure. But, overheating is something that is often avoidable.
When maintaining the VFD, check the fan to ensure that it is not obstructed and there is no build-up of dust or dirt. Cleaning the fans on a regular basis reduces this possibility.
Do Some Tightening
Although this is a logical and obvious step to consider, missing loose connections opens the door to many problems within the VFD.
How do these connections find themselves loose? Primarily from continuous mechanical vibration, heat cycles, and standard maintenance practices are the leading culprits.
If a connection is bad, look for arcing. If arcing occurs at the VFD input, look for three problems:
- Resulting nuisance over-voltage faults
- Input fuse clearing
- Damage to protective components
The VFD output isn’t safe from arcing either. Arcing results in overcurrent faults or damage to the power components.
Arcing inside the VFD isn’t the only thing to be concerned about. If any control wiring connections are loose, keep an eye out for erratic drive operation.
Missing loose connections is part of the problem. Human error plays a role, too. Tightening screws too much or too often ruins connections.
Preventive Maintenance for VFDs: What Else to Consider
Here are six more things to add to an effective VFD preventive maintenance program:
- Do not forget to look at the internal VFD components as a part of a normal, mechanical inspection plan.
- Keep an eye on circulating fans for any symptoms of foreign objects or bearing failure.
- If you have spare VFDs, make sure the space you store them is a dry, clean environment without condensation.
- If you’re storing spare VFDs for extended periods of time, turn them on for a little while every six months. This schedule keeps the DC bus capacitors healthy.
- Maintain a regular schedule to keep an eye on heat sink temperatures
- Look for bulging and leakage while examining DC bus capacitors. These problems are symptoms of component stress or electrical misuse.
Don’t Rush Your VFD Back
When you are dealing with an extended shutdown, it may take some time for the VFD to be ready to get back to work again. Play it safe!
Rather than starting the VFD like usual, ramp it up in stages. For example, increase the voltage by 20% steps over an extended time until reaching the full link voltages. Keep a close eye on the leakage current voltage drop across the resistor. Shut things down if there is a sudden increase in leakage current.
For additional safety, do not stand in front of the capacitors when starting up the VFD. There is danger from exploding capacitors.
In Sum
Choose an effective preventive maintenance program for your VFDs that works best for you. Following this program keeps the drive working its best while keeping repair costs low.
Repeating what I wrote before; if you take care of your drive, your drive takes care of you. VFDs are such a valuable tool in your toolbox.
Don’t just take one out of the toolbox and wire it to a motor and expect it to work. Contact a reputable company with years of VFD experience. They’ll take a look at your situation and determine specifications unique to your situation and provide solutions for you to consider.
