The role of maintenance and safety for VFDs and VSDs in manufacturing facilities

Keeping variable frequency drives (VFDs) and variable speed drives (VSDs) running safely and efficiently is more important than ever as companies try to keep downtime and worker incidents to a minimum

Respondents:

• Richard Barrows, senior electrical engineer, Hitachi Global Air Power, Michigan City, Indiana
• Zack Fowler, product marketing manager, Atlas Copco, Rock Hill, South Carolina
• Eder Matias, director of sales, drives, controls & automation, SEW-EURODRIVE USA, Lyman, South Carolina
• Craig Nelson, senior product manager, Siemens Digital Industries, Alpharetta, Georgia
• Paulo Guedes Pinto, chief technology officer, Infinitum, Round Rock, Texas
• Brandon Teachman, owner, Automation Coffee Break, Appleton, Wisconsin

Question: Are there specific maintenance practices and preventive measures that can extend the lifespan of variable frequency drives (VFDs) and enhance their reliability in demanding operating environments?

Zack Fowler: There are several maintenance practices and preventive measures that can significantly extend the lifespan of VFDs and enhance their reliability. Regular cleaning and keeping the unit tidy are essential to prevent dust and debris buildup, which can cause overheating and component failure. The use of filters can help in maintaining clean airflow and protecting internal components from contaminants.

Eder Matias: Always read the manufacturer instructions regarding preventive maintenance measures. At a minimum, panel mounted drives can have extended life by using a temperature-controlled panel and keeping the electrical cabinet free of dust, humidity and industrial debris. Line chokes and line filters are optional components which can extend the inverter lifespan by isolating the devices from power surges. Motor-mounted inverters is a tested and proven product which withstands harsh conditions due its high overload capabilities and high ingress protection rating (IP65).

Craig Nelson: What is proven for other electrical equipment is also true for drives. Operate them in a cool, clean and dry environment and do not power cycle them excessively.  Regular maintenance such as fans or filters will also pay dividends on the VFD life.

Brandon Teachman: Some key maintenance practices to extend VFD lifespan and ensure reliable operation:

• Cleanliness is king: Dust and debris act as insulation, trapping heat within the VFD. Regularly schedule cleanings using dry, compressed air to remove dust buildup.
• Conquer the heat: Heat is the enemy of VFDs. Ensure proper ventilation around the drive to allow for adequate heat dissipation.
• Power quality: Voltage fluctuations and spikes can wreak havoc on VFDs. Invest in power correction to maintain consistent and clean power to the drive.
• Embrace inspection: Regularly inspect the VFD for loose connections. Tighten loose connections.

Question: VFDs can cause bearing currents and shaft voltages in certain motor types. What are the best practices to prevent or minimize these issues and ensure the longevity of motors?

Richard Barrows: Adding grounding brushes to the motors can dissipate any induced currents. You can also use isolated and non-drive end-bearing caps. There also are certain types of cabling that can help reduce currents.

Zack Fowler: To provide proper earthing and if needed, we can use insulated bearings.

Eder Matias: There are several reasons that could potentially generate bearing and shaft currents, inverters being one of them. Proper motor and machine grounding, low pulse-width-modulation (PWM) frequency, shorter motor cables or a motor mounted VFD are some of the common practices to avoid these types of problems. The benefit of pairing gearmotors and inverters in the same application is that we can take several measurements from the VFD to the motor bearings and seals to mitigate this issue and increase the overall system availability.

Paulo Guedes Pinto: There are multiple ways of addressing bearing currents and shaft voltages. The most common is the use of a grounding ring or grounding brush. These devices provide a path for the current, avoid it running through the bearing and causing premature failure. Another approach is the use of hybrid ceramic bearings that prevents the bearing from being a path for the current. Finally, the use of a common mode choke on the VFD output reduces common mode voltage and reduces the bearing currents.

Question: How do you troubleshoot common problems with VFDs, such as overvoltage, undervoltage and overcurrent faults? What are the best practices for diagnosing and rectifying these issues?

Richard Barrows: Always check and monitor the incoming power to verify sufficient voltages and minimal phase imbalance. Regarding overcurrent, plant managers need to verify that the motor load has not changed, such as a change in process parameters or perhaps mechanical damage. The addition of power monitoring equipment upstream can identify power issues early. Finally, regular maintenance and monitoring of the motor and driver equipment is important to avoid load side issues.

Eder Matias: When troubleshooting any VFD and motor installation, it is most important to assess the situation and never start replacing random parts before you diagnose the issue. Never assume anything, and remember that rushing a diagnosis won’t necessarily solve the problem faster. The goal is to avoid making a small problem a big problem.

Take one step at a time, create a back-up of the VFD parameters and look at the fault history. Next, do a lockout/tagout (LOTO) and look for loose wires or connections. If the visual check is ok, use your meter and look for lower insulation or higher impedance depending on what you have seen in the fault history. In my experience, problems are often more basic than they might appear.

Craig Nelson: Most VFDs today offer extensive diagnostics built into the drive and are very fast in enacting a fault to protect themselves. Some drives even offer a matrix code on them for fast access to diagnostic material such as manuals or support sites. I also find internet searches provide a wealth of information when troubleshooting a VFD.

Question: In critical applications, such as those involving pumps or fans, what are the considerations for implementing redundancy and fault-tolerant configurations with VFDs?

Brandon Teachman: There are three key considerations:

1. Level of redundancy: Standby redundancy with automatic switchover may suffice for a simple pump. Critical processes might demand full redundancy, with both VFDs running in parallel, sharing the load, and being ready to take over instantly if one fails.

2. Look at the system: Don’t stop at just the VFD itself; consider redundant power supplies and control.

3. Testing: The best redundancy plan is useless if it does not work. Regularly simulate failures and practice switchover procedures.

Question: How can predictive maintenance be applied to VFDs to enhance reliability and reduce downtime?

Richard Barrows: One of most important things is to regulate heat. You do this by keeping them clean:  heat sinks can get dirty due to environmental issues. You have to clean them regularly to keep the drive running at a lower temperature.

Eder Matias: SEW-EURODRIVE takes the approach that monitoring components is as important as monitoring the complete application. Customers want to see the overall state of the machine rather than individual components. Our MOVI-C Automation Platform system offers a condition monitoring feature called DriveRadar. When SEW-EURODRIVE gearmotors and VFDs are paired in an application, DriveRadar is capable of using our inverter as a true application sensor without any additional components or any extra installation efforts. In the past, this was only possible by installing additional components which adds costs and complexity.

Craig Nelson: Basic preventive maintenance of all electronic equipment is imperative but built-in preventive functions like cooling fan runtime functions built into VFDs are now issuing warnings to prevent downtime. When a condition monitoring system is used with motors and drives the complete machine downtime is reduced.

Paulo Guedes Pinto: VFDs can provide operational information in real time including temperature of critical components. In addition, VFDs can provide fault information. By tracking these operational parameters and faults, the maintenance team can identify trends and decide if the VFD should be replaced or not before a serious fault occurs.

Question: What safety precautions should be taken when installing and operating VFDs?

Richard Barrows: Always follow standard best practices around electrical safety guidelines. Adhere to lock out/tag out policies; use arc flash protection, and always wear appropriate personal protective equipment (PPE).

Zack Fowler: Make sure to power them off and wait at least 15 minutes before working on them to allow capacitors to discharge.

Craig Nelson: The attributes of the connected power supply and suitable protective device such as a circuit braker are very important in installing a VFD. The power system must be strong enough to trip the protective device in case of a short circuit or other event but the drive and protective device must also be rated high enough for the connected power system in the SCCR rating. Minimum enclosure volume is another important requirement often overlooked.

Paulo Guedes Pinto: The safety protocols while installing a VFD are similar to safety protocols applicable to the installation of any other piece of equipment with the same voltage and power rating. As VFDs do have capacitors in their dc bus, in situations where the VFD housing must be opened, it is important to wait a few minutes before removing any covers to give time for the capacitors to discharge. Usually, VFD manufacturers will put a label on the VFD enclosure indicating how much time one should wait before opening the enclosure.

Question: How do environmental factors, such as temperature and humidity, affect the performance of VFDs?

Richard Barrows: Environmental factors can be critical in selection, sizing and installation of VFDs. Dusty or particle-laden environments can foul a VFD’s heatsink, and that impacts the drive’s ability to stay cool. This can result in output de-rating, over-temperature faults and, ultimately, shortened life. These temperature-related issues can also be the result of high ambient temperatures surrounding the drive, or even exposure to direct sunlight. As with all electronics, exposure to excessive moisture should be avoided. Drives suitable for direct water exposure can be chosen and suitably rated enclosures should be chosen.

Zack Fowler: Our VFD units are designed to operate optimally at temperatures up to 115 °F. As long as the ambient temperature remains below this threshold, the VFDs will deliver consistent performance as intended.

Craig Nelson: The VFD’s environmental protection rating or the enclosure rating it is installed in play an important consideration in the environment it will operate in. If the VFD is not properly protected from contamination or humidity premature failures of the electronic boards are a very good possibility. Vibration and high temperatures can also result in premature VFD failure.

Question: How often should the firmware of VFDs/VSDs be updated, and what should be considered when performing a firmware update?

Zack Fowler: The firmware of VFDs and VSDs should generally be updated only when necessary, such as to address specific issues, improve performance, or enhance security. If the machine is running fine, it is often best to avoid unnecessary updates to prevent potential disruptions.

Eder Matias: This shouldn’t happen very often. The manufacturer should advise on how often the VFD firmware needs to be updated and why. Common sense and experience recommend caution when performing firmware upgrades. After the upgrade, one might solve a known bug but create incompatibility problems, and, the application may not run at all after the upgrade. Always consult with your VFD supplier prior any firmware update.

Pablo Guedes Pinto: Whenever possible, the firmware of VFDs should be updated as soon as a new firmware version is released.

Question: With the advancement of semiconductor technology, what new trends and features are emerging in modern VFD designs?

Pablo Guedes Pinto: The electrification of vehicles has been enabled, among other things, by the availability of increasingly higher power silicon carbide (SiC) MOSFETs. This also has helped to reduce the cost of SiC devices and enabling their use in other applications. SiC devices can operate at higher switching frequencies without sacrificing efficiency. Another recent development is the availability of gallium nitride (GaN) MOSFETs which can operate at even higher switchihg frequencies than SiC. The use of high power GaN devices has been limited to low voltage applications (under 300 V).

Question: What are the key electrical parameters that should be measured during VFD and VSD maintenance and what mechanical checks are necessary?

Richard Barrows: Always check incoming voltage — look for current phase to phase voltage differences. From a mechanical viewpoint, It’s more about tightness of electrical connections and verifying appropriate torque. Finally, create and maintain appropriate protection and ventilation for the drives via an appropriate electrical cabinet, which protect the drive from dust, water another environmental factors.

Question: How big a role does cybersecurity play in VFD/VSD protection and how are engineers and technicians addressing the problem?

Craig Nelson: Cybersecurity or any form of unwanted manipulation of a VFD is becoming a big concern for VFD users. Network security and user management access control (UMAC) are now being incorporated into the VFD design to keep these critical devices operating safely. In the near future, these protective measures will become part of the various certifications required for VFD’s.

Brandon Teachman: I have not seen VFDs playing a role in cybersecurity plans as they are typically behind a firewall with no outside access. I have been seeing password protection being enabled on the drives to prevent people with local access from making changes. Some put in a managed switch per cabinet, allowing additional restrictions on these VFDs.