The first thing you should know when purchasing a VFD is to keep it clean, cool, and dry. If you follow these three recommendations, the life of your VFD will be greatly extended. Unfortunately, there will come a time when your VFD will encounter a problem (hopefully many years down the road). This article will cover some of the most common causes of VFD faults and failures and provide some tips and tricks to prevent them to keep your equipment in tip-top shape.

Poor Environment

VFDs are built like computers, and computers are extremely susceptible to dust, debris, moisture, and overheating. If you are using a VFD in an area that is consistently taking in dust, debris, or moisture the operating life of your VFD will be shortened.

In environments with high humidity, such as wastewater treatment plants, your VFD is at risk for circuit board corrosion from moisture being sucked into the cabinet through the cooling vents constantly. This, compounded by possible infrequent use, can enable moisture to build up without time for heat and ventilation to dry it out. To avoid issues caused by humidity, ensure that the operating environment and storage space for your VFD is clean and dry, and consider a dehumidifier to dry out the air (ensure the dehumidifier does not leak near any electronic equipment). For extreme humidity or wash-down environments a NEMA 4, 4X or 5 enclosures may be necessary.

Another common cause of VFD failure due to environment is the clogging of cooling vents by airborne particles, especially when combined with moisture or oil. Metallic particles can also short circuit your VFD circuit boards. Tracking or arcing marks across components or circuit board traces indicate evidence of contamination failure.

To combat negative side effects or possible catastrophic failure due to build up, clean all parts of your VFD at least monthly. Also make sure you are using the correct cabinet for your environment. Some cabinets have side vents for cooling airflow, but these are more open to contamination. You are able to purchase drives in a sealed, dust-free housing if needed. Remember: Keep your VFDs free from dust, debris, and moisture at all times.

Loose Connections

If you feel like your VFD is not performing quite like it used to, loose connections or aging components could be the culprit. High levels of vibration and heat production are the two main causes of loose connections and premature aging of certain components. This can lead to dangerous electrical arcing within the circuitry. Arcing can cause issues with other parts of your equipment and create a dangerous working environment for your employees or technicians. Loose connections can cause permanent damage to your equipment if not addressed as soon as possible.

Excess heat, usually caused by contamination buildup, can also occur when current exceeds the drives rated level or by loose connections. Checking the connections visually may not be enough to diagnose a loose connection; you may need to use a temperature probe or handheld digital pyrometer. Connections should never be hotter than the connecting wires; this is a sign of a loose connection. Overheating can cause blown capacitors, shorting, and excess wear on many different components.  

Wrong Equipment

Unfortunately, you may be recommended the wrong VFD for your equipment. If you accidentally connect your VFD to an incompatible motor or machine, performance degradation is inevitable. Always make sure you double or triple check the compatibility of your motors/machines before you connect your VFD to the device.

Overuse

Using VFDs beyond their manufacturer’s recommended operating limits (by choice or on accident) can contribute to failure. Using any component at a rating higher than its operating limit decreases the lifespan of said component and eventually leads to failure. To avoid issues due to overuse check that all inverters are being run within manufacturer’s recommendations.

High Bus Fault

This is a common fault that is caused by external factors. An instantaneous voltage spike in the ac line or an “overhauling load” created by the inertia of the machine is usually the cause a high bus fault. This happens when the load continues to rotate faster than the motor’s commanded speed. Usually when this happens, the VFD protects itself by tripping on a high bus fault and shutting off the IGBTs.

If your VFD indicates a high bus fault, ensure that the power supply is consistent and that the deceleration time is adjusted to match the load. If the process requires rapid deceleration, dynamic braking or a regenerative power control circuit may be added to assist the VFD and prevent a high bus fault.

Overcurrent Fault

This is another common fault usually caused by too-fast acceleration at start-up. To ensure you don’t have an overcurrent fault, check all power connections to ensure that they are properly attached. Loose power connections cause overvoltage or overcurrent, blown fuses, and inevitably VFD damage. Loose wiring can cause erratic drive performance. This can result in unpredictable speed fluctuations and an inability to control your VFD.

To help prevent overcurrent fault use an auto tuning feature (if your VFD offers it). This function enables the drive to identify the attached motor. This allows rotor information to be used in processor algorithms for more accurate control.

The second way to prevent overcurrent fault is to check the mechanical load for worn or broken parts, or excessive friction. Repair or replace any worn or broken components as needed.

The last way is to check incoming voltage and acceleration rate. If incoming voltage is too low, or the acceleration rate is set too fast, overcurrent fault is possible. Stabilize the incoming voltage and acceleration rate to correct the fault.

High Starting-Load Current

A high current or high load reading could possibly indicate mechanical binding or some unexplained changes in process speed or load. The power requirements for pumps and fans ran even just a few revolutions per minute faster than normal can overload a VFD.

Make it a point to inspect all components driven by the VFD before starting them up. Conveyors must be unloaded before startup, pumps should be cleared of all debris or ice, and moisture should be avoided on any load. Wet material is much heavier than dry material and can place an unexpected load on the VFD, this can cause motor or VFD overload.

Another way to reduce a high starting load is to use a VFD with an extended acceleration rate. This starts a load slowly and smoothly instead of jerking to a start. A slow, smooth start is easier on mechanical components and has lower line requirements because a VFD draws only 100-150% of the load.

Capacitor Fault

Electro-mechanical wear happens to electrolytic capacitors since they have a limited lifespan and age faster than other components. This in itself could be a cause of inverter failure.

Capacitors are also extremely temperature sensitive. Operating temperatures over the manufacturer’s recommendations (often caused by high current) will reduce the life of the components. Electrolytes evaporate faster at higher temperatures. Capacitor life increases when they are consistently used at lower than operating temperature.

Useful Questions to Ask for Diagnosis

When helping your VFD technician to troubleshoot your VFD, you should be prepared with the answers to these questions:

• What was the machine driving at the time of failure?
• Did the machine jam for any reason?
• Did any other devices trip at the same time as the VFD?
• Are there any power factor correction capacitors on site? If so, when are they switched?
• What was happening on the utility side?
• Did the utility observe any disturbances?
• Was there an electrical shutdown caused by lightning or brown outs?
• Was there any construction or welding going on near the VFD?

Talk to a VFD Technician

When you invest in VFDs to help with your application’s energy consumption, you are expecting your equipment to last a long time. When faults start occurring, it can get extremely frustrating to try and deal with on your own. Calling an experienced VFD technician is your best bet to ensure the repairs are completed in a timely and proper manner.

Got Questions About Servicing or Installing a VFD? We Can Help!

Call 800-595-5315 Or Connect With Our Expert Technicians Here:

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Daniel Kennedy

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Daniel is an experienced VFD tech who has over 10 years of VFD installation and servicing experience. He thinks he is funny and helpful, luckily most of us agree as well.

Variable Frequency Drives have quickly become one of the most effective ways to conserve energy in many motor driven applications. They have a high upfront cost, but can save you a lot of money in the long run if they are well maintained. This article will address some of the most important things you can do to extend the life of your drive.

Keep it Clean

Keeping an expensive item clean and protected from the elements should be a no-brainer. All VFDs should be kept in a cabinet to ensure a long life. We expect a VFD to last 3-5 years if it is mounted in the open with no shelter from dust and debris. If that same VFD was housed in a NEMA 1 or NEMA 12 rated enclosure, we would expect that VFD to last about 20 years, given it is well maintained and looked after.

Every time you perform maintenance, or even just open the cabinet to look at your VFD, you should be cleaning out any visible dust and debris. For the cabinet and heat sinks, you can use compressed air to blow the dust and debris away. For the more sensitive equipment, you should be using a vacuum, or a microfiber cloth to avoid building up static electricity. If any oil is visible on those sensitive parts you can usually use rubbing alcohol on a microfiber cloth to remove it. Be sure to check your specific manufacturer’s recommendations to see if this is an approved cleaning solvent. 

Keep it Cool

Overheating is one of the main reasons a VFD will fail, but it is often easily avoidable. Make sure that along with cleaning out the cabinet of any visible dust or debris, you also pay special attention to the fans and heat sinks. Debris accumulation in these areas can quickly cause overheating issues for your VFD.

Keep the ambient temperature at manufacturer recommended standards to ensure that your fans are not overexerting themselves in order to keep your VFD cool. Overexertion can lead to fan failure that if left unaddressed for even a short period of time, can lead to overheating of your VFD.

Keep it Dry

Another very important aspect of VFD care is to keep it extremely dry. Your VFD is essentially a very expensive computer that controls other very expensive equipment. And just like you wouldn’t want to let your laptop sit out in the rain, you don’t want your VFD to sit in any moisture for any period of time. Moisture is the number one enemy of electrical equipment. Moisture causes corrosion and short circuiting of the most delicate parts of your VFD. Usually, if moisture has found its way inside your VFD, you are too late to prevent failure.

If your VFD is in an area where you are worried about condensation, a NEMA 12 enclosure, close observation, and a space heater may be needed to combat moisture.

Preventive Maintenance

To keep your VFD in good working condition, inspecting the most critical elements regularly is key. With routine maintenance performed by a well-trained and knowledgeable technician, you should be able to remedy small issues before they become critical and cause unscheduled down time.

Ensure Connections are Tight

During maintenance your technician should be checking all connections for any looseness. Loose connections can cause hot spots in your cabinet, which can lead to electrical arcing. To ensure connections are tight, they can use an infrared camera while the drive is running to see if there are any visible hot spots. However, this method is not foolproof.  Another way to check for loose connections is to tug on each connection with your hands to see if they feel any give. If they do, they will tighten the connection to the manufacturer recommended specifications. Over-tightening your connections can lead to compromised screws, which can lead to loose connections down the road.

Got More VFD Questions? We Can Help!

Call 800-595-5315 Or Connect With Our Expert Technicians Here:

Other Articles

• 
  What is Right for Your System – Deraggers or VFDs?September 1, 2023
• 
  Convention Center Saves 8% in Energy UsageApril 6, 2023
• 
  Local University Uses EMC VFDs to Keep Facilities RunningMarch 9, 2023

Daniel Kennedy

VFD Technician

Daniel is an experienced VFD tech who has over 10 years of VFD installation and servicing experience. He thinks he is funny and helpful, luckily most of us agree as well.