DIG DEEPER – OCTOBER 2025
Maintaining Variable Frequency Drive Capacitors in Microtunneling
Written by Weston Alberts
Variable Frequency Drives (VFDs) play a critical role in microtunneling operations by allowing operators to control the speed of three-phase electric motors. This control is essential for managing the cutterhead and slurry flow rates under varying conditions.
Role of Capacitors in VFD Operation
Many VFDs use electrolytic capacitors to store electrical energy. Incoming alternating current (AC) is converted to direct current, which is then stored in these capacitors and supplied to the motor at the commanded frequency and voltage. This energy delivery enables precise motor speed control.
The Problem: Capacitor Degradation During Storage
Electrolytic capacitors have a known vulnerability: their dielectric (insulating) layer degrades over time, particularly when the capacitor is left unpowered. In microtunneling, equipment is often stored between projects for months at a time, increasing the risk of capacitor failure when the system is restarted.
If the dielectric layer deteriorates significantly, the capacitor may fail to hold a charge at its rated voltage. Attempting to apply full voltage to such a degraded capacitor can lead to an internal short circuit. This failure may draw excessive current and damage the VFD’s bridge rectifier, potentially rendering the drive inoperable and requiring costly repairs or replacement.
Preventative Maintenance Recommendations
Fortunately, this risk can be mitigated with simple preventative practices:
- Power-up VFDs periodically: Energize VFDs at full rated voltage for 1–2 hours at least once every 12 months.
- Follow capacitor reforming procedures: If a VFD has been unpowered for more than 12 months, consult the manufacturer’s capacitor reforming procedure. These typically involve applying a lower input voltage in a controlled, stepwise manner to gradually restore the dielectric layer’s integrity.
Gradual voltage application allows the dielectric to rebuild before full voltage is applied, preventing shorts and extending the life of the capacitors and the VFD overall.
Conclusion: A Universal Best Practice
While this article focuses on microtunneling applications, the principles discussed apply to virtually all VFDs, regardless of manufacturer or industry. Electrolytic capacitor degradation during long-term storage is a known limitation, and periodic power-up or proper reforming is a universal best practice. To ensure safe and reliable operation, always consult the VFD manufacturer’s documentation. Understanding and following these guidelines can help extend the life of your equipment and avoid costly downtime.
About Weston Alberts
Weston Alberts brings over 20 years of industry experience to Akkerman, where he has been an integral part of the team the past eight years. With a career centered on control systems, power transmission, and automation, Weston’s expertise helps drive innovation and precision in every project he touches. He holds a Bachelor of Science in Electrical Engineering from Michigan Technological University (BSEE, MTU) and is a Certified Fluid Power Hydraulic Specialist through the International Fluid Power Society (CFPHS, IFPS). Weston’s strong technical foundation and commitment to excellence make him a trusted resource and a valued member of the Akkerman team.
Akkerman Showcases Trenchless Solutions at The Utility Expo
Akkerman was proud to exhibit at The Utility Expo in Louisville, Kentucky, where Chris Sivesind and Matt Kressin from Sales joined Nathan Lindeman from Engineering to connect with customers, partners, and industry peers. The team highlighted Akkerman’s innovative trenchless solutions, discussed upcoming projects, and gathered valuable insights from utility and underground construction professionals across the country. Looking forward to the next show in 2027!
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