May 2022 Volume 4

EQUIPMENT & TECHNOLOGY

Conclusion The mechanical aspect of a large power supply cannot be overlooked during preventative maintenance. Bolted connections require maintenance, and proper assembly is a key factor. It has been shown that even a small amount of contact resistance can cause bolted connections to fail. Neglecting to perform mechanical maintenance can result in high repair costs and extended down-time. However, following OEM recommendations, applicable standards, and best practices will keep any induction heater in tip-top shape. Additionally, consideration of the physical environment is crucial when determining what type of and how often maintenance activities should be carried out. Josh Carney Technical Director Integral Power Technologies, LLC Phone: 440-701-6022 Email: jcarney@integralpowertechnologies.com

Many original equipment manufacturers of high current power supplies recommend that bolted connection hardware is re-torqued after the first three months following installation: this handles the fastener creep and loosening during transport if not done during commissioning. Also important is maintenance frequency. Some programs specify that every nut and bolt should be checked for tightness on a quarterly basis. For certain situations this is logical, but for others where there is no significant vibration, this level of attention is excessive. The key is understanding what factors are affecting the equipment in-situ . Using Available Standards and Best Practices: Using ANSI/NETA Giving attention to bolted connections in power systems is not a novel concept. For a number of years bodies such as the InterNational Electrical Testing Association (NETA) and American National Standards Institute (ANSI) have published standards for maintaining electrical power equipment and systems. Just as the ANSI/NETA standards have contributed to the reliability of our electrical power grids, applying these standards to induction heating equipment will have the same results. Using Torque Tools and Proper Assembly If the maintenance program has personnel check and re-torque fasteners at a regular interval, it is highly recommended that a calibrated torque wrench be used. As much as under-tightening is a problem, over-tightening is a bigger problem. Oftentimes maintenance technicians use a process where they tighten the fastener until it stops then go ‘just a little bit more’ to make it ‘tight'. The problem is that a bolt tightened ‘just a little bit more’ could exceed the yield strength of the fastener during a thermal cycle. Then what will you have? A broken fastener and a big problem.

Image 10: As shown on this resonant capacitor: make certain that hardware is properly torqued. Photo courtesy of Integral Power Technologies, LLC

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