FEATURE A D V A N C E D M A T E R I A L S & P R O C E S S E S | M A R C H 2 0 2 3 4 9 angle firing. Reactive power consumption dramatically decreased from 6600 kVArh to 550 kVArh per day, which equals a 90% reduction in reactive power. The heat treatment shop PF increased from 0.70 to better than 0.90. Case 2: An advanced SCR power supply utilizing hybrid firing replaced an existing VRT power supply. After many years of operation with the advanced SCR, the PF is still better than 0.9 across the entire power range. There has been reduced maintenance time and cost and improved process repeatability. The furnace uniformity class has improved. Peak demand charges have reduced, and energy-saving averages 11%. The energy savings alone achieve a two-year payback on investment without factoring in the added savings from the improvements in product quality and lower maintenance costs. MFDC POWER SUPPLIES A recent development in the heat treating industry is the introduction of MFDC (mid-frequency direct current) power supplies incorporating insulated-gate bipolar transistor (IGBT) technology (Fig. 5). This technology was initially designed for industrial welding machines to provide a compact solution for mobile robot welders[5]. However, the reduction in the size of the transformer and DC power supply offers some benefits in the welding industry to help offset the initial cost of the solution when compared to conventional welding solutions. IGBTs are also used in power converters used in wind turbines and have been studied extensively due to reliabil- ity issues[6]. As a result, there is currently significant investment in analytics to help identify the remaining useful life of these items to enable timely replacement and avoid turbine shutdowns for excessive periods. A recent case study focused on energy cost savings achieved with MFDC versus a conventional VRT solution[7]. This demonstrates significant cost savings for certain types of heat treatment cycles. DIGITAL TOOLS Advanced SCR technology and MFDC power supplies offer the potential for further optimization with digital tools. Digital communication via industrial protocols can tighten the integration between the power supply and the furnace control system, maximizing the responsiveness and accuracy of the energy loop. The power supplies can also provide a level of diagnostic information on energy use, help troubleshoot maintenance issues, and even extend to provide some early warning of heating element damage or deterioration. Advanced SCRs also provide the option for distributive load management. By leveraging the gaps in the cycles (in burst firing), peak power loads can be managed across several electric furnace installations. Advanced power forensics from energy supply management software can help identify power event causes and event patterns to enable better proactive maintenance. The plant system capacity is tracked to avoid overload and failures and manage backup power systems. The system can be used to help avoid power factor and peak demand penalties and even help identify billing errors. Consumption patterns from all utilities can be provided (water, air, gas, electric to steam) and costs are allocated to departments or processes to aid more accurate quoting and billing. CONCLUSIONS The heat treat industry now has several options for power supply technology. VRTs have been the primary technology source with proven reliability but inherent issues of poor energy efficiency. SCRs have developed over the past 40 years to be a reliable and competitive offer and now can provide efficient solutions with hybrid firing and management of peak loads. MFDC technology is still relatively new in the heat treat world; indeed, there are early signs of energy savings but also some concerns around the robustness of the technology in a heat treat environment. It will be interesting to watch the development of these solutions over the next decade and see how much impact new technology can have in aiding efficient heat treatment for the benefit of all. ~HTPro For more information: Peter Sherwin, global business development HT, Eurotherm US LLC, 446210 Guildford Dr., Suites 100-120, Ashburn, VA 20147, 571.246.3809, peter. sherwin@watlow.com. 7 Fig. 5 — Simplified MFDC topology.
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