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 7 According to a 2019 article by Kanthal, an estimated 80% of the fuel used for heat treatment could ultimately be replaced by electricity and drastically reduce CO2 emissions. “When you burn something that contains carbon, you get carbon dioxide that you either need to take care of, or release into the atmosphere. With electric heating, you don’t have any exhaust.”[1] Pricing still is an issue between electric heating and gas heating solutions in various parts of the world, although this has narrowed over the past decade[2]. In addition, there are more options to reduce the cost further by leveraging renewables as part of the grid infrastructure (e.g., solar and current incentives). However, be aware that grid security and usage profiles could potentially negatively impact costs. The following sections examine further steps to improve the cost and efficiency of electrical heating methods based on recent technology developments. INDUSTRIAL POWER SUPPLIES Efficient use of electrical energy is expressed in terms of power factor (PF), which ranges between zero and one. A PF of one is also known as unity. Power factor is a ratio of the amount of real power (kW) to apparent power (kVA) and represents how much real power electrical equipment utilizes. Working, or real power, performs the actual work of creating heat. However, inductive loads also need a second type of power known as reactive power, measured in kilovolt-amps reactive (kVAr), to sustain the magnetic field inherent to inductive loads. When combined, working and reactive power form apparent power (measured in kVA). The power factor is calculated: where PF is the power factor, and P (kW) and S (kVA) are the real power and the apparent power, respectively. For example, a 1000 kW load with a PF of 0.7 would require 1429 kVA apparent power. A LOOK AT MODERN HEATING METHODS TO REDUCE CARBON FOOTPRINT Developments in energy management technology for electric vacuum furnaces. Peter Sherwin* Eurotherm, Ashburn, Virginia Electrical equipment is sized to handle the apparent power. Low PFs (high losses) require larger conductors, transformers, and other electrical distribution equipment to meet the final load requirements. Most utility companies apply a surcharge when the power factor goes below 0.9. This charge differs across the country and varies by provider. Some of this is hidden in additional charges, but usually, a line-item with KVA or KVAr charges will start to indicate where PF is impacting energy costs. Industrial power supplies for heat treat furnaces are expected to have a life expectancy of 20 years, or more, and reliability has been the paramount consideration in selecting power technology for vacuum furnaces[3]. Power-supply efficiency is now getting more attention as newer technology can satisfy life expectancy, efficiency, and investment. VRT POWER SUPPLY Since the 1960s, the variable reactance transformer (VRT) has been the workhorse power supply for the heat treatment industry. Battle-tested, these robust units can outlast most components on a vacuum furnace. The VRT uses an analog silicon-controlled rect- ifier (SCR)-driven direct current (DC) control winding to indirectly regulate the output power from the secondary winding of the transformer to the heating elements (Fig. 1). Specific electrical components can drift over time and lead to changes in power control behavior during the installation’s life. At full demand, a VRT can climb to a PF *Member of ASM International 5 Fig. 1 — Schematic of a VRT power supply.
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