Three Phase Solid State Relays in Heating Circuits

This white paper discusses Three Phase Solid State Relays (SSRs) and their applications in three-phase heating circuits. It begins with an overview of SSRs, highlighting their function and the differences between single-phase and three-phase relays. The paper emphasizes the importance of understanding three-phase power systems and the characteristics of common heating loads when selecting SSRs for heater control applications. It details the attributes of SSRs, including contactless operation, high-speed switching, and low input control power requirements. The document also explains the configurations of three-phase heating loads, specifically delta and wye configurations, and provides formulas for calculating power and current in these systems. Additionally, considerations for incorporating SSRs in three-phase applications are outlined, including thermal management and electrical transients. The paper concludes by discussing the selection criteria for SSRs in resistive heating applications, noting the straightforward nature of these applications compared to motor loads.