ABSTRACT
This chapter covers the operating principle, characteristics, applications, specifications, and sizing guidelines of constant-voltage transformers (CVT). Sola's first transformers for furnace-ignition systems and neon lighting, based on the unique application of ferroresonant principles, led in 1938 to his invention of the CVT. The magnetic shunt in the CVT design allows the portion of the core below the magnetic shunt to become saturated while the upper portion of the core remains unsaturated. CVT have proven to be a reliable means of enhancing voltage-sag tolerance of industrial process-control elements such as relays, contactors, solenoids, dc power supplies, programmable logic controllers, and motor starters. The ability of a CVT to regulate its output voltage is generally based upon two characteristics of the connected loads, both of which are related to current and both of which must be determined to properly size a CVT.
