Ferroresonant Transformers

Ferroresonant transformers (also known as “ferros”, constant voltage transformers, or CVT’s) utilize a special magnetic structure and a capacitor to achieve voltage regulation and current limiting. Ferros may be designed to provide a quasi-square wave output, which can be readily rectified and filtered for a smooth d-c output; or they can be designed for a low distortion sine wave output. These transformers are single phase devices, but they may be used in combinations of two or three for three phase applications (see three phase applications page).

Because ferroresonant transformers are constructed of steel and copper, they are extremely rugged and reliable. Conventional ferros are not dependent upon electronic control circuits, although a specialized type known as a controlled ferro, does use electronic control to provide precise and adjustable regulation of output voltage.

Conventional ferros have a fixed output voltage (governed by the design) and can readily provide line and load regulation to within 3%. Controlled ferros can be designed to have an adjustable output voltage, with regulation dependent upon the design of the control circuitry. Regulation to better than 1% can be achieved.

Current limiting is an inherent benefit of ferroresonant transformers. If an extreme overload or even a short circuit is applied, secondary current is limited to a safe level and primary current is actually lower than at normal full load.

In addition, the structure of a ferro provides a low-pass filter, which combined with the voltage regulating characteristics, results in very high suppression of transient and surge voltages. A ferro is unsurpassed as a device for protecting sensitive loads from transients, noise, surges, and other disturbances on the power line. The energy stored in this low-pass filter provides yet another benefit: the ferro can “ride through” brief power outages (on the order of one-half cycle or so) without loss of output voltage.

Ferroresonant Transformers

  • Regulated output voltage
  • Fixed output voltage (conventional ferros)
  • Adjustable output voltage (controlled ferros)
  • Inherent current limiting
  • Ride through of brief power outages
  • Excellent transient and surge suppression
  • Very high levels of isolation
  • Extremely robust, rugged, and reliable
  • Quasi-square wave output waveform reduces filtering requirements for d-c applications
  • Low distortion sine wave output available for a-c load applications

Typical Applications

  • Line conditioners to protect computers and other sensitive electronic devices from transients, noise, and surges on the power line
  • Power supplies
  • Battery chargers
  • Inverters
  • Pre-regulators for precise power supplies
  • Lighting

Ratings and Sizes

All of General’s products are custom designed for specific applications. Available ratings depend upon a number of factors including power requirements, maximum voltages, currents, and frequency. We can produce ferroresonant transformers with ratings from 100 va to 10 kva for 50/60 Hz operation. Please do not hesitate to inquire as to your requirements.

Please call us at 972-442-1285 or contact us for your custom constant voltage magnetic application.