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The Automatic Voltage Regulator – AVR:
Guide and Comparison

The Operation, Application and Comparison of Automatic Voltages Regulators in AC Power Applications

5 The Ferroresonant Transformer (Type) Voltage Regulator


· Constant voltage transformer

· Constant voltage regulator

· CVT

· Ferroresonant voltage regulator

· Ferroresonant transformer

· Ferro


The ferroresonant transformer or constant voltage transformer has a very long history having been invented in 1938 by Joseph Sola and continuing to sell tens of thousands of units per year. The ferro of today has had some minor improvements but remains fundamentally unchanged from the original design.

Well known for its longevity, some CVTs are found still in service after more than 40 years.  Limited to single phase applications, the ferro is slowly being displaced by small electronic voltage regulators.

Contents of this section:

5 The Ferroresonant Transformer (Type) Voltage Regulator
  5.1 Constant Voltage Transformer Operation
  5.2 Constant Voltage Regulator Characteristics
  5.3 Ferroresonant Transformer Advantages


Quick Links

1 The AC Automatic Voltage Regulator
2 Automatic Voltage Regulators and Power Conditioners
3 The Need for Automatic Voltage Regulation
4 Automatic Voltage Regulator Function
5 The Ferroresonant Transformer (Type) Voltage Regulator
6 The Mechanical (Type) Voltage Regulator 
7 The Electronic (Type) Voltage Regulator

Complete Table of Contents...