Ferroresonant power supply
A ferroresonant power supply is very similar to an unregulated power supply except for the characteristics of the ferroresonant transformer.
The ferroresonant transformer will supply a constant output voltage over a wide variation of the transformer input voltage. The problems with using a ferroresonant power supply include that it is very sensitive to slight changes in line frequency and would not be switchable from 50 Hz to 60 Hz, and that the transformers dissipate more heat than conventional transformers. These power supplies are heavier and will have more audible noise from the transformer resonance than regulated linear power supplies.
Ferroresonance occurs when an unloaded 3-phase system consisting of an inductive and a capacitive component is interrupted by single phase means. In practice this is typical of a high voltage electrical distribution network of transformers (inductive component) and power cables (capacitive component). If such a network has no load and the applied voltage is then interrupted on a single phase, a ferroresonance may be observed. If the remaining phases are not interrupted and the phenomenon continues, failure of connected components can occur due to the breakdown of insulation due to overvoltage.
The phenomenon can be avoided by maintaining a minimal load on the circuit or by interrupting the applied voltage by a 3-phase interrupting device.
Other definitions and resources for information about power supplies
Power supply used at higher power levels in fixed applications, since they are very heavy. Can only be used effectively when the line frequency is very stable as they are sensitive to variations of input AC frequencies.
www.systemconnection.com/downloads/poweradapterkb/glossary.html
An open-loop voltage stabilized power supply in which a portion of the transformer core is driven into saturation by a resonant tank circuit. The output is derived from the saturated portion of the transformer and is relatively independent of input voltage.
adm.lacitec.on.ca/~ymicha/mcours/mixte/glossaire.htm