Theory of operation

Oltronix Ferroresonant regulators


The Ferroresonant regulators, which are also known as Constant Voltage Regulators, are based on a technique in which the primary and secondary windings of the transformer are physically isolated from each other by a steel core (shunt) which significantly reduces the capacitive coupling of spikes and noise to the secondary winding.


An AC capacitor is connected to the resonant (secondary) winding of the transformer forming a tank circuit (energy is stored in the capacitor and in the magnetic circuit; the magnetic circuit is saturated every half period). This provides the resonant circuit function which contributes to the voltage regulation of the supply.


As the stored energy is more than is delivered to the load, a hold up performance is achieved in case of a disruption of the line voltage. This makes the Ferroresonant regulators capable to suppress transients on the primary to a very high degree. Transients caused by the starting of powerful machines or equipment will be suppressed and will not affect the output current. It is not unusual to find voltage peaks up to 3000V at the primary under such circumstances.


The output wave form is rectangular, which is excellent for a subsequent rectification. Standard square wave output requires less filtering than linear transformers for DC applications.

In case of AC output the wave will have a sinus form.


Ferro resonant regulators are able to provide a nearly constant average output voltage, even when there is a widely varying input voltage. They can operate with an input voltage range as low as ±40% (depending on the load) or more of the nominal voltage. The output power factor remains in the range of 0.96 or higher from half to full load.


Ferro resonant systems provide exceptional reliability under extreme operating conditions and drop-outs are very rare. The systems are completely non-affected by other surrounding electrical systems.


This tight regulation and his reliability is advantageous to branches like the cable television, spreader builder, gas industry and heavy industry, as the active devices are protected from dangerous voltage fluctuations. Another unique feature of the ferroresonant transformer is its ability to provide current limiting in the event of a short-circuit. This effect is called foldback. The Ferro systems are good surge suppressors, and provide an inherent short-circuit protection and are not sensible to input overloads (like in case of lightning strikes) which are effecting the input voltage. The transformer’s output current can typically reach 150% of the nameplate output current rating for a short period of time without damage to the transformer. When the transformer reaches the saturation point, the output current will decrease (foldback on itself) to a minimum value, and thereby provide current limiting.


Designs based on a ferroresonant transformer are extremely rugged and reliable, and offer many years of trouble-free operation. Oltronix non-standby power supplies are extremely efficient, and have a typical efficiency rating of >90% at full load.


Copyright 2012-2019 | Oltronix IPS B.V.