What is ferro-resonance and what causes it?
I have seen the term ferro resonance used in a few answers on this site recently and I had not heard of it before. The term doesn't have a Wikipedia page, and my web searching doesn't seem to come up with any scientific explanation of the phenomenon (though I did find a few definitions of what it is).
- sarayuLv 71 decade agoFavorite Answer
Ferro-resonance can generate overvoltages of upto 12 times line to ground source voltage upon opening a single phase device or poorly synchronised 3 phase device. Voilent failure can occur exposing personnel to the high voltage failure and accompanying conditions. Ferro-resonance conditions can result in damage to lightning arresters, switching devices, buried cable, transformers and associated equipment.
Ferro-resonance can be initiated when all of the following elements are present and the switching means at the dip point or takes off when a single phase device or an unsynchronised 3 phase device that does not operate all phases within 1/2 cycle.
1.System grounded at the source, but with no ground at the transformer bank
2. Shielded cable length or overhead conductor length sufficient to create the capacitance necessary
3. Transformer size that permits saturation of the iron core at the operating voltage
4. Transformer unloaded or lightly loaded.
Prevention or control of ferro-resonance can be by:
1. Using wye-wye transformer withboth neutrals grounded and tied to systems neutral
2. Using only phase-to-neutral (not phase-to-phase) transformers connections for single pahse transformers.
3. Limiting length of underground cable
4. For poorly synchronised switching devices, extra resistive load of 2% of the transformer capacity on underground cable.
- 1 decade ago
Assuming we are talking CV transformers, a ferroresonant transformer is a transformer designed with a very low leakage inductance and fitted with a tuned circuit in the secondary magnetic circuit.
The secondary is tuned to just below resonance at the operating frequency and is designed to operate on the edge of saturation under normal line conditions.
In the event of over voltage on the input side the secondary core moves further into saturation which tunes the tank circuit thus pushing the secondary core further into saturation and stabilising the output voltage.
Under voltage has the opposite effect, and short dropouts are covered by the energy from the resonant circuit.
The leakage inductance means that they are inherently current limiting and thus make great battery charger front ends, as well as finding use in powering critical IT and telecoms.
The downsides are that they are heavy, hum and generate large magnetic fields.
I refer you to http://www.aelgroup.co.uk/index.php?name=hb/hb006.... for the gory details.
- 1 decade ago
Ferroresonance is just the interaction of the inductance of a transformer with the capacitance of the circuit, forming a temporary series resosnant circuit that can cause a esclade of the voltage in that system.Source(s): Electromagnetic transients class notes.
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- Anonymous4 years ago
Sorry I can't give you the specs, but I'm sure you could get the power factor to unity with the right capacitors, or as near as damn it. Of course, to keep the power factor at unity, you'd need a supply voltage kept very stable, something that's not easy to do!
- 1 decade ago
Excellent answer SARAYU, I commend you on your comments.
Barrie66 Electrical engineer with 40 years experience