Ferroresonance also called as neutral instability is an abnormal condition wherein unstable high voltage occurs on 3 phase electrical systems that could potentially cause the failure of equipment.

Ferroresonance generally refers to a wide variety of interactions between capacitors and iron-core inductors that result in unusual voltages and/or currents Ferroresonance In power system context occurs when a nonlinear inductor is fed from a series capacitor.

Ferroresonance can occur when an unloaded 3-phase system consisting mainly of inductive and capacitive components is interrupted by single phase means. In the electrical distribution field this typically occurs on a medium voltage electrical distribution network of transformers (inductive component) and power cables (capacitive component).

Below are chosen links to further explain the phenomenon of Ferroresonance.

Cahier Technique: Ferroresonance
Ferroresonance is a non-linear resonance phenomenon that can affect power networks. The abnormal rates of harmonics and transient or steady state overvoltages and overcurrents that it causes are often dangerous for electrical equipment. Some unexplained breakdowns can be ascribed to this rare, non-linear phenomenon.

The purpose of this “Cahier Technique” is to help readers understand ferroresonance. The methods described ensure credible prediction and evaluation of the risk of ferroresonance in existing and future installations. Practical solutions designed to avoid or eliminate ferroresonance are also given. Read more...

Investigation of Ferroresonance and Switching Surge Phenomena on the Power Switchyard
When the structure of power system is changed or facing external disturbances, many unstable transient phenomena may occur during the transient period. This transient process may lead to overvoltage situation and will have some impacts on the power system.

Depending on the frequency of transient process, the transient phenomena can be broadly classified as high, medium and low frequency. The switching and lightning surges belong to a high-frequency overvoltage phenomenon. Read more...

Ferroresonance during Single-Phase Switching of Distribution Transformers
After single-phase switching-on of the first phase of an unloaded distribution transformer two identical series circuits arise each consisting of the no-load inductance of the transformer and the earth capacitance of the still open phases. These circuits are fed in parallel by the phase voltage Us.

The saturation of the no-load inductance of the transformer, however, limits the over-voltage. Resonance phenomena in such a series circuit with non-linear inductance are described by the ferroresonance theory and characterized by a 'jump' effect. Read more...

Ferroresonance Phenomenon in Power Transformers - Experimental Assessment
This paper reports on the results of recent research and development efforts to study and assess various impacts of ferroresonance phenomenon on operating performance of power transformers and to investigate ways to mitigate the effects of such phenomenon.

Three-phase core-type transformers are used in the study. The results of the technical investigation and the associated ferroresonance experimental work performed showed that ferroresonance can cause dangerous overvoltages and overcurrents in three-phase core type transformers. Read more...

Determination of the Characteristics for Ferroresonance Phenomenon in Electric Power Systems
Ferroresonance is an electrical phenomenon in nonlinear character, which frequently occurs in power system due to transmission line faults and single or more-phase switching on the lines as well as usage of the saturable transformers.

In this study, the ferroresonance phenomena are investigated under the modeling of the West Anatolian Electric Power Network of 380 kV in Turkey. The ferroresonance event is observed as a result of removing the loads at the end of the lines. Read more...

Ferroresonance is a phenomenon that involves high distorted levels of overvoltage and overcurrents. During the last decades, the three-phase ferroresonance research has suffered several changes due to the continuously changing equipment and network.

This paper analyses every main factor that is somehow related with the origin, consequences and the preventive decisions that may lead us to avoid the three-phase ferroresonance to appear. Besides this, it gives the opportunity to get a quick identification of such a complex phenomenon. Read more...

Ferroresonance Experience in UK: Simulations and Measurements
Ferroresonance is a complex non-linear electrical phenomenon that can cause dielectric & thermal problems to the transmission plant and switchgear. Electrical systems exhibiting ferroresonant behaviour are nonlinear dynamical systems.

The application of conventional linear mathematics is therefore not fully appropriate for the study of ferroresonance. Read more...


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