Cahier technique n° 190
s Merlin Gerin s Modicon s Square D s Telemecanique
“Cahiers Techniques” are a collection of documents intended for engineers and technicians people in the industry who are looking for information in greater depth in order to complement that given in display product catalogues. These “Cahiers Techniques” go beyond this stage and constitute pratical training tools. They contain data allowing to design and implement electrical equipement, industrial electronics and electrical transmission and distribution. Each “Cahier Technique” provides an in-depth study of a precise subject in the fields of electrical networks, protection devices, monitoring and control and industrial automation systems. The latest publications can be downloaded on Internet from the Schneider server. code: http://www.schneiderelectric.com section: mastering electrical power Please contact your Schneider representative if you want either a “Cahier Technique” or the list of available titles. The “Cahiers Techniques” collection is part of the Groupe Schneider’s “Collection Technique”.
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Philippe FERRACCI Graduated from the Ecole Supérieure d’Electricité in 1991, where he defended a PhD on the resonant earthed system in cooperation with EDF - Direction des Etudes et Recherches. He joined the Groupe Schneider in 1996, and is currently conducting advanced studies in the electrotechnical and electrical power system fields.
ECT190, first issued March 1998
CVT: Capacitor Voltage Transformer (IEC 186) Voltage transformer comprising a capacitor divider unit and an electromagnetic unit designed and interconnected so that the secondary voltage of the electromagnetic unit is substantially proportional to and in phase with the primary voltage applied to the capacitor divider unit. Irrational number (not fractional) Number which cannot be expressed as the quotient of two integers ( 2 , 3 , π ...). PIM: Permanent Insulation Monitor A device designed to indicate (by an audible or visual signal) the appearance of the first earth fault of a live part. VT: Voltage transformer (IEC 50) Instrument transformer in which the secondary voltage, in normal conditions of use, is substantially proportional to the primary voltage and differs in phase from it by an angle which is approximately zero for an appropriate direction of the connections.
Cahier Technique Schneider n° 190 / p.2
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.
1 Introduction 2 Understanding ferroresonance 3 Identifying ferroresonance 2.1 Resonance 2.2 Ferroresonance 3.1 Diagnosis elements 3.2 Examples of electrical power system situations favourable to ferroresonance 4 Preventing or damping ferroresonance 5 Studies for...