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There is a large diversity of radiated disturbancesources, normally divided into two major families:c those with a narrow spectrum: radiotransmitters, radars, induction furnaces,microwaves, etc.c those with a wide spectrum: lightning,electrostatic discharge, breaking devices,commutator motors, welding machines, arcfurnaces, etc.Note that some sources such as staticconverters and lightning are both conducted andradiated interference generators.Electronic circuits are the main victims ofelectromagnetic disturbances since they processvery low voltage signals and have largeimpedances (they consume less and less).Interference occurs on the “victim”, mainlythrough the cables entering and leaving the box(by coupling in common mode – differentialmode – common impedance – crosstalk). Also,the paths of printed circuits and components canand must be determined to ensure minimumelectromagnetic susceptibility.The most sensitive functions are:c LF amplifiers (low-pass)c Input circuits (integrators)c Logic circuits (digital).Furthermore, growth of digital communications isresponsible for new difficulties as buses create,with the electrical network, loops that aresensitive to the magnetic fields developed by thehigh electric currents and close lightning strokes.Precautions must therefore be taken for thestudy and production of installations (see “CahierTechnique” no. 187).In LV, immunity tests against radiated fields aredefined in standard IEC 61000-4-3 andsubsequent sections. Thus, the releases of theCompact circuit-breakers of Merlin Gerin brandare tested according to the maximum degree ofseverity of standard IEC 60947-2 referring tostandards IEC 61000.Finally, to better understand electromagneticcompatibility (EMC), readers can refer to “CahierTechnique” no. 149.5.2 Electrostatic dischargesThis type of disturbance affects and/or destroyselectronic switchgear, but has no impact onelectrical networks.In point of fact, electronic components areparticularly sensitive to these electrostaticdischarges as they use increasingly more“low level” components with low consumptionand high input impedance. Also, a part of theseswitchgear, e.g. indicator lights, potentiometers,is always accessible to touch.People, depending on their footwear and thefloor on which they walk, plus air humidity, canbe “charged” with a potential of up to 15 kV(phenomenon modelled and representedon figure 34 ). In this case the dischargecurrent can reach several dozen amperes(see fig. 35 )!It is thus necessary to immunise and testelectronic apparatus for these discharges. Thissubject is described in standard IEC 61000-4-2.I% IWhere U = 15 kV, which correspondsto class 4 in standard IEC 61000-4,I = 70 A in event of “ breakdown”.150 Ω902 Ω150 pF2 Ω50T10tmtFig. 34 : modelling the electrostatic load circuit of aperson.Fig. 35 : electrostatic discharge current(tm = 5 ns, T = 30 ms).Cahier Technique Schneider Electric no. 141 / p.22
6 ConclusionLV networks are very polluted as they aresubjected to numerous aggressions of varyingorigins: external (sources, MV networks, etc.),operation (elimination of faults, control by carriercurrent, etc.), applications (furnaces, electronicloads, etc.). At the same time, qualityrequirements of the “electricity” product as wellas operating dependability of electrical andelectronic equipment, whether for production,management or commerce, are increasinglygreat.c Users, aware of malfunctions and operatinglosses, are seeking to control their energy supply.They are increasingly measuring conventionalvalues (voltage, current, power, cos ϕ) andrecording overvoltages, dips and power cuts, etc.For example they also want to know:v total harmonic distortion,v harmonic level,v peak factor,v voltage unbalance ratio.c Electrical utilities have to guarantee a certainlevel of quality of the “electricity” product theydeliver (see appendix 3: standard EN 50160).c Electrical and electronic switchgearmanufacturers are obliged to comply with theEuropean directive on EMC as from design oftheir products that they then test according to thespecifications of standards such as IEC 61000(see appendix 3). However they are increasinglyoffering new products able to meet users’expectations with respect to follow-up of energyquality and distribution reliability, for example:v control units placed in circuit-breakers areused to take all measurements (I, F, P, cos ϕ,etc.),v switchboard centres are now used to knowinstantaneous, maximum and average reactiveand apparent energies and powers over aspecific period. They can also measure totalharmonic distortion, the peak factor and phaseunbalances (voltage and current).c Professional electricians (ranging fromdesigners to cable layers) must study the mainprobable disturbances in order to find the mostsuitable solutions. For example designers haveto provide emergency sources, UninterruptiblePower Supplies (UPS), surge arresters, filtersand active harmonic compensators.In this sense, for all people concerned withquality and availability of electrical powerthroughout the distribution process, this “CahierTechnique” forms an initial tool in so far as itexplains the various disturbances that can affectelectrical networks and equipment. Its purpose isto increase knowledge of these disturbances inorder to combat them more effectively.Cahier Technique Schneider Electric no. 141 / p.23
Page 1 and 2: Collection Technique ..............
Page 3 and 4: no. 141Electrical disturbances in L
Page 6 and 7: 1 LV industrial voltagesAll network
Page 8 and 9: In Francev On EHV networks (400 and
Page 10 and 11: Disturbances due to operation ofLV
Page 12 and 13: LightningLightning directly affects
Page 14 and 15: Switchgear operations and operation
Page 16 and 17: FerroresonanceThis phenomenon may o
Page 18 and 19: 3 Sine wave disturbancesVoltages (w
Page 20 and 21: Standard EN 50160 indicates, for pu
Page 22 and 23: 4.2 Phase unbalanceBesides the effe
Page 26 and 27: Appendix 1: transmission of overvol
Page 28 and 29: BibliographyStandardsc EN 50160: Vo
Page 31: Schneider ElectricDirection Scienti

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