Cahier technique n 179 - studiecd.dk

1 Cahier technique n 179LV surges and surge arrestersLV insulation co-ordinationC. S raudieCollection technique "Cahiers Techniques" is a collection of documents intended for engineersand technicians, people in the industry who are looking for more in-depthinformation in order to complement that given in product , these "Cahiers Techniques" are often considered as helpful"tools" for training provide knowledge on new technical and technological developmentsin the electrotechnical field and electronics. They also provide betterunderstanding of various phenomena observed in electrical installations,systems and " Cahier technique " provides an in-depth study of a precise subject inthe fields of electrical networks, protection devices, monitoring and controland industrial automation latest publications can be downloaded from the Schneider Electricinternet web : :Experts' placePlease contact your Schneider Electric representative if you want either a" Cahier technique " or the list of available "Cahiers Techniques" collection is par t of the Schneider Electric s"Collection technique ".

2 ForewordThe author disclaims all responsibility subsequent to incorrect use ofinformation or diagrams reproduced in this document, and cannot be heldresponsible for any errors or oversights, or for the consequences of usinginformation and diagrams contained in this of all or part of a " Cahier technique " is authorised with theprior consent of the Scientific and Technical Division. The statement"Extracted from Schneider Electric " Cahier technique " no.." (pleasespecify) is 179 first issue, March 1999no. 179LV surges and surge arrestersLV insulation co-ordinationChristophe SERAUDIEH aving graduated from the Centre d Etudes Sup rieures desTechniques Industrielles (CESTI: Centre for the Advanced Study ofIndustrial Techniques) in 1986, he then obtained his PhD in ceramicmaterials in 1990 (thesis prepared at Limoges University under aCeramics and Composites CNRS contract).

3 He joined Merlin Gerin s LV breaking research group that same year, and then in 1992assumed responsibility for development of surge arresters in theLV Final Distribution technique Schneider Electric no. 179 / mode (disturbances):which are applied and propagated between liveconductors and frames or the mode (disturbances):which are superimposed on network voltageand propagated between the various :equipment particularly designed to eliminateswitching and power frequency current Is:current delivered by the network and which flowsoff via the surge arrester after passage of thedischarge current (this phenomenon only existsfor spark-gap-based technologies).

4 Leakage current If:current flowing in the surge arrester whenit is supplied at its maximum steady of protection:the highest value of residual voltage andmaximum arcing rod:a metal device designed to intercept lightning inorder to flow it off to arcing voltage:peak voltage in s wave (characteristicspecific to spark-gap type components).Nominal In or maximum Imax discharge current:peak value of the current in 8/20 s wave(see fig. 9) used for operating voltage Ur:voltage appearing at the terminals of a surgelimiter (component or switchgear) duringdischarge current limiter:device used to attenuate or clip certain types ofsurge.

5 In France this term is particularly reservedfor MV surge protection devices in LV installationsusing IT earthing arrester :a device designed to limit transient surges,including lightning surges, and to redirect currentwaves. It contains at least one non-linearcomponent (as per NF C 61-740). Cahier technique Schneider Electric no. 179 / surges and surge arrestersLV insulation co-ordinationContents1 Surgesp. Lightning surgesp. Surges by electrostatic dischargesp. Switching surgesp. Power frequency surgesp. 92 Surge protection The protection principlesp. The componentsp. Implementation of the componentsp.

6 143 Standards and Product standardsp. Horizontal standardsp. Surge arrester installation guidesp. Implementation of surge arrestersp. 194 Conclusionp. 22 Bibliographyp. 23 Low voltage insulation co-ordination consists of matching the surge levelsthat may appear on an electrical network (or installation) with the surgewithstand of the industrial or domestic equipment that it supplies, bearing inmind the possibility of including surge limiting devices in the discipline contributes to increased safety of equipment and increasedavailability of electrical co-ordination control therefore requires.

7 C estimation of surge level and energy,c knowledge of the characteristics and location of the devices installed,c selection of appropriate protection devices, bearing in mind that fora device, there is only one surge withstand (normally defined by itsconstruction standard).This Cahier technique deals with the aspects relating to standards andimplementation of disturbances, protection devices and in particular mainly concerns LV installations (< 1000 V) in the industrial, tertiary anddomestic technique Schneider Electric no. 179 / SurgesThere are four different types of surge:c lightning,c electrostatic discharge,c switching,c power main characteristics are described in thetable infigure 1, and are defined in theIEC 1000-4 disturbances which are superimposed onnetwork voltage can be applied in two modes:c common mode, between the live conductorsand the earth,c differential mode, between the various both cases the resulting damage comes fromdielectric breakdown and leads to destruction ofsensitive equipment and in particular of are regularly subjected to acertain number of non-negligible surges(see fig.)

8 2) which cause malfunctioning andHome (living roomon 1st floor) 235 andGyr factory(furnace room)Home (service entrance)underground distributionLandis and Gyr factory (laboratory)Bank in Basel (service entrance)Farm supplied byoverhead linesComposite curve inUSA, 120 V distributionNumber oftransients/yearSurgeDurationSteepness of rising edge,Damping accordingor frequencyto distanceLightningVery short ( s)Very high (1000 kV/ s)StrongElectrostaticVery short (ns)HighVery strongdischarge( 10 MHz)SwitchingShort (ms)AverageAverage(1 to 200 kHz)At powerLong (s),Network frequencyZerofrequencyor very long (h)Fig.

9 1: the four types of surge present on the electrical 2: frequencies of occurrence and peak values of surges (recorded by Landis and Gyr and published by the IEEE). Cahier technique Schneider Electric no. 179 / Lightning surgesLightning is a natural phenomenon withspectacular and destructive France two million lightning strokes causeeach year the death of 40 people and20000 animals, 15000 fires, 50000 power cutson electrical and telephone networks and thedestruction of countless transformers andthousands of electronic household total cost of the effects of lightning isestimated at around one thousand million francsa year.

10 Not all regions have the same degree ofexposure. Although a map normally existsshowing the lightning densities for each country,in order to determine in greater detail theexposure of a site, preference should be given tothe maps published by firms specialising in thedetection of storms and related phenomena(see fig. 3).Lightning is linked to the formation of stormclouds which combine with the ground to form agenuine dipole. The electrical field on the groundmay then reach 20 kV/m. A leader developsbetween the cloud and the ground in a series ofeven destruction of equipment, resulting devices, such as HV and LV surgearresters, are available.