Internal Arc Fault

in Medium Voltage Switchgear and their Buildings


For the oper­a­tors of elec­tri­cal switchgears, the reli­a­bil­i­ty of the sys­tem is an essen­tial char­ac­ter­is­tic. An extrem­ly crit­i­cal oper­a­tional con­di­tion is the arc­ing load in the event of a short cir­cuit. The pro­tec­tion of per­sons and sys­tems in the case of an arc fault is giv­en great atten­tion by sys­tem man­u­fac­tur­ers and oper­a­tors despite the low prob­a­bil­i­ty of a fault occur­ring. An arc fault in medi­um-volt­age switchgear can lead to con­sid­er­able pres­sure and ther­mal stress on the switchgears, the switchgear build­ing and endan­ger the oper­at­ing per­son­nel. Today, the arc resis­tance of fac­to­ry-fab­ri­cat­ed switchgear pan­els is gen­er­al­ly ver­i­fied by a type test. For switchgear rooms, DIN EN 61936–1 requires that the inter­nal pres­sure in the event of a short-cir­cuit arc must be tak­en into account in the con­struc­tion of the building.


  • error prob­a­bil­i­ty in medi­um-volt­age switchgears

  • require­ments for pre­fab­ri­cat­ed met­al-enclosed switchgear and switchgear build­ings, min­i­mum require­ments for exist­ing open switchgear

  • char­ac­ter­is­tic val­ues for arc faults

  • pres­sure devel­op­ment in air-insu­lat­ed con­trol panels

  • deter­mi­na­tion of arc pow­er from arc cur­rent and arc volt­age — depen­den­cies on pan­el geometry

  • basics of pres­sure calculation

  • per­cent­age of arc pow­er used to increase pres­sure — trans­fer coef­fi­cient Kp

  • pres­sure relief in con­trol panels

  • dif­fer­ences in air-insu­lat­ed and SF6-insu­lat­ed switchgears

  • ther­mal stress on the pan­el enclosure

  • intro­duc­tion of dif­fer­ent pres­sure cal­cu­la­tion methods

  • test results on build­ing replicas

  • influ­enc­ing vari­ables on pres­sure devel­op­ment (arc cur­rent, arc dura­tion, encap­su­la­tion, relief openings)

  • pres­sure cal­cu­la­tion meth­ods applic­a­ble in engi­neer­ing technology

  • exam­ples and calculations

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