Internal Arc

Pressure Rise due to an Electric Arc

The reli­a­bil­i­ty of elec­tri­cal equip­ment and devices is an essen­tial qual­i­ty char­ac­ter­is­tic for their oper­a­tors. Stress caused by an inter­nal arc in short-cir­cuit cas­es is an extreme­ly crit­i­cal oper­a­tional con­di­tion. Despite low prob­a­bil­i­ty of fault, switchgear man­u­fac­tur­ers pay great atten­tion to pro­vide pro­tec­tion for both peo­ple and equip­ment (switchgear and hous­ing) against arc faults. Cal­cu­la­tions to eval­u­ate pres­sure rise in inter­nal arc cas­es are a valu­able tool for this purpose.
Arc faults in medi­um-volt­age switchgears can lead to con­sid­er­able pres­sure rise and ther­mal stress for switchgear and build­ing, such as dan­ger for staff and passer­bies. The arc´s pow­er loss depends on the giv­en grid topog­ra­phy and elec­trode lay­out and caus­es a rapid heat up of the iso­lat­ing gas­es enclosed in the sys­tem (usu­al­ly air, SF6 or N2/SF6 gas mix­tures). The devel­oped heat fur­ther­more caus­es a pres­sure rise inside the switchgear. Due to tech­ni­cal rea­sons an imme­di­ate shut­down of the affect­ed sys­tem is not pos­si­ble. This results in arc times between a few mil­lisec­onds and a max­i­mum of three sec­onds. The tech­ni­cal imple­men­ta­tion of the switchgear demands a cus­tomized con­struc­tion to avoid dan­ger for peo­ple in close prox­im­i­ty. Over the last twen­ty years we have gained both the­o­ret­i­cal and prac­ti­cal expe­ri­ence in the field of inter­nal arc faults. We can offer the fol­low­ing services:

  • cal­cu­la­tion of pres­sure ris­es in switchgear and building

  • deter­mi­na­tion of the opti­mum pres­sure relief area

  • con­struc­tion hints for hous­ings (based on pres­sure devel­op­ment and blowing)

  • eval­u­a­tion of inter­nal arc tests

  • improve­ment of active and pas­sive arc safety

  • anal­o­gy con­clu­sions between cal­cu­la­tions and arc tests

Effects of an accidental arc in a substation

Fig. 1 Effects of an acci­den­tal arc in a substation

Example of an Arc power

Fig. 2 Exam­ple of an Arc power

Example of an overpressure in the fuctional unit

Fig. 3 Exam­ple of an over­pres­sure in the fuc­tion­al unit

Example of an overpressure in the building

Fig. 4 Exam­ple of an over­pres­sure in the building

In addi­tion we offer the pur­chase of our soft­ware Pres­sure. With this you can make your own cal­cu­la­tions for pres­sure devel­op­ment in inter­nal arc cases.

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