Title :
Evaluation of AC axial magnetic fields needed to prevent anode spots in vacuum arcs between opening contacts
Author :
Schulman, M. ; Bindas, John A.
Author_Institution :
Sci. & Technol. Center, Westinghouse Electr. Corp., Pittsburgh, PA, USA
Abstract :
The influence of AC axial magnetic (AM) fields on the development of half-cycle drawn vacuum area is described. A Helmholtz coil provided an independent AC AM field Baxac in the opening gap between flat profile, butt type, Cr-Cu contacts. For peak arc currents Ip up to 20 kA, critical fields Bcritac were determined which prevented anode involvement. The dependence of Bcritac on Ip is compared with the analogous dependence using constant magnetic fields Baxdc. The results are used to extend the usefulness of the Bcrit parameter to the design of contact structures which produce self-generated axial magnetic fields from the AC arcing current. A similar direct transition to the diffuse arc mode occurs without an imposed Bax for separation currents Is <7 kA and Ip<10 kA
Keywords :
circuit-breaking arcs; coils; electrical contacts; magnetic fields; vacuum arcs; vacuum interrupters; 7 to 20 kA; AC axial magnetic fields; CrCu; Helmholtz coil; anode spots; butt type contacts; constant magnetic fields; diffuse arc mode; flat profile contacts; half-cycle drawn vacuum area; opening contacts; peak arc currents; self-generated fields; separation currents; vacuum arcs; vacuum interrupters; Anodes; Bridge circuits; Coils; Interrupters; Magnetic fields; Magnetic separation; Medium voltage; Switchgear; Vacuum arcs; Vacuum technology;
Conference_Titel :
Electrical Contacts, 1993., Proceedings of the Thirty-Ninth IEEE Holm Conference on
Conference_Location :
Pittsburgh, PA
Print_ISBN :
0-7803-1270-8
DOI :
10.1109/HOLM.1993.489668