Comparison of Arc Characteristics between 2/4 Coil-type AMF Contact and 3/4 Coil-type AMF Contact

Vacuum circuit breakers are widely used in medium voltage circuit breakers. The 3/4 coil-type axial magnetic field (AMF) contact has passed type test and reaches a nominal rated current of 2500 A. However, there is a higher requirement of the nominal rated current of 3150 A. A new 2/4 coil-type contact was proposed to increase the nominal rated current. But the current interrupting capacity of 2/4 coil-type AMF contact was unknown. The objective of this paper is to compare the vacuum arc characteristics between the 2/4 coil-type AMF contact and the 3/4 coil-type AMF contact to estimate the current interruption capacity of 2/4 coil-type AMF contact. A pair of 2/4 coil-type AMF contact was used in the experiments. Contact diameter was 100 mm, and contact material was CuCr50. Full contact gap was 50 mm, and opening velocity was set as 2.4 m/s within 20 mm after contact separation. A drawn arc experiment was carried out in a L-C discharging circuit. Arcing current was ranged from 5 to 40 kA rms and current frequency was 49.2 Hz. In the experiments, the vacuum arc behaviors were recorded by a high speed CCD camera. The results show that, the resistance of single contact of the 2/4 coil-type AMF contact was 6.29 μΩ, and the contact resistance of the 3/4 coil-type AMF contact was 8.12 μΩ. Besides, the intense arc mode duration and the diffuse arc mode duration before the second current zero of the 2/4 coil-type AMF contact and 3/4 coil-type AMF contact was similar. Therefore, the 2/4 coil-type AMF contact could control the high-current vacuum arc as well as the 3/4 coil-type AMF contact. The results suggested that the 2/4 coil-type AMF contact has similar current interrupting capacity with the 3/4 coil-type AMF contact, with a higher carrying capacity of the nominal rated current.