Disconnector contacts must remain closed during the conduction of the maximum short-circuit current. This is verified in a peak-current withstand test with a full asymmetrical-current peak, a test duration of typically 0.2 s, and short-time current test with a standard duration of 1 s, as specified in IEC 62271-102.
Due to the very high electrodynamic forces, contacts naturally tend to repel unless a special design is applied using the inherent forces to achieve even more tight contact. Especially for pantograph disconnectors, the design must prevent any permanent deformation owing to the forces of contraction. Since the electrodynamic force is proportional to the square of the instantaneous current the correct representation of the asymmetrical peak is essential in the peak-current tests.
Arcing must be avoided as this increases the contact resistance and may lead to welding of the contacts. Thermal withstand is verified in the short-time current test. Figure shows a pantograph disconnector contact under the passage of high short-circuit current.
