Current commutation in arcless interruptions with PTC (positive temperature coefficient resistivity)

In most existing current interruption devices, the current is interrupted using only separating contacts. By adding a ceramic PTC (CPTC) element in parallel with the contacts, 100% of the interruption energy can be converted to heat, eliminating the arc totally. The initial voltage across the contacts must be less than a predetermined value in order to shunt all of the current to the CPTC. The cold resistance of the CPTC is the main factor in determining the initial voltage across the contacts and the current at which the CPTC trips. A ceramic PTC device was tested with cold resistance of 14 /spl Omega/. At 300 V/sub DC/ and 1.0 A, 100% of the interruption energy was consumed by the CPTC. All the current commutated from the contacts to the CPTC within 0.2 /spl mu/s. At 300 V/sub DC/ and 0.5 A, the current commutated to the CPTC within only 0.1 /spl mu/s. A high speed video camera observed that current commutation was completed before the actual separation of the contacts. No arc was seen by the high speed video camera. No voltage spike was induced by the inductance. Due to the elimination of arcing, use of the CPTC in low current interruption devices will result in reduced contact size and increased operation cycles. It will also provide an arcless interruption for application in hazardous conditions, and can also be applied to 42 V automotive systems.