Modeling contact erosion in three phase vacuum contactors

A computer model was developed to simulate the unequal contact erosion measured in a vacuum contactor during three-phase AC-4 life testing. The model showed that the contact erosion rate was directly affected by the randomness of the opening time of the contacts. A probability distribution was created to simulate any degree of randomness in the opening. The model showed that repeated opening of the contactor at or near the same electrical phase angle over thousands of operations resulted in unequal contact erosion for each pole due to differences in arc energy. If there is a consistent imbalance in the arc energy one pole will erode at a significantly higher rate than the other two poles. The degree of unequal wear was dependent on the degree of randomness of contact part. The resulting unequal contact erosion would just amplify the unbalance with each subsequent operation leading to a run-away condition. A completely random opening resulted in even contact wear while synchronous opening resulted in unequal erosion. Synchronous opening of a contactor can occur from the inherent nature of the electromagnet used to operate the contactor. This model could also be used to simulate air contactor erosion.