The effect of serrations on the electrical contacts in contactors

Introduction of serrations on the electrical contacts in low voltage contactors has been studied. By using serrations a number of well defined a-spots are formed distributed evenly over the complete contact surface. In contrast, flat contact surfaces typically result in a-spots distributed along the edges of the contacts. The distributed a-spots of the serrated contacts lead to a more evenly distributed heat formation over the surface, compared to using flat contact surfaces, when the contactor is connected to resistive loads and is in the closed state. The even heat distribution decreases the thermal load, hence reducing the temperature increase at the terminals of the contactor. In making operations the serrations and the well distributed a-spots result in decreased blow-off force since the current is distributed on many defined paths. Further, serrations have also proven to decrease the welding forces in the first critical operations of a contactors life. By introducing serrated contacts in a contactor the temperature at the terminals decreased with roughly 12°C, enabling significant upgrading. Together with another improvement, this has been used to upgrade a contactor in rated current for AC1 duty from 1050 A to 1250 Å.