Research On Welding In Separation Of Electrical Contacts

Welding in contact separating operation is a strange behavior which is quiet different from the traditional dynamic welding phenomenons, i.e. dynamic welding happens during the contact separating operation rather than making operation. The research on welding in separation can help understanding the mechanism of dynamic welding and improving the design of switching devices which have requirements for better anti-welding ability and long-life. Thus research on welding in separation is meaningful.Now, the research on welding in separation is on the initial stage where it needs more improvements, especially in two aspects. The first one is that the welding experimental conditions are simple and limited. For example, in many welding experiments, the experimental voltage ranges from 13 V to 28 V and the contact pressure is always limited to a fixed value. These simple and limited experimental conditions make conclusions of the experiments less verified. The other one is that in previous welding experiments, the parameters which need to be measured were ignorant, such as the contact voltage, current, contact pressure, displacement of the movable and fixed contact, the contact material transfer and so on.To make up for the deficiency mentioned above, we establish a welding testing apparatus. The apparatus is composed of a contact analog testing device and a contact surface measurement device with is based on CCD cameras. With this apparatus, we can conduct welding experiments under various experimental conditions. Many electro-mechanic parameters can be adjusted within certain limits. For example, the source voltage can be adjusted from 1V to 270 V, the current from 1A to 100 A, the gap length from 0.5mm to 3mm, and so on. What's more, during experiments many parameters, such as contact voltage, current, contact pressure, displacement of the movable and fixed contact can be measured in real time. Meanwhile, the change of contacts gap and the height of pips with the increase of operation cycles are observed through CCD cameras. After experiments, the waveforms of all the electro-mechanic parameters can reappear with the help of LABVIEW. And the gap length and pip height on the contact surface can be calculated through MATLAB. By analyzing these waveforms and calculating the data, we can understand the certain process of the welding in separation.With this welding in separation testing apparatus, we conducted a series of welding experiments under experimental conditions of 42V/30 A, 42V/20 A and 28V/20 A. Three kinds of contact materials, AgSnO2, AgNi and AgCdO were used. The electro-mechanic parameters were measured during those experiments.With the help of procedure on the base of LABVIEW and MATLAB, the waveforms of contact voltage,current, contact pressure and displacement of contacts have been analyzed. What's more, the pictures of the contact surface shot during experiments have been analyzed. Through analysis, we get the following conclusions: 1) Dynamic welding can surely occur in contact separating operation. 2) welding in separation is always accompanied by a contact voltage pulse. We think the pulse is caused by the mental bridge between the two contacts rather than contact bounce. 3) The mechanism of the welding in separation is that arcs ignited by contacts separating causes fierce material transfer between two contacts, which finally become metal bridges. After the solidification of metal bridges, welding happens. 4) With the increase of the number of operations, the increase of pip height on the contact surface will fluctuate. Meanwhile, the decrease of the gap length will fluctuate,too.