Calculation of contact capacity for vacuum pressure switches

The calculation of the contact capacity of vacuum pressure switches involves multiple factors. The following is an explanation from aspects such as the calculation principle and influencing factors:

The principle of contact capacity calculation

Contact capacity refers to the rated current that is allowed to flow through the contacts of relays and switches. When calculating the contact capacity of a vacuum pressure switch, it is necessary to consider the current and voltage that the contacts can withstand in the closed state, as well as the influence of factors such as contact material, shape, and contact pressure on the contact resistance.

The contact resistance is composed of the transition resistance of the contact surface and the resistance of the contact itself in series. The transition resistance of the contact surface is related to factors such as the influence coefficient of the contact material and the surface condition between the contacts, the pressure between the contacts, and the coefficients related to the shape of the contacts. For example, for point-type contacts, its correlation coefficient is 0.5; The linear contacts are 0.7 to 0.8. The planar contact is 1. When calculating, if the influence of temperature is not taken into account, the transition resistance can be calculated according to the corresponding formula. The resistance of the contact itself is determined by conventional methods, and usually its value is less than the transition resistance of the contact surface, which can be approximately ignored in calculation.

Influencing factors

Contact material: In addition to meeting the strength requirements, the selection of contact material should also have good electrical conductivity, easy processability and a relatively small coefficient of expansion. The elastic coefficients and allowable extrusion strengths of different materials vary, which will affect the contact area and load-bearing capacity of the contacts, and thereby influence the contact capacity. For instance, materials such as soft copper, nickel, platinum, graphite, and molybdenum have different properties. When calculating the contact capacity, it is necessary to do so based on the specific material parameters.

Contact shape: The shape of the contact affects the coefficients related to the contact shape, thereby influencing the contact resistance and contact capacity. Common contact shapes include dot type, linear type, planar type, etc. Contacts of different shapes have different current distributions and contact areas when in contact, resulting in differences in contact resistance and contact capacity.

Contact pressure: Within a certain range, the greater the contact pressure, the smaller and more stable the contact resistance between the contacts. This helps to enhance the load-bearing capacity of the contacts, thereby affecting the contact capacity. Therefore, when calculating the contact capacity, the influence of contact pressure on contact resistance needs to be taken into account.