Contact connections are included in all electricalChains and are very responsible elements. The condition of electrical contact connections depends on the trouble-free operation of electrical wiring and electrical equipment.
In this case, the value of the contact resistance is important.
In an electrical circuit, at the point of contactTwo or more conductors, an electrical transition contact is created, or a conductive connection through which the current flows from one part to the other. With a simple application, the contact surface of the conductors being connected does not give a good contact. The real contact area is several times smaller than the entire contact surface, confirmation of which can be seen with the help of a microscope.
In view of the small contact area, the contactThe connection gives a very noticeable resistance when passing a current from one surface to another and is called a transient contact resistance. The contact resistance itself is a priori greater than the resistance of a solid conductor of the same shape and dimensions.
Factors affecting the value of the transient resistance
The resistance of the contact zone does not depend on the sizeContact surfaces and is determined by the force of pressure or the force of contact pressing. A contact pressing is the force with which one contacting surface acts on the other. In general, the magnitude of the pressing force and the strength of the contact material will determine the total area of contact. The number of contacts in the contact always grows when pressed.
At low pressures, a plasticDeformation of the contact, with the vertices of the protrusions crumpled and then, as the pressure increases, more and more points come into contact. As a result, the pressure should be quite large to provide a small transient resistance, but should not cause plastic deformation in the contact metal, leading to its destruction.
The transition resistance is largelyDepends on the degree of oxidation of the contact surfaces of the connected conductors. Regardless of the conductor material, the oxide film creates a greater electrical resistance.
The intensity of oxidation of conductors depends on the contact temperature and the faster it is, the greater the resistance.
Aluminum conductors are highly susceptible to oxidation. For example, the oxide film formed in air has a resistivity of 1012 ohm-cm.
Since the property of a contact connection,change. Only a new, well-treated and sheared transition contact can have the smallest possible contact resistance at sufficient pressure.
When forming contact compounds,Different ways of fastening the conductors. For example, soldering, welding, crimping, mechanical connection with bolts, and also bringing into contact by means of elastic pressing of springs.
In fact, with any method of connecting wiresIt is possible to achieve an invariably small transition contact resistance. It is important, at the same time, to connect the wires strictly according to the technology and using the necessary tools and materials for each method of connecting the wires.
The contact connection of electrochemically incompatible conductors is the contact of two oxides, which will have a high value of the transient resistance.
In order to reduce the transitional contactResistance take into account all the above factors that affect its magnitude and conduct the correspondence of types of connecting contacts to the materials of conductors and the conditions of their operation.