By hvhipot 
During the operation of the circuit breaker, it is not only subject to mechanical force, electricity, heat, etc., but also to the influence of the natural environment. It is required to be able to work stably for a long time and have sufficient electrical and mechanical life. Under certain conditions, the temperature rise of each part of the circuit breaker is required to not exceed the allowable temperature value that damages the electrical performance to ensure that the electrical insulation is not destroyed and can withstand the maximum operating voltage of the system, internal overvoltage and external lightning overvoltage. Sufficient short-circuit fault closing capacity can reliably break rated current and various fault currents. in short. The circuit breaker mainly plays two roles in the power grid:
Control function: According to the needs of grid operation, use circuit breakers to put some electric equipment or lines into or out of operation.
Protection function: When the power line or electrical equipment fails, the circuit breaker can quickly cut off the connection between the faulty part and the power grid to ensure the normal operation of the fault-free part of the power grid.
In short, the circuit breaker can realize the closing and breaking of various load circuits (including transformers, transmission lines, etc.) under normal operating conditions, and can also break short-circuit faults in the line within a specified time. . Realize automatic coincidence.
The reliability of electrical products has always been one of the important indicators of engineering quality. The reliability of the power grid largely depends on the reliability of various switchgear in the power grid. Once the switching equipment fails, the entire system will not work normally, or even paralyze, and the economic losses caused are often much higher than the value of the switching equipment itself. Statistics show that in the power supply and distribution system, unexpected power outages caused by circuit breakers are the most in terms of time and quantity. The economic losses caused by modern power grid accidents are no longer solely based on the harm to the system. Switch cabinets, especially circuit breakers, are one of the core components of the power grid.
On the one hand, loop resistance, as one of the most important characteristic indicators in the electrical parameters of the switchgear, is the key information for early detection of power supply abnormalities, and it is also a reliable indicator of power system performance and attenuation. When evaluating the reliability of most types of power connections and predicting failures, including circuit breakers, disconnect switches, load switches, etc., loop resistance stability testing is very effective. The size of the loop resistance directly affects the load circuit breaker rating under short-circuit conditions Temperature rise and dynamic thermal stability of working current. The change of the contact resistance value will also directly affect the reliability of the circuit breaker. s The safety of opening and closing and the operation of the circuit breaker. Specifically, if the circuit resistance of the circuit breaker increases for some reason, the original thermal balance will be destroyed, and the temperature rise of the contact part will increase, thereby increasing the resistivity of the conductor and further increasing heat generation. In the case of high current, it will cause oxidation of the contact surface and softening or aging of the supporting insulator, which will cause the circuit breaker to fail and make it unable to work normally in a short-circuit state. And the temperature rise of the contact part will increase, which will increase the resistivity of the conductor and further increase the heat generation. In the case of high current, it will cause oxidation of the contact surface and softening or aging of the supporting insulator, which will cause the circuit breaker to fail and make it unable to work normally in a short-circuit state. And the temperature rise of the contact part will increase, which will increase the resistivity of the conductor and further increase the heat generation. In the case of high current, it will cause oxidation of the contact surface and softening or aging of the supporting insulator, which will cause the circuit breaker to fail and make it unable to work normally in a short-circuit state.
On the other hand, although the loop resistance of the switchgear is relatively small, it can be seen from the table that in the case of normal high-current operation, abnormal contact resistance (generally an increase in resistance value) will also bring a lot of energy loss. In addition, the circuit resistance test is also a mandatory item in the circuit breaker factory test, type test, handover test, and preventive test. At the same time, the resistance value of the circuit breaker’s conductive circuit is an important part of the installation, maintenance and quality acceptance of the circuit breaker.