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 grid. Once the switching device malfunctions, the entire system will not function properly or even become paralyzed, resulting in economic losses that are often much higher than the value of the switching device itself. Statistics show that in the power supply and distribution system, unexpected power outages caused by circuit breakers are the most frequent 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. The switchgear, especially the circuit breaker, is one of the core components of the power grid.
On the one hand, circuit resistance, as one of the most important characteristic indicators in the electrical parameters of switchgear, is the key information for early detection of power supply abnormalities and the most reliable indicator of power system performance and attenuation. When evaluating the reliability and predicting faults of most types of power connections, including circuit breakers, isolation switches, load switches, etc., loop resistance stability testing is the most effective. The size of the loop resistance directly affects the temperature rise and dynamic thermal stability of the working current under short-circuit conditions at the rated value of the load circuit breaker. The change in contact resistance value will also directly affect the reliability of circuit breaker opening and closing and the safety of circuit breaker operation.
Specifically, if the circuit resistance of the circuit breaker increases for some reason, it will disrupt the original thermal balance, increase the temperature rise of the contact part, and thus increase the resistivity of the conductor, further increasing heating. Under high current conditions, it can cause oxidation of the contact surface and softening or aging of the support insulator, leading to circuit breaker failure and preventing it from working properly under short circuit conditions. And the temperature rise of the contact part will increase, which will increase the resistivity of the conductor and further increase the generation of heat.
On the other hand, although the circuit resistance of the switchgear is relatively small, it can be seen from the table that under normal high current operation, abnormal contact resistance (usually an increase in resistance value) can also cause a large amount of energy loss. In addition, circuit resistance testing is also a mandatory item in circuit breaker factory testing, type testing, handover testing, and preventive testing. At the same time, the resistance value of the conductive circuit of the circuit breaker is an important part of the installation, maintenance, and quality acceptance of the circuit breaker.
