In the power system, the selection of switchgear for distribution cabinet is crucial, and its short-circuit current tolerance is even more related to the safe and stable operation of the entire distribution system.
First, the selection of switchgear should be based on the use scenario and load characteristics of the distribution cabinet. In the industrial field, such as power distribution in large factories, the load may include many inductive loads such as high-power motors, with large starting current and high short-circuit current peak during short-circuit faults. At this time, switchgear with high short-circuit breaking capacity and good dynamic stability should be selected, such as vacuum circuit breakers. It uses vacuum as an arc extinguishing medium, has strong arc extinguishing ability, can quickly cut off short-circuit current, and effectively protect lines and equipment. In the distribution cabinet of commercial buildings or residential areas, the load is relatively dispersed and the power is small. According to the actual situation, molded case circuit breakers can be selected, whose short-circuit breaking capacity meets the general civil power distribution requirements and the cost is relatively low.
Secondly, short-circuit current tolerance is a key indicator of switchgear. When a short circuit occurs, a huge current shock will be generated instantly, and the switchgear must be able to withstand it without damage. This requires that the switchgear should have sufficient strength and stability in design and manufacturing, from contact materials, arc extinguishing chamber structure to mechanical transmission components. For example, the contacts are made of arc-resistant alloy materials, the arc extinguishing chamber structure design can quickly guide and extinguish the arc, and the mechanical transmission components can still operate reliably under the strong electromagnetic force generated by the short-circuit current. Taking the common 10kV distribution cabinet as an example, the short-circuit current tolerance of its switchgear is generally required to be between 20kA and 31.5kA or even higher, and the specific value depends on the short-circuit capacity level of the power system.
Furthermore, when determining the selection of switchgear and the short-circuit current tolerance, the future development and expansion needs of the power system must also be considered. With the development of the enterprise or the increase in regional power load, the distribution system may face an increase in short-circuit current. Therefore, a certain margin should be reserved in the initial selection to avoid frequent replacement of equipment due to the short-circuit current exceeding the tolerance of the switchgear in the later stage, which increases costs and power outage risks. For example, when planning the power distribution system of a new industrial park, combined with the development plan of the park, the power load changes in the next 5-10 years are expected, and the switchgear with a short-circuit current tolerance slightly higher than the current demand is selected.
Finally, regular inspection and maintenance of the short-circuit current tolerance of the switchgear is an important part of ensuring the safe operation of the distribution cabinet. Through professional testing equipment and means, such as short-circuit tests and electrical parameter tests, problems such as contact wear and arc extinguishing performance degradation that may occur in the long-term operation of the switchgear can be discovered in time, and repaired or replaced. At the same time, a complete equipment archive is established to record the selection parameters, installation and commissioning conditions, operation and maintenance records of the switchgear, so that its short-circuit current tolerance and operating status can be quickly and accurately evaluated when needed, ensuring that the distribution cabinet is always in a reliable operating state and providing a solid guarantee for power supply.
