What Is Breaking Capacity?

The breaking capacity refers to a special function of the circuit breaker switch. At present, there are 36KA, 50KA and other specifications. The breaking capacity of a circuit breaker refers to the ability of the circuit breaker to safely cut off the fault current (often also the determining factor of the price), and it is not necessarily related to its rated current. Generally divided into limit breaking capacity Icu and running breaking capacity Ics (many micro-breaks are not distinguished). The breaking capacity of domestic small circuit breaker products is mostly in the range of 4.5 ~ 6kA, and the reliability of the breaking capacity is not high, which restricts the development of small circuit breakers.

Breaking capacity refers to a special type of circuit breaker switch

The rated short-circuit breaking capacity (Ics) is the short-circuit current that can be switched on and off after a certain test procedure under certain test parameters (voltage, short-circuit current and power factor). Continue to carry the breaking capacity of its rated current, and its test procedure is O-t (online) CO-t (online) CO. Short-time withstand current (Icw) refers to the ability to withstand 0.05, 0.1, 0.25, 0.5, or 1s and the circuit breaker does not allow tripping under a certain voltage, short-circuit current, and power factor. When buckling, the evaluation index of the electric and thermal stability of the circuit breaker is for class B circuit breakers. Generally, the minimum value of Icw is: when In2500A, it is 12In or 5kA, and In> 2500A At the time, it is 30kA (Icw of DW45_2000 is 400V, 50kA, Icw of DW45_3200 is 400V, 65kA). The test conditions for the short-circuit breaking capacity of the operation are extremely harsh (one-time breaking, two-time breaking). Since it continues to carry the rated current after the test (the number of times is 5% of the life), it does not only need to verify the tripping characteristics, Frequency withstand voltage, but also to verify

An important principle for selecting a circuit breaker is the short-circuit breaking capacity of the circuit breaker

In the current situation, miniature circuit breakers are moving towards a trend of high breaking capacity, small size and modularization. The breaking capacity of domestic small circuit breaker products is mostly in the range of 4.5 ~ 6kA, and the reliability of the breaking capacity is not high, which restricts the development of small circuit breakers. How to improve the breaking capacity and reliability of the small circuit breaker by optimizing and improving the related structure while maintaining the existing production process and technology remains the focus of attention. Therefore, we can consider how to improve the breaking performance through process improvement based on the arc generation mechanism. Mechanism. During the breaking process of small circuit breakers, the contact area of the dynamic and static contacts gradually decreases. The increase in contact resistance and current density leads to an increase in temperature. The dynamic and static contacts are melted under high temperature heating to form a liquid metal bridge. With the separation of the dynamic and static contacts, the temperature of the liquid metal bridge continues to increase until it is broken and vaporized to form metal vapor. At this time, the metal vapor released between the dynamic and static contacts creates a thermal ionization condition. Collisions between electrons and ions will produce ionization, and atom-to-atom collisions and thermal radiation will also produce ionization. When the applied power is higher than the arc starting voltage, the molten liquid metal bridge will generate an arc. Quickly extinguishing the arc is an important technical indicator to improve the breaking performance of small circuit breakers. The breaking performance of small circuit breakers is discussed from the following aspects. The mechanism of arc generation Small circuit breakers may generate arcs when they are closed and opened. However, in order to meet the needs of practical applications, in most cases we only focus on and study the small circuit breakers generate arcs when they open the circuit.

Since the 20th century, people have experienced the understanding from magnetic blowout arcs to gas blowout arcs, and have studied more deeply the ways to increase the driving force of arc motion. By designing a reasonable vent hole size to ensure the pressure difference between the inside and outside of the arc extinguishing grid, it can also drive the arc movement and cool the arc, and reduce the stagnation time of the arc, so as to effectively break the arc. The reduction in the area of the air vent is beneficial to arc blowing, but the excessive pressure of the arc extinguishing chamber causes the shell to burst. In addition, it has been proved in practice that excessively reducing the area of the vent holes will cause a back breakdown phenomenon of the arc, so the cross-sectional area of the vent holes can be appropriately increased, and the rapid extinguishment of the arc can be promoted through cooperation with the buffer zone. ^[3]