The current quick-break protection, as the name implies, refers to the current protection of the instantaneous action when the cable joint current changes or exceeds the preset protection value range. Written as: the current protection for the instantaneous short-circuit current amplitude increase is called current fast-break protection. In order to ensure the selectivity of the microcomputer protection device, it can only protect one way of the line. It is assumed that the current is installed on the line every day. Quick-break protection, when a fault occurs on the line, it is hoped that the protection can act instantaneously. His protection range is preferably 100% of the length of the line. However, whether this desire can be achieved requires detailed analysis.
    In order to solve this contradiction, there are two ways, usually the priority is to ensure the selectivity of the action, that is, to ensure that the next line exit is not activated when the protection device startup parameter is set. In the microcomputer protection technology, this is also called To avoid the short-circuit condition setting at the exit of the next line, another method is to use an automatic reclosing to correct this non-selective action in the individual case when the quick-cut fault is the primary condition.
When the electrical equipment in the power grid fails, the short-circuit current is very large. According to the basic operating principle of the relay, if the short-circuit current is determined as the operating current of the relay by calculation in advance, the faulty device can be protected. Overcurrent protection and current quick-break protection are based on this principle. In order to ensure the selectivity of the action, according to the characteristics of the short-circuit current (the closer the fault point is to the power supply, the larger the short-circuit current), the overcurrent protection has an action time limit, and the current quick-break protection has no action time limit, that is, when a short circuit occurs. When it immediately moves to cut off the fault, it has no time limit characteristics and is often used in conjunction with overcurrent protection.
     The quick-break protection cannot protect the full length of the line, only selectively protects part of the line, and the remaining part is the dead zone of quick-break protection. In order to avoid the above situation, the quick-break protection can also be made into a slight time limit, which is called time-limited current quick-break protection. It cooperates with the untimed current to eliminate the action dead zone of the current quick-break protection.