Author: Site Editor Publish Time: 2022-10-20 Origin: Site
The circuit breaker, whose function is to protect circuits from damage caused by overcurrent, overload, leakage or short circuit, is an automatically operated electrical switch design. Its basic function is to interrupt the current after the protection mechanism detects a fault. Unlike fuses, which must be replaced after one operation, circuit breakers can be reset (manually or automatically) to restore normal operation.
·Rated ultimate short-circuit breaking capacity Icu
There are two types of breaking capacity indicators for circuit breakers: rated limit short-circuit breaking capacity Icu and rated operating short-circuit breaking capacity Ics. Ics as a characteristic parameter is not simply a consideration of the breaking capacity of the circuit breaker, but as a breaking indicator, i.e. after breaking several short-circuit faults, it can still guarantee its normal operation. For molded-case circuit breakers, there should be sufficient Icu to break the short-circuit current so that the switch trips. According to the provisions of the plastic case circuit breaker Ics as long as greater than 25% Icu even if qualified. And most of the current market circuit breakers Ics in (50%-75%) Icu between, so the power supply requirements are not high power distribution system, only Icu must be considered.
·Current limiting breaking capacity
When a short circuit occurs in a circuit breaker, the contacts open quickly to produce an arc, which is equivalent to a rapidly increasing arc resistance in the line, thus limiting the increase in fault current. The less the circuit breaker breaks, the closer the Ics is to the Icu, the better the current limiting effect, which also greatly reduces the electromagnetic, electric and thermal effects caused by the short-circuit current on the circuit breaker and the electrical equipment and prolongs the service life of the circuit breaker.
Short-circuit protection is a short-circuit instantaneous tripping. Attention should be paid to timely adjustment of the protection after the change of load, to prevent the setting value is too small frequent tripping affect the quality of power supply, or the setting value is too ambassador line and equipment can not be effectively protected.
·Overload delay protection
Overload delay protection refers to the danger of burning equipment when the load current exceeds the limit of the equipment, and the protection device can cut off the power within a certain time. Overload has a process of heat accumulation, the protection action does not need to be too fast. For short-term overcurrents, the protection should not operate.
The isolation function is the requirement that the leakage current after the circuit breaker has been disconnected does not cause harm to persons and equipment. After multiple short circuit trips the switch performance decreases and the leakage current increases. A leakage current of less than 30mA is safe for the human body, while a leakage current of more than 300mA for more than 2 hours in a harsh environment may damage the insulation and cause a phase to phase short circuit and thus a fire.
There are 2 types of leakage protectors: thermal magnetic and electronic. In comparison, electronic leakage protectors have the advantages of small size, high accuracy and high sensitivity, but their anti-interference ability is poor. When the leakage current reaches the set value, the execution circuit receives the induced voltage signal from the secondary side of the zero-sequence current transformer and drives the changeover contact to output a leakage protection signal, which causes the decoupler to act to cut off the power supply.
The leakage current of the general terminal switch is 30mA, and that of the upper branch switch is 300mA. arcing short circuits with a high risk of fire are difficult to cut off effectively by short circuit protection, while leakage protectors can reliably disconnect earth faults to prevent personal electrocution and phase short circuit faults.