Plastic shell circuit breaker (plastic shell air insulated circuit breaker) is widely used in the low-voltage power distribution industry, used to cut off or isolate the normal and rated range of the fault current, to ensure the safety of lines and equipment. In addition, according to China’s “Construction Site Temporary Power Safety Technical Specification” requirements, the temporary power construction site power circuit breaker must be transparent shell, can clearly distinguish the main contact separation state, and the compliance circuit breaker must be affixed with the “AJ” mark issued by the relevant safety department.
QF to represent the circuit breaker, foreign drawings generally referred to as MCCB. Common plastic shell circuit breaker tripping and tripping methods are single magnetic tripping, hot magnetic tripping (double tripping), electronic tripping. Single magnetic tripping means that the circuit breaker only trips when the circuit has a short circuit fault. We usually use this switch in the heater loop or the motor loop with overload protection function. Thermal magnetic tripping is a line short circuit fault or the circuit current exceeds the rated current of the circuit breaker for a long time to trip, so it is also known as double tripping, often used in ordinary power distribution occasions. Electronic tripping is a mature technology emerging in recent years, with electronic tripping circuit breaker magnetic tripping current, hot tripping current, and tripping time are adjustable, more widely applicable occasions, but the cost of the circuit breaker is high. In addition to the above three types of tripping devices, there is a circuit breaker specially used for the motor circuit protection, its magnetic tripping current is generally above 10 times the rated current, to avoid the peak current when the motor starts, to ensure that the motor starts smoothly and the circuit breaker does not move.
Plastic shell circuit breaker has a variety of accessories can be hung, such as remote electric operation switch mechanism, excitation coil, auxiliary contact, alarm contact, etc.
When selecting the electric operating mechanism, pay attention should be paid to the supporting circuit breaker shell frame current, because the external size of different shell frame circuit breaker current and the torque of the closing mechanism are different.
When selecting the excitation coil, pay attention to the remote signal voltage level and AC and DC points. Personal advice when we do design, if the distant signal is 24V level, try not to use the remote voltage signal drive excitation coil, because excitation coil energy consumption, may bring pressure to the remote signal, if the trip point is more, remote equipment power is not enough to easily cause circuit breaker excitation coil voltage pressure drop, and cannot smooth buckle and has been electric burn excitation coil. At this time, we will use a small 24V intermediate relay for relay, select a 220V voltage level, and trip the local power for the excitation coil.
Auxiliary contacts are divided into single auxiliary and double auxiliary, and the samples are selected according to the actual demand quantity to save the design cost.
Most alarm contacts need external working power supply and confirmation during drawing and assembly.
The following picture is the domestic plastic shell circuit breaker attachment code, joint venture and imported brand attachment code is more disorderly do not list, you directly check the relevant brand samples.
In the design process, often meet the cabinet requires a fixed shell, but the load does not allow power failure without reason. Then we can use the plug-in circuit breaker, which circuit breaker fault directly unout can replace one, do not affect the other circuit continuous power supply.
Insert circuit breaker base in the body structure
Another important performance index of the plastic shell circuit breaker is its rated short circuit breaking ability, which directly affects the circuit breaker safety breaking fault current ability, generally 25 / 35 / 50 / 65 kh. In the actual selection process, we can choose according to the drawings requirements of the design institute, and we can calculate the expected maximum short circuit current value of the loop according to the experience. The breaker short circuit breaking capacity shall be greater than the expected maximum short circuit current of the circuit. In order to save costs, the short circuit breaking ability value is good enough.
Post time: Jul-19-2022
