Low-voltage switchgear adopts a modular design. Modularization is a form of standardization aimed at versatility. For withdrawable low-voltage switchgear, modular design is used in the structural design. Modular design means determining a basic module (e.g., E=20mm or 25mm), and the dimensions of the cabinet frame and its mounting holes, the space of functional unit areas, and the external dimensions of functional units (drawers or fixed mounting intervals) are all increased or decreased as needed in integer multiples of the basic module. For withdrawable low-voltage switchgear, the entire space adopts modular dimensions, and the external dimensions of functional units (drawers) are also designed modularly, so that each functional unit occupies a hexahedral space arranged according to modular combinations.
The working principle of low-voltage air circuit breakers (low-voltage circuit breakers) is to use the thermal expansion and bending of a bimetallic strip to trigger a lever, causing the circuit breaker to trip and providing overload protection. When a general overload occurs in the circuit, the overload current generates heat in the heating element, causing the bimetallic strip to bend and push the lever, disengaging the latch and breaking the main contacts to cut off the power. When a short circuit or severe overload occurs, the short-circuit current exceeds the instantaneous trip setting current value. The electromagnetic trip unit generates attraction, drawing the armature and striking the lever, causing the latch to rotate upwards around the pivot and disengage from the latch. The latch, under the action of the return spring, breaks the main contacts, cutting off the power. The tripping mechanism of the switch is a linkage device. When the main contacts are closed, they are locked in the closed position by the latch. If a fault occurs in the circuit, the relevant trip unit will activate, causing the latch in the tripping mechanism to disengage, and the main contacts will quickly break under the action of the release spring. There are three types of tripping methods: thermal, electromagnetic, and combined tripping.
"Air" in an air switch refers to the contacts opening and closing in air at atmospheric pressure. Its arc-extinguishing principle involves the negative resistance characteristics of DC arcs, the "zero-rest" phenomenon of AC arcs, the near-cathode effect, and methods such as grid arc extinguishing and magnetic blowout arc extinguishing.
The arc-extinguishing system is key to improving the breaking performance of circuit breakers. The new arc-extinguishing system uses a static arc-isolating cover and a dynamic arc-isolating cover with arc-isolating protrusions to provide insulation protection for the moving and stationary contact assemblies, reducing breakdown failures caused by arc overflow and improving arc-extinguishing capability.
Shenheng Power's patented low-voltage switchgear uses a duct unit and dual fans for coordinated heat dissipation, forming a multi-layer airflow distribution network and a three-dimensional heat dissipation field to solve the problem of uneven heat dissipation in traditional switchgear.