Learn About the Air Switch (2)
3. Mechanical principle of air switch
(1) The air switch is a circuit breaker, which is used for making, breaking, and carrying rated working currently in the circuit, and can perform reliable protection in the case of overload, short circuit, and under-voltage of the line and motor. The dynamic and static contacts and contact rods of the circuit breaker are designed to be parallel, and the dynamic and static contacts are disconnected by the electric repulsion generated by the short circuit, with high breaking capacity and strong current limiting characteristics. When short-circuited, the aromatic insulators around the static contacts are vaporized to cool and extinguish the arc, and the arcing distance is zero. The arc extinguishing chamber of the circuit breaker adopts a metal grid structure, and the contact system has a repulsive force current limiting mechanism. Therefore, the circuit breaker has a high breaking capacity and current limiting capacity. The circuit breaker can be divided into three types according to the tripping method: thermal, electromagnetic, and compound tripping.
(2) When the line is short-circuited or severely overloaded, the short-circuit current exceeds the instantaneous trip setting current value. The electromagnetic release generates enough suction, attracts the armature, and hits the lever so that the hook rotates up around the shaft seat and releases the lock. Under the action of the reaction force spring, the lock will disconnect the three pairs of main contacts and cut off the power supply.
(3) When the line is generally overloaded, although the overload current cannot make the electromagnetic release actuate, it can make the thermal element generate a certain amount of heat, which will cause the bimetallic sheet to be heated and bend upward and push the lever to disengage the hook and the lock. The main contact is disconnected, and the power is cut off.
(4) Air switch arc extinguishing device
The main contacts are closed by an operating mechanism (manual or electric). Its contact system can not only connect or cut off the normal working current because it is equipped with an arc extinguishing device. It can also quickly cut off the fault current several times larger than the normal working current when a fault occurs, so as to effectively protect the electrical equipment in the circuit. The tripping mechanism of the circuit breaker is a set of linkages.
(5) Air switch tripping mechanism
When the main contact is closed by the operating mechanism, it is locked in the closed position by the lock hook. If a fault occurs in the circuit, the associated release will act to disengage the latch in the release mechanism. Then the main contact is quickly disconnected under the action of the released spring. According to the different protection functions, the release can be divided into overcurrent release and voltage loss release.
a. Under normal circumstances, the armature of the overcurrent release is released. In the event of a serious overload or short-circuit fault, the coil connected in series with the main circuit will generate a strong electromagnetic suction to attract the armature downward and open the lock hook to disconnect the main contact.
b. The work of the Undervoltage release is just the opposite. When the voltage is normal, the electromagnetic suction attracts the armature, and the main contact is closed. In the event of a severe drop in voltage or a power outage, the armature is released to open the main contacts. When the power supply voltage returns to normal, it must be re-closed before it can work, which realizes the voltage loss protection.
4. The basics of the air switch
a. According to the number of poles: unipolar, bipolar, and tripolar.
b. According to the protection form: electromagnetic release type, thermal release type, compound release type (commonly used), and non-release type.
c. According to the full breaking time: general and fast (acting before the tripping mechanism, the tripping time is within 0.02 seconds).
d. According to the structure type: plastic case type, frame type, current limiting type, DC fast type, demagnetization type, and leakage protection type.
