First, low-voltage electrical appliances refer to electrical appliances with a rated voltage of 1000V or less. Low-voltage electrical appliances are widely used and have a wide variety of products. There are various types of product structures, which are generally divided into: knife switches, fuses, automatic switches, controllers, contactors, controllers, control relays, rheostats, voltage regulators, etc. Low-voltage electrical appliances can be divided into: low-voltage control appliances for power transmission systems, such as relays, contactors, electromagnets, varistors, controllers, master controllers, etc.; for low-voltage distribution systems Low-voltage power distribution equipment, such as: knife switch, air switch, fuse breaker, etc. The following describes the functions and features of several accessories: First, the knife switch The application of the knife switch is mainly based on the rated current of the power circuit, and this current should be equal to the sum of the negative current ratings of the branches controlled. If there is a motor in the circuit, it should be calculated according to the motor and starting current. In addition, it should be selected according to the short-circuit current that may occur in the circuit. Its model is expressed as: the knife switch is used for AC voltage below 500V, DC electric circuit below 440V, used to cut off the electrical appliances. Its maximum rated current is up to 1500A. The knife switch has no overcurrent protection. It should be used in series with appliances with overcurrent protection devices, such as fuses, automatic switches, etc. The knife switch has poor arc-extinguishing ability. Generally, the knife switch without the arc-extinguishing cover is not used to cut off the load current. Although the knife switch with the arc-extinguishing grid cover can cut off the rated load current, it is generally only used for isolation. Source: Transmission and Distribution Equipment Network Second, the fuse The rated current of the fuse is different from the rated current of the melt. In a fuse of a rated current class, several melts of different rated current levels are charged. Therefore, when selecting a fuse for the protection of lines and equipment, it is first necessary to clearly select the specifications of the melt, and then select the fuse according to the melt. Selection principle: 1. The protective characteristics of the fuse must be well matched to the overload characteristics of the protected object, so that it provides reliable protection over the entire curve range. 2. The limit breaking current of the fuse should be greater than or equal to the effective value of the short-circuit surge current that may occur in the protection circuit, otherwise reliable short-circuit protection cannot be obtained. 3. The limit breaking current of the fuse should be greater than or equal to the effective value of the short-circuit surge current that may occur in the protection circuit, otherwise reliable short-circuit protection cannot be obtained. Third, the AC contactor The use and structural characteristics of AC contactors and common fault AC contactors are widely used in electric drive systems. As a control device for frequent or disconnected load circuits, AC contactors are electrically operated, so they are suitable for remote operation and automatic control systems. . AC contactors do not have overcurrent protection, so use in the line needs to be used with appliances with overcurrent protection. Such as matching fuses, e-moving air circuit breakers, thermal relays, etc. The AC contactor consists of an electromagnetic system, a contact system, an arc extinguishing device, and a mechanism attachment. The electromagnetic system includes an electromagnetic coil and a static and dynamic iron core. The static iron core is on the lower and moving iron cores, and the electromagnetic coil is on the static iron core. Please visit: Transmission and Distribution Equipment Network for more information When the electromagnetic coil is energized, the static and moving iron cores are sucked. The contact system includes a set of three-phase main contacts and two normally open, two normally closed auxiliary contacts. The main contact and the moving iron core are connected together. The main contact is a double break and is used to turn on the main circuit. The auxiliary contacts are connected in the control loop to achieve various control methods. The arc extinguishing device is generally a grid arc extinguishing cover made of ceramics for extinguishing an arc generated by breaking a large current in time. The structure is used to support and fix the working parts and to function as electrical insulation. When the main circuit needs to be turned on, the electromagnetic coil of the AC contactor is first turned on. When the electromagnetic coil is energized, a magnetic force is generated to pull the moving iron core, and the moving contact connected to the moving iron core is connected to the circuit. When the electromagnetic coil is de-energized, the suction force disappears, the moving iron core is separated by the force of the spring, and the contact cuts off the circuit. This feature forms the voltage loss protection function of the AC contactor. Fourth, automatic air circuit breaker The main use of automatic air circuit breakers Automatic air circuit breakers are a major type of low voltage switchgear. Also commonly referred to as automatic air switches, automatic switches, and the like. Because of its good operating characteristics, the closing operation speed is fast: protection characteristics - with overload, short circuit, voltage loss and other protection performance: arc extinguishing characteristics - there is a deionization grid arc extinguishing chamber can quickly extinguish the arc. Because it combines the good function of circuit breakers and protection devices, it is very convenient to use, so it is used as a control and protection device in low-voltage power distribution systems. Concerned about surprises Label: Classification of low-voltage electrical appliances and the functions and features of each accessory Previous: Inner-flip hardware installation and principle Next: Precautions for the use of fire-proof mud
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