What Is Overload Protection?

Overload protection is an overload protection device that prevents the main power line from being overheated and damaged due to overload.

Electrical circuits that allow continuous passage without overheating the wires

The main reasons for the overload are improper selection of the cross section of the wire, and the actual load has exceeded the safe current of the wire;

There is also the phenomenon of "small horse-drawn cart", that is, too many high-power devices are connected to the line, which exceeds the load capacity of the power distribution line.

When lighting circuits in important material warehouses, residential places and public buildings, power lines that may cause long-term overload of conductors or cables, and insulated conductors with ductile sheaths are laid on combustible or refractory building components , Should take overload protection. The circuit's overload protection should use automatic switching. During operation, the setting current of the long delay action of the automatic switch should not be greater than the long-term allowable load current of the line. If used

The amount of current in an electrical circuit that is allowed to pass continuously without overheating the wire is called the safe current carrying capacity or safe current. When the load is too large, the current flowing through the wire will exceed the safe ampacity, which is the wire overload. The overload of the wire will cause the temperature of the wire to rise. Generally, the maximum allowable working temperature of the wire is 65 ° C. When the wire is overloaded, the temperature of the wire exceeds the maximum allowable working temperature, which will cause the wire insulation to age quickly and even cause a fire due to the burning of the line. Therefore, in the actual power supply line, we usually have the function of overload protection equipment to prevent the safety hazard caused by the overload of the load ^[2]

In the field of communication power, air switches and fuses are usually used to achieve overload protection. An air switch or fuse can be placed in the power supply line to achieve overload protection. These two devices are implemented differently:

Air switch: When the current flowing through the air switch is greater than its rated current, the air switch will automatically trip. The air switch is a re-use device. It can be reused after it is closed after tripping.

Fuse: When the current flowing through the fuse is greater than its rated current, the fuse will open. The fuse is a one-time device and cannot be used after being fused.

The speed of the motor is changed by changing the connection of the windings, that is, by changing the number of pole pairs of the rotating magnetic field of the motor to change its speed.

The two-speed motor (fan) usually has a low speed, and sometimes the fan rotates at a high speed, which is mainly achieved by changing the winding connection method of the motor coil through the following external control circuit switching.

1. Two common windings with different pairs of poles are embedded in the stator slot, and the connection of the stator windings of the motor is changed by switching the external control circuit to change the number of pairs of magnetic poles;

2. Two independent windings with different pole pairs are embedded in the stator slot;

3. Two independent windings with different pole pairs are embedded in the stator slot, and each winding can have a different connection ^[3] .