Low-voltage electrical appliances, its full name is low-voltage switchgear, and its essence belongs to the switch-type components.
We have seen the power grid which is closely related to our life, it consists of power plants, step-up substations, towers and overhead lines for transmitting electricity, step-down substations, main transformers and medium voltage switchgear, main transformers for medium voltage to low voltage, low voltage switchgear, etc., while our electric loads are located at the very end.
Let’s look at the circuit diagram in Figure 1: the leftmost part of the circuit diagram is a 10kV/400V transformer with an angle connection on the MV side and a star connection on the LV side. The low-voltage side has the main incoming switch K1, the system bus, and feeder switches K2 to K5, as well as the power-using load.
The power-using loads in the diagram are represented by R1 to R18. Don’t think they are resistors, they can be microwave ovens, refrigerators, or motors and lighting circuits.
Note: We see that the low voltage side of the transformer is fed at one point, but after distributing the power through the system bus, and then through each feeder switch, the power is distributed to multiple points.
This is called the point-to-multipoint structure of power distribution.
From this we know that the task of the system bus in the original distribution cabinet is to distribute electrical energy, the task of the main incoming switch is to control the total incoming end of electrical energy and line protection, while the task of the feeder switch is to control the feeder circuit and line protection.
Knowing the tasks of the switchgear, what necessary functions should the switchgear have?
These functions include
1. the ability to carry operating currents at rated voltages
2. the ability to carry overload currents and, for a certain period of time, the impact of short-circuit currents
3. to cut off the fault current, to achieve line protection.
These three functions involve theoretical knowledge and technical knowledge is extremely rich. Once you understand these three functions and the corresponding technical parameters of low-voltage electrical appliances, you will also understand the application overview and configuration points of low-voltage switchgear.