The low-voltage power distribution system consists of a distribution substation (usually reducing the transmission voltage of the power grid to the distribution voltage), a high-voltage distribution line (i.e., a voltage above 1 kV), a distribution transformer, a low-voltage distribution line (a voltage below 1 kV), and corresponding control and protection equipment.
Generally includes:
Main equipment such as incoming line cabinet, capacitor compensation cabinet, contact cabinet, and outgoing line cabinet.
Low-voltage cabinet transformer section:
Transformer → incoming line cabinet → reactive compensation cabinet → busbar cabinet → outgoing line cabinet.
Main equipment of low-voltage power distribution system
Ⅰ. Low-voltage incoming line cabinet
1. Incoming line cabinet is a switch cabinet that introduces power from the outside. Generally, a 10kV power supply is introduced from the power supply network. The 10kV power supply sends the power to the 10kV busbar through the switch cabinet. This switch cabinet is the incoming line cabinet.
Ⅱ. Outgoing line cabinet
The outgoing line cabinet is a switch cabinet that distributes power from the busbar.
1. From the 10kV busbar to the power transformer through the switch cabinet, this switch cabinet is one of the 10kV outgoing cabinets. Install the export switch cabinet on the low-voltage side of the transformer to send the electric energy to the low-voltage busbar through this switch cabinet, and then install several low-voltage switch cabinets on the low-voltage side to send the electric energy to various power users. These low-voltage switch cabinets are all outgoing cabinets.
For substations with voltage levels of 35-110kV and above, the incoming cabinet refers to the transformer low-voltage (10kV) switch cabinet. That is, the first cabinet connected from the low-voltage side output of the transformer to the initial end of the 10kV busbar: called the incoming cabinet, also known as the low-voltage incoming cabinet.
2. The incoming cabinet is the main switch cabinet on the load side. The cabinet is responsible for the current carried by the entire busbar. Since the switch cabinet is connected to the main transformer and the low-voltage side load output, its role is important. In terms of relay protection, when the busbar or circuit breaker on the low-voltage side of the main transformer fails, the overcurrent protection on the low-voltage side of the transformer must be used to trip the incoming switch to clear the fault.
When the busbar on the low-voltage side fails, the backup protection on the low-voltage side of the main transformer must be used to clear the incoming switch. The transformer differential protection also clears the circuit breaker on the low-voltage side of the transformer, i.e. the incoming switch.
3. It plays the role of isolating, disconnecting, protecting, monitoring, and controlling the power supply quality and safety of the main circuit.
The function of the capacitor compensation cabinet is to balance the inductive load of the equipment and improve the power factor to improve the utilization rate of the equipment. In order to improve the energy waste caused by the low power factor of the power grid and these factors that are unfavorable to the power supply generation, the power factor of the power grid must be effectively improved. But it is obviously unreasonable and usually impossible for all these reactive powers to be provided by generators and transmitted over long distances. The reasonable way is to generate reactive power where reactive power is needed, that is, to increase reactive power compensation equipment and devices. That is, capacitor compensation cabinet.
