Design Step-by-Step Guide for Power Distribution Panels

The power distribution panel is a power distribution equipment used to receive and distribute electric energy and to control, protect and measure the distribution lines. Common power distribution panels are divided into DC and AC.

1. Requirements for power distribution panel

The technical requirements and installation requirements for the power distribution panel are as follows.

1.1 The left door panel in the power distribution panel should have the primary system diagram of the panel, the instrument wiring diagram, the control circuit wiring diagram and the corresponding terminal number diagram; the right door panel in the power distribution panel should have a list of electrical components installed in the panel, The manufacturer, model, specification, etc. should be indicated in the table.

1.2 Each electrical appliance, instrument, terminal block, etc. of the power distribution panel shall be marked with serial number, name, route (or purpose) and operating position.

1.3 The current circuit wiring of the secondary circuit in the power distribution panel shall adopt copper core insulated wires with a cross-section not less than 2.5mm2 and a voltage not lower than 500V, and the cross-section of other circuit wiring shall not be less than 1.5mm2. The wiring should be neat and beautiful, with good insulation and no joints.

1.4 The low-voltage electrical appliances installed in the power distribution panel should be arranged neatly and have the same phase sequence.

1.5 The control switch should be installed vertically, with the upper end connected to the power supply and the lower end connected to the load. The distance between the center of the operating handle of the switch and the ground is generally 1.2-1.5m; the distance between the handle for side operation and buildings or other equipment should not be less than 0.2m.

1.6 The switch controlling two independent power sources should be equipped with reliable mechanical and electrical locking devices.

1.7 The power distribution panel should be firmly installed on the foundation steel. The top of the section steel should be 10mm above the ground. The connection between the equipment in the screen and each component should be firm.

2. Design steps of power distribution panel

The design of the power distribution panel is generally carried out according to the following steps:

2.1 Determine the control and protection scheme for the outgoing line of the power distribution panel
First of all, we must find out the electricity consumption situation in the power distribution area. According to the load distribution and the short-term development plan, determine the power supply methods such as three-phase three-wire or three-phase four-wire.

After each outgoing line is determined, the control and protection scheme of each outgoing line can be determined according to the size of the load carried by each outgoing line, the length of the line, and the requirements for power supply reliability. Generally, shunt isolating switches and shunt automatic switches are installed; for shunts with short lines and small loads, load switches (switches with arc extinguishers) and fuses can be used for shunt control and protection.

2.2 Determine the control and protection scheme of the power distribution panel incoming line
After the outgoing lines of the power distribution panel and their control and protection schemes are determined, the incoming lines of the power distribution panel and their control and protection can be determined according to the number of outgoing lines, the control and protection methods of each outgoing line, and the capacity of the distribution transformer. Program.

When there are many shunts and the capacity of the transformer is large, the main isolating switch and the main automatic switch should be installed; when there are few shunts and the capacity of the transformer is small, the isolating switch and fuse can be used as the main switch and the main protection.

When the capacity of the distribution transformer is small, the low-voltage line is short, the shunt is small, and the leakage switch protection is not installed, the main automatic switch with or with leakage protection should be installed.

3. Installation of power distribution panel

3.1 Screen surface of power distribution panel: The screen surface of power distribution panel should be smooth and painted, and the frame should be firm. The equipment on the screen should be arranged reasonably, and the wiring should be neat and beautiful. Meters and indicator lights should be installed on the upper part of the switchboard to facilitate monitoring and avoid damage; switches should be set in the middle for easy operation; heavier electrical equipment should be set in the lower part to stabilize the switchboard; other equipment should be placed in short wiring. The bare aluminum bus bars fixed on the top of the distribution screen should be painted with yellow, green, red, black and other colors as phase separation signs, and the distance between each device should meet the safety requirements.

3.2 Wires: The length of the lead-in wires and lead-out wires of the power distribution panel should have an appropriate margin for maintenance. The secondary circuit should use insulated wire, the cross-sectional area: copper wire not less than 1.5mm2, aluminum wire not less than 2.5mm2. The wiring layout should be horizontal and vertical, neat and beautiful. When the wiring passes through the wooden plate, it should be sleeved, and when it passes through the iron plate, it should be covered with a rubber retainer to maintain good insulation.

3.3 Switch: The switch should be installed vertically. The upper end of the switch is connected to the power supply, and the lower end is connected to the load. The connection must not be reversed, and the phase sequence should be consistent. Each branch should be marked with the name of the branch line. The movable part of the AC contactor and the blade of the knife switch shall not be charged.

3.4 Grounding of the power distribution panel: the screen surface of the power distribution panel, the metal shell and metal frame of the electrical appliances on the power distribution panel, etc., should be protected and grounded, and the grounding resistance should not be greater than 4n. The zero line in the neutral point direct grounding system should be repeatedly grounded at the lead-in line to achieve reliable protective zero connection.

3.5 Installation of power distribution panel: The installation height of the power distribution panel should be appropriate. Generally, the meters and indicators are 1.5-2m away from the ground. The power distribution screen is installed on the wall, and the bottom of the screen is about 1.2m away from the ground. The power distribution screen is installed on a vertical iron frame, and the top of the screen is about 2.1m away from the ground. The installation location is based on the principles of safety, convenience for observation and maintenance.

3.6 Requirements for the distribution box: The requirements for the distribution box are the same as those for the switchboard. In addition, the distribution box should have a door, and the size of the door depends on the size of the distribution box. If the box is wider, the doors can be opened in pairs. The wooden distribution box can be covered with iron sheets before and after the plate as needed to prevent electric fire. Outdoor distribution boxes should have rainproof facilities.

4. Management system of power distribution panel

4.1 Unrelated personnel are not allowed to enter the power distribution panel room, and other items are not allowed to be stored in the room.

4.2 Operators of power distribution panels must understand and master power distribution management, safe operation knowledge and maintenance techniques.

4.3 The power distribution screen should be wiped frequently to keep it clean.

4.4 Fire-fighting equipment should be provided near the distribution panel and distribution box, and should be maintained to prevent failure.

4.5 Insulation rubber sheets should be laid around the power distribution screen, and grids should be installed on the power distribution screen.

4.6 When inspecting, especially when overhauling, there should be a sign saying "overhauling, do not close the switch" to prevent accidents.

4.7 The components of the power distribution panel shall not be disassembled at will. If the wiring is to be changed, it must be approved by the person in charge of the equipment group.