1. Basic Idea
The basic approach to electrical control cabinet design is based on logical thinking. A good design is one that conforms to logical control principles, ensures electrical safety, and meets production process requirements. However, to meet the manufacturing and usage requirements of electrical control equipment, a reasonable electrical control process design is essential. This design includes the structural design of the electrical control cabinet, its overall configuration diagram, the master wiring diagram, and the electrical assembly and wiring diagrams for each component. It also requires technical documentation such as component catalogs, input/output wire numbers, and a list of major materials.
2. Overall Configuration Design of Electrical Control Cabinet
The overall configuration design of the electrical control cabinet involves, based on the working principle and control requirements of the electrical schematic diagram, first dividing the control system into several components (all referred to as parts). Then, according to the complexity of the electrical control cabinet, each component is further divided into several sub-assemblies. Finally, based on the wiring relationships in the electrical schematic diagram, the input and output wire numbers for each part are determined, and the connection methods between them are adjusted. The overall configuration design is expressed in the form of a general assembly drawing and a general wiring diagram of the electrical system. These drawings should schematically show the location of the main components, the wiring relationships, the wiring methods, and the cable trays and conduits used.
The overall assembly drawing and wiring diagram of the electrical control cabinet (which can be separate or combined as needed) serve as the basis for sectional design and coordination of various parts into a complete system. The overall design should make the entire electrical control system centralized and compact. At the same time, where space permits, heat-generating components and electrical parts with high noise and vibration should be placed as far away from other components as possible or isolated. For large equipment with multiple workstations, the convenience of operation from two locations should also be considered. The main power switch and emergency stop control switch of the control cabinet should be placed in a convenient and obvious location.
The rationality of the overall configuration design is related to the manufacturing and assembly quality of the electrical control system, and will also affect the realization of the electrical control system's performance, its reliability, and the convenience and quality of operation, debugging, and maintenance.
2.1 Division of Electrical Control Cabinet Components
Because various electrical components are installed in different locations, a complete electrical control system must be divided into components. The principle for dividing components is:
(1) Group together components with similar functions;
(2) Minimize the number of connections between components, and place control electrical appliances with close wiring relationships in the same component;
(3) Separate the high-voltage and low-voltage controllers to reduce interference;
(4) To achieve a neat and aesthetically pleasing appearance, electrical appliances with similar dimensions and weights can be grouped together;
(5) To facilitate inspection and debugging of the electrical control system, components that require frequent adjustment, maintenance and are easily damaged are grouped together.
2.2 When dividing the electrical control cabinet into components, the wiring methods between components, between electrical boxes, and between electrical boxes and the controlled devices must be addressed. The wiring methods between the various parts and components of the electrical control cabinet should generally follow these principles:
(1) The incoming and outgoing lines of switchgear and control board are generally connected by terminal blocks or lugs. Different specifications of terminal blocks or lugs can be selected according to the current and the number of incoming and outgoing lines.
(2) Electrical cabinets, control cabinets, cabinets (units) are connected to each other and to the controlled equipment by terminal blocks or industrial connectors;
(3) Various types of standard connectors should be used to connect the low-voltage control components and printed circuit board components.
(4) The connection between components in electrical cabinets, control cabinets, and cabinets (tables) can be made by directly connecting the components themselves using their own terminals; the transition connection should be made by using terminal blocks, and the ends should be treated with terminals of the appropriate specifications.
3. Design and drawing of electrical component layout diagrams
An electrical component layout diagram is a combination of certain electrical components according to specific principles. The design of an electrical component layout diagram is based on component schematics, assembly divisions, etc. The following principles should be followed during the design process:
(1) When arranging electrical components in the same component, attention should be paid to installing large and heavy electrical components under the electrical board, while heating components should be installed at the top or rear of the electrical control cabinet. However, thermal relays should be placed at the bottom because the output terminal of the thermal relay is directly connected to the motor for easy wiring, while its input terminal is directly connected to the contactor for easy wiring and the shortest possible wiring, and is also conducive to heat dissipation.
(2) Strong and weak currents should be separated and shielded to prevent external interference.
(3) Electrical components that require frequent maintenance, repair and adjustment should not be installed too high or too low. The installation positions of manually operated switches and instruments that require frequent monitoring should conform to ergonomic principles.
(4) The arrangement of electrical components should take into account safety clearances and be neat, beautiful and symmetrical. Electrical components with similar size and structure can be placed together to facilitate processing, installation and wiring. If a cable tray wiring method is used, the spacing between each row of electrical components should be appropriately increased to facilitate wiring and maintenance.
(5) Once the positions of each electrical component are determined, the electrical layout diagram can be drawn. The electrical layout diagram is drawn based on the outline of the electrical components, that is, using their axes as a reference, and marking the spacing dimensions of each component. The installation dimensions and tolerance range of each electrical component should be marked according to the product manual to ensure the processing quality of the mounting plate and the smooth installation of each electrical component. Electrical components in large electrical cabinets should preferably be installed between two mounting beams. This can reduce the weight of the cabinet, save materials, and facilitate installation. Therefore, the longitudinal installation dimensions should be calculated during the design.
(6) In the design of electrical layout diagram, the number of incoming and outgoing lines of this component, the specifications of the wires used and the location of the outgoing lines, the incoming and outgoing lines should be selected, and the terminal blocks, connectors or plugs should be marked in a certain order.
4. Drawing wiring diagrams for electrical components
Electrical component wiring diagrams are drawn based on the electrical principles of the components and the layout of electrical elements. They represent the connection relationships of the complete set of equipment and serve as the basis for electrical installation, maintenance, and wiring troubleshooting. Wiring diagrams should be drawn according to the following principles:
(1) The drawing of the wiring diagram and phase wiring table shall comply with the provisions of GB6988.6-1993 "Drawing of Functional Table Diagrams of Control Systems";
(2) All electrical components and their leads shall be marked with text symbols and wiring numbers consistent with those in the electrical schematic diagram. The compilation of item codes, terminal numbers and wire numbers in the schematic diagram shall comply with the provisions of GB5094-1985 "Item Codes in Electrical Technology", GB4026-1992 "General Rules for Identification and Application of Alphanumeric Systems for Terminals and Specific Wire Ends of Electrical Equipment" and GB4884-1985 "Marking of Insulated Wires", etc.
(3) Unlike electrical schematic diagrams, in wiring diagrams, all parts (contacts, coils, etc.) of the same electrical component must be drawn together;
(4) All electrical wiring diagrams shall be drawn with fine lines. There are two types of wiring methods: front wiring and back wiring. Front wiring is generally used. For simple electrical control components with a small number of electrical components and simple wiring relationships, the connections between components can be drawn directly. For complex components with a large number of electrical components and complex wiring, wiring channels are generally used. As long as the wiring number is marked on each electrical component, it is not necessary to draw the connections between components.
(5) The wiring diagram should indicate the type, specifications, cross-sectional area and color requirements of all wires used for wiring;
(6) When connecting components to external circuits, large cross-section wires should be connected by connectors, while others should be connected via terminals.
5. Design of electrical control cabinet and non-standard parts drawings
Electrical control devices typically require separate electrical control cabinets or boxes, and their design needs to consider the following aspects:
(1) Determine the overall size and structural type of electrical boxes and cabinets according to the operational needs and the dimensions of various electrical components in the control panel, box, and cabinet. Under normal circumstances, the overall size of the electrical control cabinet should conform to the basic structural dimensions and series.
(2) Based on the overall dimensions, structural type, and installation dimensions of the electrical control cabinet, design the mounting bracket inside the cabinet, and mark the dimensions of the mounting holes, mounting bolts, and grounding bolts, while also indicating the connection method. The materials for the cabinet and box should generally be special profiles for cabinets and boxes;
(3) Design the opening method and type of the electrical control cabinet according to the requirements of on-site installation location, operation and maintenance convenience;
(4) To facilitate ventilation and heat dissipation of electrical appliances inside the control cabinet, ventilation holes or ventilation slots should be designed in appropriate parts of the cabinet. If necessary, forced ventilation devices and ventilation holes should be designed in the upper part of the cabinet.
(5) To facilitate the transportation of electrical control cabinets, suitable lifting hooks should be designed or movable wheels should be designed at the bottom of the cabinet.
In summary, based on the above requirements, a rough sketch of the electrical control cabinet's exterior should be drawn first, estimating the dimensions of each part. Then, a scaled-down outline drawing should be created, further adjusting the proportions of each dimension considering symmetry, aesthetics, and ease of use. After the exterior of the electrical control cabinet is finalized, the structural design of each part of the control cabinet should be carried out according to the above requirements. This includes drawing the overall assembly drawing of the cabinet and drawings of each door, control panel, base plate, mounting bracket, decorative strip, and other components, noting the processing requirements. Appropriate door locks should then be selected for the electrical control cabinet as needed. Of course, electrical cabinets vary in shape and structure, and the advantages of various types should be incorporated into the cabinet design. For non-standard electrical installation parts, part drawings should be created according to the mechanical part design requirements. Tolerance requirements should be noted for all mating dimensions, and processing requirements should be explained.
Finally, based on various drawings, a comprehensive statistical analysis of all parts and materials required for the electrical control cabinet should be conducted, and a summary list of purchased finished parts, a list of standard parts, a list of main material consumption quotas, and a list of auxiliary material quotas should be compiled by category. This will enable purchasing personnel and production management departments to prepare materials according to equipment manufacturing needs, make good production preparations, and facilitate cost accounting.
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