I. Basic Ideas
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, wiring diagram, and electrical assembly and wiring diagrams for each component. It also requires technical documentation such as component catalogs, wire numbers, and a list of major materials.
II. Overall Configuration Design of Electrical Control Cabinet
The overall configuration design task of the electrical control cabinet is to first divide the control system into several components (all of which are called parts) based on the working principle and control requirements of the electrical schematic diagram. Then, according to the complexity of the electrical control cabinet, each component is further divided into several sub-components. Finally, according to the wiring relationship of the electrical schematic diagram, the input and output wire numbers of 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. The drawings should schematically show the location of the main components of each part, the wiring relationship of each part, the wiring method, 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 ensure the entire electrical control system is centralized and compact. Where space permits, heat-generating components and electrical parts with high noise and vibration should be placed as far away from or isolated as possible from other components. For large, multi-station equipment, 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 convenient and easily visible locations. The rationality of the overall configuration design directly affects the manufacturing and assembly quality of the electrical control system, and further influences the performance, reliability, ease of operation, debugging, and maintenance of the electrical control system.
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 closely related wiring 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 the inspection and debugging of the electrical control system, components that require frequent adjustment, maintenance, and are prone to damage are grouped together.
2. When dividing the electrical control cabinet components, it is necessary to address the issues between components, between electrical boxes, and between electrical boxes.
Wiring methods between the controlled device and the electrical control cabinet: The wiring methods between the various parts and components of the electrical control cabinet should generally follow the following principles:
(1) The incoming and outgoing lines of switchgear and control panels are generally connected using 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 using terminal blocks or industrial connectors.
(3) Low-voltage control components and printed circuit board components should be connected using various types of standard connectors.
(4) For electrical cabinets and control cabinets, the connections between components within the cabinets (units) can be made directly using the components' own terminals. Transitional connections should use terminal blocks, and the ends should be treated with terminals of appropriate specifications.
III. 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 assembly, large and heavy electrical components should be installed below the electrical board, while heating elements should be installed at the top or rear of the electrical control cabinet. However, thermal relays should preferably 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, shortest wiring length, and good heat dissipation.
(2) High-voltage and low-voltage circuits should be separated and properly shielded to prevent external interference.
(3) Electrical components that require frequent maintenance, inspection, 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 safety clearance into account and be neat, aesthetically pleasing, and symmetrical. Electrical components with similar dimensions and structures can be placed together to facilitate processing, installation, and wiring. If cable trays are used for wiring, the spacing between rows 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 phase.
(6) In the electrical layout design, the number of incoming and outgoing lines of this component should be considered, and the wire specifications and outgoing line positions should be selected to determine the incoming and outgoing line methods, terminal blocks, connectors or plugs, and the wiring numbers of the incoming and outgoing lines should be marked in a certain order.
IV. 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 labeled 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 the 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) Electrical wiring diagrams shall be drawn using fine lines. There are two wiring methods: front-panel wiring and rear-panel wiring. Front-panel wiring is generally used. For simple electrical control components with a small number of electrical elements and uncomplicated wiring relationships, the connections between components can be drawn directly. For complex components with a large number of electrical elements and complex wiring, wiring ducts are generally used. Only the wiring numbers need to be marked on each electrical element; 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, connectors should be used for the entry and exit of large cross-section wires, while other connections should be made via terminal blocks.
V. 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 dimensions and structural type of the electrical control cabinet based on operational needs and the dimensions of various electrical components within the control panel, cabinet, and box. Under normal circumstances, the overall dimensions 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 internal mounting brackets, and mark the dimensions of the mounting holes, mounting bolts, and grounding bolts, while also indicating the connection method. The materials for the cabinets and boxes should generally be dedicated profiles for cabinets and boxes.
(3) Based on the requirements of on-site installation location, operation, and maintenance convenience, design the opening method and type of the electrical control cabinet:
(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 the electrical control cabinet, suitable lifting hooks should be designed or movable wheels should be designed at the bottom of the cabinet. In short, according to the above requirements, a rough sketch of the electrical control cabinet should be drawn first, the dimensions of each part should be estimated, and then the outline drawing should be drawn to scale. Further adjustments to the proportions of each dimension should be made based on considerations of symmetry, aesthetics, and ease of use. After the exterior of the electrical control cabinet is determined, the structural design of each part of the control cabinet should be carried out according to the above requirements. A general assembly drawing of the cabinet and drawings of each door, control panel, base plate, mounting bracket, decorative strip, etc., should be drawn, and the processing requirements should be noted. Appropriate door locks should be selected for the electrical control cabinet as needed. Of course, electrical cabinets have different shapes and structures, and the advantages of various types should be considered in the cabinet design. For non-standard electrical installation parts, part drawings should be drawn according to the design requirements of mechanical parts. 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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