High-voltage switchgear is a critical piece of equipment in power systems, and its quality directly impacts the safety of power supply and operational reliability. Many people simply see rows of tall, neatly arranged cabinets in the distribution room, unaware of the numerous manufacturing processes they undergo behind the scenes. Today, from the perspective of the original manufacturer—Hunan Electrical Appliance Co., Ltd.—we’ll take you inside the workshop to gain a comprehensive understanding of the entire production process, from steel plate to finished high‑voltage switchgear.

The entire manufacturing process can be summarized as Four stages ： Housing fabrication → Component assembly → Secondary wiring → Factory inspection Each stage determines the cabinet’s final quality.

I. Shell Fabrication: From Steel Plate to Precision Frame

1. Raw Material Preparation

Selection of Cabinet Materials Aluminum-zinc coated steel sheet The sheet thickness typically ranges from 1.5 mm to 2.0 mm. Aluminum‑zinc coated steel not only exhibits significantly superior corrosion resistance compared to ordinary steel sheets but also offers excellent electrical conductivity and heat dissipation. Prior to storage, raw materials must undergo inspection of material certification reports to verify that the grade, thickness, and surface quality meet the specified requirements.

2. CNC Cutting and Punching

The entire steel plate is fed into a CNC turret punch press, where, under computer control, it undergoes high-precision blanking and punching according to the design drawings. All mounting holes, ventilation holes, and cable entry/exit openings are formed in a single stamping operation. The modular hole pattern (with 25 mm spacing) is controlled to within 0.5 mm, laying the foundation for seamless assembly of the cabinet later on.

Tooling fixtures are particularly critical at this stage—they enable precise positioning of the steel plate, Ensure that the reference for multiple stamping operations remains stable. A qualified fixture ensures the repeatability of all hole positions in three-dimensional space, significantly reducing product dimensional deviations.

3. Multi-bend forming

The stamped sheet metal is fed into a CNC press brake for bending and forming. Why does the KYN28 cabinet exhibit excellent stiffness and toughness? The key lies in… Multi-bend forming process — The same edge is bent two to three times to create a complex cross-section, enabling the cabinet to achieve lightweight construction while maintaining adequate strength.

4. Cabinet Assembly

Each component is connected by Riveting and Bolted Joints Assemble into a complete cabinet. Use high-strength galvanized bolts in conjunction with rivet nuts, ensuring that critical load-bearing components are tightened to the specified torque values (typically using bolts of grade 8.8 or higher). The advantages of a modular design include a high degree of component standardization, excellent interchangeability, and ease of mass production.

Once the housing is completed, it proceeds to the surface treatment stage, where it employs Electrostatic powder coating The process involves controlling the coating thickness to 60–80 μm. Following spraying, the coating is cured by high‑temperature baking, resulting in a hard, highly adherent protective layer that exhibits excellent corrosion resistance and aging resistance.

After the shell is manufactured, it must undergo Pre-assembly inspection Only after verifying that dimensional tolerances, door‑panel opening and closing flexibility, grounding continuity, and all other relevant parameters meet the required specifications may the product proceed to the next process step.

II. Component Assembly: Construction of the Primary Circuit

Component assembly, commonly referred to as “wiring once,” is the process that forms the main circuit of the cabinet.

1. Main Busbar Installation

The horizontal main busbar is installed in the busbar room and uses electrolytic copper busbars; the surface finish can be selected according to customer requirements. Bare copper, tinned, or silver-plated . The lapping surfaces of copper busbars must first be subjected to Polishing treatment Remove the oxide layer and apply conductive grease or electrical compound evenly. When tightening the bolts, use a torque wrench to tighten them to the recommended torque— Excessive torque may cause the copper busbar to deform or the screw threads to strip, while insufficient torque can lead to increased contact resistance. When tightening with double bolts, tighten them diagonally in an alternating sequence to ensure uniform stress distribution across the lap joint.

2. Installation of the stationary contact box

The stationary contact box, encapsulated in sulfur hexafluoride or epoxy resin, is mounted on the partition and must be precisely aligned with the hand‑car contact arm, with a deviation not exceeding 2 mm. The inner surface of the contact box shall be kept clean, free of dust or foreign matter; otherwise, partial discharge may occur.

3. Installation of Branch Busbars and Current Transformers

The stationary contact box is equipped with a branch busbar, the other end of which is connected to the current transformer. The installation orientation of the current transformer must conform to the drawings. P1 terminal faces the busbar side, and P2 terminal faces the outgoing line side. . The secondary wiring terminals must be waterproof and sealed.

4. Installation of Earthing Switches and Surge Arresters

The earthing switch is typically mounted on the rear wall of the cable compartment, with its operating mechanism routed to the lower front of the cabinet. The surge arrester is connected in parallel with the main circuit via a copper busbar, while its grounding terminal is separately led to the grounding busbar—grounding conductors should be as short and straight as possible.

5. Handcart Assembly and Commissioning

The circuit breaker handcart is assembled at a dedicated workstation, where the contact arms and flower‑type contacts are inspected for integrity, and the lead‑screw push‑in mechanism is confirmed to be well lubricated. After the handcart is pushed into the cabinet, its smoothness of movement and the accuracy of position indication are tested in both the “test position” and the “working position.” The bolts securing the stationary contact box may loosen due to vibration and fall into the handcart compartment—therefore, they should be coated with… Thread-locking adhesive It is an important measure to prevent loosening due to vibration.

III. Secondary Wiring: The “Nervous System” of the Control Circuit

Secondary wiring determines whether the control, protection, and communication functions are operating properly and is one of the key aspects that directly reflects the quality of a switchgear cabinet.

1. Drawing Review and Material Cutting

Before wiring, obtain the secondary schematic diagram, the terminal block diagram, and the panel component layout drawing. Based on these drawings, prepare a list of wire specifications, colors, and lengths, and use… Multi-strand copper flexible wire — Control circuit cross-section: 1.5 mm²; current circuit: 2.5 mm²; voltage circuit: 1.5 mm².

2. Component Placement and Routing

The instrument panel is equipped with microprocessor-based protection devices, electric energy meters, changeover switches, indicator lights, and other components. All components are clearly labeled for ease of operation. Conductors must be sleeved. Wire numbering tube , Print the content according to the standard numbering, and ensure that wire‑number tubing is oriented consistently for easy reading.

Wire routing principles:

Strong and weak currents shall be routed separately.

Maintain spacing between AC and DC circuits.

Use cable trunking to organize and bundle the wires, and at doorways, use… Bellows wrapping Add cut-resistant sleeve

The ends of the spare core wires shall be sealed with insulating caps.

3. Wiring and Inspection

Crimp cold‑pressed terminals onto both ends of the conductors, and use a crimping tool to ensure a secure, tight connection with no exposed copper. On the terminal block, arrange the conductors by circuit zone, with no more than two wires per terminal. After wiring is complete, verify continuity circuit by circuit, confirming there are no open circuits, short circuits, or incorrect connections.

IV. Factory Inspection: Each cabinet must pass through five rigorous checks.

Prior to shipment, each switchgear cabinet shall undergo rigorous testing in accordance with the national standard GB/T 3906.

1. Visual and Structural Inspection

The cabinet surface coating is free of scratches, runs, and substrate exposure.

The door lock and hinges operate smoothly.

The handcart slides and pushes smoothly, with accurate position indication.

The secondary plug makes good contact and locks securely.

Ground loop continuity test passed.

2. Insulation Resistance and Power-Frequency Withstand Voltage Test

Insulation resistance: Phase-to-phase and phase-to-ground in the main circuit ≥ 1 MΩ/kV (for 12 kV switchgear, ≥ 12 MΩ); measured values typically exceed these specifications by a significant margin.

Power-frequency withstand voltage: Applied to enclosures with a rated voltage of 12 kV. 42kV/1min , no flashover or breakdown

3. Main Circuit Resistance Measurement

Measure the DC resistance of each phase’s main circuit and compare it with the type‑test value; typically, it should not exceed 40 μΩ (for circuits rated at 400 A or higher). An abnormal contact resistance indicates a loose connection at some point.

4. Mechanical Operation and Interlock Testing

Perform 5 to 10 manual and 5 to 10 electric operations for the circuit breaker; operation shall be reliable.

“Five‑Protection” interlock mandatory tests—preventing operation with load on the push‑pull mechanism, preventing erroneous opening or closing of circuit breakers, preventing closing the earthing switch under voltage, preventing energizing the system by closing the earthing switch, and preventing unauthorized entry into live compartments. Each step must meet the requirements.

5. Secondary Function Test

Power-on self-test of the protection device

Simulated fault‑induced verification of protection operation reliability

The indicating instrument displays correctly.

The auxiliary contact status conforms to the drawings.

All test records shall be filed and retained as attachments to the certificate of conformity upon shipment.

V. Packaging and Shipping

Switchgear that has passed testing Hang the certificate of conformity. and affix the nameplate. Disconnect the secondary power plug, and set the handcart to the test position. Secure the accessory box inside the cabinet. The accompanying documentation includes: factory test report, primary/secondary wiring diagrams, certificate of conformity, and installation and operation manual.

The cabinet exterior is wrapped in a dust‑proof plastic film and further protected with corrugated cardboard or a wooden frame. Desiccants are placed in the busbar compartment and the cable compartment to prevent moisture ingress during transit. Transportation is carried out using flatbed trucks or shipping containers, and impact or tilting should be avoided during loading and unloading.

At this point, a qualified high-voltage switchgear has been officially completed.

Professionalism stems from a commitment to every detail.

From design to final delivery, a high-voltage switchgear cabinet undergoes dozens of manufacturing processes, each of which directly impacts its ultimate safety and reliability. The precision of the enclosure fabrication, the skillful assembly of components, the adherence to standardized secondary wiring practices, and the rigor of factory acceptance testing—these seemingly minor details collectively determine the equipment’s performance over the next decade or two.

Hunan Electrical Appliance Co., Ltd. As a leading manufacturer of high-voltage switchgear, we adhere to end-to-end in-house production, rigorously controlling every stage—from steel plates to the finished product. We believe that a quality switchgear is not only built but also thoroughly inspected. We welcome friends from all sectors to visit our facility and witness firsthand the entire manufacturing process of a switchgear cabinet.