production process of dry-type transformers

The production process of dry-type transformers involves multiple key links, with the core objectives being

 to ensure insulation performance, heat dissipation efficiency, and operational reliability. The following are 

the main production processes and technical key points:

### I. Design Stage

1. **Electromagnetic Design**

   - Calculate the cross-sectional area of the iron core, the number of turns of the winding, and the wire 

specifications (such as the diameter of the enameled wire) according to the rated capacity, voltage level, 

and efficiency requirements.

   - Use Finite Element Analysis (FEA) to optimize the magnetic field distribution and reduce magnetic leakage 

and losses.

2. **Structural Design**

   - Determine the winding arrangement method (concentric or overlapping) and the cooling method (natural

 air cooling or forced air cooling).

   - Design the insulation system and select materials such as epoxy resin, Nomex paper, and fiberglass.

### II. Material Preparation

1. **Iron Core Materials**

   - Use high-permeability silicon steel sheets (such as 30Q130), with a thickness typically ranging from 0.3mm 

to 0.5mm.

   - Coat the surface of the silicon steel sheets with a thin insulating paint (such as H-grade silicone paint) to

 reduce eddy current losses.

2. **Winding Materials**

   - High-voltage winding: Use enameled copper wires (such as QZY/180 grade) or foil windings (copper foil

 + interlayer insulation).

   - Low-voltage winding: Mostly use copper foil or flat copper wires to ensure low resistance.

3. **Insulation Materials**

   - Main insulation: Epoxy resin (vacuum pressure casting), Nomex paper (high-temperature resistant), and 

fiberglass reinforced materials.

   - Auxiliary insulation: Insulating tape, molded parts (such as insulating cylinders, spacers).

### III. Winding Production

1. **Winding Process**

   - **Manual Winding**: Suitable for small-capacity transformers. It is necessary to control the tension evenly

 to avoid damage to the enameled wire.

   - **Automated Winding Machine**: Used for high-voltage windings to precisely control the number of turns

and interlayer insulation (such as padding a 0.1mm polyester film for each layer).

2. **Winding Curing**

   - **Epoxy Resin Casting**:

     - Preheat the winding to 80-100°C and inject epoxy resin in a vacuum environment.

     - Cure at a high temperature (120-150°C) to form a high-strength, corona-resistant integral insulation layer.

   - **Nomex Paper Wrapping**: Suitable for transformers above H-grade. Wrap the winding with multiple layers

 of Nomex paper and then hot-press it into shape.

### IV. Iron Core Processing

1. **Silicon Steel Sheet Cutting**

   - Use a numerical control punch or laser cutting to ensure that the burrs ≤ 0.05mm to avoid local overheating

 of the iron core.

2. **Iron Core Stacking**

   - Stack the laminations in a stepped manner (with staggered joints) to reduce the air gap in the magnetic circuit.

   - Bind with through bolts or non-woven fiberglass ribbons to ensure mechanical strength.

### V. Assembly and Testing

1. **Winding and Iron Core Assembly**

   - Fit the winding over the iron core column, adjust the axial and radial positions of the winding, and fix it with 

insulating spacers.

   - Connect the high-voltage and low-voltage leads, and use bolt crimping or welding to ensure low contact 

resistance.

2. **Cooling System Installation**

   - Natural air cooling: Install heat sinks or air ducts.

   - Forced air cooling: Configure fans and temperature control devices.

3. **Factory Testing**

   - **Electrical Performance**: Winding DC resistance test, turns ratio and polarity verification, withstand voltage 

test (such as 3kV/1min).

   - **Temperature Rise Test**: Simulate the operation under rated load and monitor the temperature rise of the 

winding and the iron core (F-grade ≤ 100K, H-grade ≤ 125K).

   - **Partial Discharge Test**: Ensure that the discharge amount ≤ 10pC (10kV level).

### VI. Special Process Technologies

1. **Vacuum Pressure Impregnation (VPI)**

   - Immerse the winding in epoxy resin in a vacuum environment to remove air bubbles and improve moisture 

resistance and voltage resistance.

2. **Foil Winding Technology**

   - Alternately stack and wind the copper foil and interlayer insulation to reduce the winding resistance and leakage

 inductance, which is suitable for transformers with large currents.

3. **Three-dimensional Rolled Iron Core**

   - Adopt a ring-shaped iron core with a seamless design to reduce no-load losses (more than 30% lower than

 traditional laminated iron cores).

### VII. Key Points of Quality Control

1. **Insulation Resistance Detection**: The insulation resistance between the winding and the iron core and between 

the windings ≥ 1000MΩ (measured with a 1000V megohmmeter).

2. **Epoxy Resin Curing Degree**: Ensure that the curing rate ≥ 95% through infrared spectroscopy analysis.

3. **Mechanical Strength**: The axial compressive strength of the winding ≥ 50MPa, and the short-circuit resistance 

meets the IEC 60076 standard.

### VIII. Typical Application Scenarios

- **Power Distribution Field**: Places with high fire protection requirements such as high-rise buildings, subways, 

and hospitals.

- **Industrial Field**: Power isolation of precision electronic equipment and CNC machine tools.

- **New Energy Field**: Boosting/buckling modules of photovoltaic inverters and energy storage systems.

### Conclusion

The production process of dry-type transformers takes **insulation treatment** and **heat dissipation design** as

 the core. Through material innovation (such as epoxy resin, Nomex paper) and process optimization (such as VPI, foil 

winding), the balance between high reliability and compact design is achieved.