14 Measures to Improve Distribution Transformer Quality

1. Design Requirements to Improve Transformer Short-Circuit Withstand Capability

Distribution transformers should be designed to withstand symmetrical short-circuit currents (thermal stability current) at 1.1 times the current under the most unfavorable three-phase short-circuit conditions. The peak short-circuit current (dynamic stability current) should be designed for 1.05 times the current when short-circuit occurs at the instant of zero terminal voltage (maximum peak current factor). Based on these calculations, the short-circuit mechanical forces on all structural components (windings, core, insulation parts, clamping parts, tank, etc.) can be determined, with sufficient design margins incorporated.

Note: The most common failures found in random inspections relate to short-circuit withstand capability, temperature rise, and load losses. Addressing these three issues is key to improving product quality.

2. Optimizing Heat Dissipation Design for Oil-Immersed Transformers

Ensure that the designed temperature rise of windings and oil surface is at least 5K lower than contract requirements. Specifications and quantity of radiators or corrugated panels should include adequate margins. Oil duct design should position oil channels rationally, set appropriate numbers of support strips, increase oil duct width, and minimize oil stagnation zones within the core assembly. Heat dissipation design should also consider comprehensive impacts on short-circuit withstand capability, insulation, and other parameters.

Note: Transformer tank volume, winding current density, insulation wrapping methods and layers, and radiator cooling area are the main factors affecting temperature rise.

3. Optimizing Dry-Type Transformer Design

To improve short-circuit withstand capability of dry-type transformers, there should be no fewer than 4 effective support points between the low-voltage coil and core. Upper and lower compression blocks should have positioning functions to prevent coil displacement. To control partial discharge in dry-type transformers, the interlayer field strength design should not exceed 2000V/mm.

4. Optimizing Amorphous Alloy Core Transformer Design

For amorphous alloy cores, band materials with high saturation magnetic flux density should be prioritized while ensuring core losses meet design requirements. Epoxy glass fiber cylinders should be added between the low-voltage coil and amorphous core to improve coil structural strength and reduce deformation forces on the amorphous core. Design should avoid excessive differences between the long and short axes of low-voltage windings.

Note: The further the coil shape deviates from circular in amorphous alloy core transformers, the more prone it is to deformation during testing, which increases the likelihood of compressing the amorphous core.

5. Strict Adherence to Transformer Designs Validated by Type Test Reports

Whether using the manufacturer's own design drawings or imported designs, prototypes should be manufactured and type test reports obtained before mass production. Production models should match the drawings and technical parameters of the type-tested sample; otherwise, recalculations and verification must be performed.

Note: For newly introduced design drawings, manufacturers may lack understanding of process control requirements and should conduct trial production first.

6. Strengthening Control of Key Raw Materials Selection

6.1 High-Voltage Windings

Semi-hard copper conductors should be prioritized. Appropriate specifications of electromagnetic wire should be selected to reduce eddy current losses within conductors. Conductor resistivity should meet design requirements with adequate margins. Low-voltage windings should preferably be wound with copper foil.

6.2 Interlayer Insulation

Large diamond-pattern adhesive paper or equivalent materials should be used, properly dried and cured. Ordinary cable paper should not be used.

6.3 Oil Ducts

High-density pressboard laminated support strips should be used for oil ducts. Corrugated oil ducts should not be used.

7. Strengthening Incoming Inspection of Key Raw Materials

7.1 Electromagnetic Wire

Upon arrival, electromagnetic wire should be sampled for wire gauge, enameled wire withstand voltage, resistivity, enamel thickness, and enamel adhesion to ensure electrical and mechanical performance.

7.2 Transformer Oil

Transformer oil must undergo chemical analysis upon arrival.

7.3 Amorphous Alloy Strips

Upon arrival, amorphous alloy strips should be sampled for specific total losses, thickness, and stacking factor.

8. Strengthening Production Environment Management

Manufacturers should strictly control cleanliness in production areas (winding, core, and insulation component workshops) to meet process environmental requirements.

9. Strengthening Coil Manufacturing Process Control

9.1 Winding Equipment

Winding equipment should be equipped with tension control devices. Process standards for conductor winding should be established with layer-by-layer control of coil outer diameter.

9.2 Coil Curing

Coils should be baked and cured with molds to ensure materials like coil adhesive paper are fully cured, forming an integrated structure with high mechanical strength to improve short-circuit withstand capability.

9.3 Drying Process

For assembled coils, specific requirements and strict controls must be established for temperature, duration, and vacuum level during the core drying process.

Note: Differences in personnel technical skills and quality control during processes such as coil winding and core assembly can easily lead to failures in short-circuit withstand capability and temperature rise, significantly affecting distribution transformer quality.

10. Strengthening Amorphous Alloy Core and Clamp Assembly Control

After assembly of amorphous alloy core transformers, the core opening should face downward to prevent amorphous fragments from falling into windings. Amorphous alloy core transformers should use high mechanical strength clamping structures to support windings on a robust frame structure.

11. Vacuum Oil Filling and Enhanced Oil Quality Monitoring

Ensure oil tanks are clean during filling; vacuum oil filling is recommended. Regularly inspect oil tank outlets and conduct oil tests, with at least two checks per month.

12. Strengthening Factory Acceptance Test Quality Control

12.1 Personnel and Equipment

Manufacturers should employ test personnel familiar with relevant test standards and methods. Test equipment and instruments must meet standard precision requirements and undergo verification or calibration by legally authorized metrology institutions.

12.2 Test Coverage

All factory test items should be performed on every delivered product, with test records and copies of factory reports preserved for reference.

Note: Test equipment deviations, non-standard testing methods, or inadequate testing environments can cause significant deviations in test data, leading to不合格 products being shipped. Manufacturers should enhance internal control standards and strictly follow required test procedures.

13. Strengthening Quality Control of Type Tests and Short-Circuit Withstand Capability Tests

13.1 Regular Sampling

Manufacturers should regularly sample products for temperature rise tests, lightning impulse tests, sound level measurements, short-circuit withstand capability tests, and other type and special tests. If test results significantly deviate from design expectations, designs should be reviewed and process controls adjusted.

13.2 In-House Testing

If factory test environments meet relevant standard requirements and comparison results with other qualified laboratories are satisfactory, manufacturers may conduct sampling tests internally, preserving test records and reports for reference.

13.3 External Testing

For tests that cannot be conducted internally, products should be sent to qualified laboratories, with test reports preserved for reference.

Note: Practice is the sole criterion for testing truth. Manufacturer-conducted sampling tests can objectively reveal product quality status.

14. Standardizing Technical Requirements for Raw Materials and Component Procurement

Suppliers should be required to clearly specify in their bidding documents the suppliers, models, key parameters, and origins of main raw materials and components.