Our company, Dayuan Power, is a transformer manufacturer in China. Users need detailed parameters of various types of transformers to obtain quotations. The manufacturing process of transformers is complex. Our company strictly follows the procedures for production. Below are the steps of the process.

Transformer Manufacturing Process

the complete manufacturing process for an oil-immersed power transformer The entire process can be broadly divided into four main stages:

① Core Manufacturing → ② Coil Winding and Insulation Treatment → ③ Final Assembly → ④ Factory Testing and Treatment

Stage 1: Core Manufacturing

The core forms the magnetic circuit of the transformer and is built by stacking laminations of high-permeability silicon steel.

1. Silicon Steel Slitting and Cutting:

Large coils of silicon steel are slit into strips of the required width using a longitudinal cutting line.

These strips are then cut into the desired shapes and sizes (e.g., "E" or "F" shapes) using a transverse cutting line. Modern cutting lines are computer-controlled for high precision.

2. Stacking and Clamping:

The cut laminations are stacked layer by layer, interleaved at the joints to form a closed magnetic circuit. This interleaving significantly reduces magnetic reluctance and eddy current losses at the core joints.

After stacking, the core is tightly clamped using top and bottom frames, clamping plates, and bands, secured with bolts or steel straps to prevent vibration and noise caused by electromagnetic forces during operation.

3. Core Inspection:

The stacking quality is checked for issues like unevenness or excessive gap at the joints.

The insulation resistance between laminations is measured to ensure good interlamination insulation (the silicon steel is coated with an insulating layer), which is crucial for reducing eddy current losses.

Stage 2: Coil Winding and Insulation Treatment

The windings form the electrical circuit of the transformer. This is a core环节 (core link) requiring extremely high precision and insulation reliability.

1. Winding Preparation:

Conductor Preparation: Typically flat or round wire made of copper or aluminum, insulated with enamel (for magnet wire) or paper.

Insulation Preparation: Materials such as insulating paper, pressboard, insulating blocks, and angle rings are prepared for inter-layer, inter-turn, and main insulation.

2. Winding:

The conductor is wound onto a mandrel or insulating cylinder using specialized winding machines. Constant tension and tight winding are maintained throughout the process.

Different winding types are used based on voltage rating and capacity (e.g., layer winding, disc winding - continuous, interleaved, internally shielded). The processes vary accordingly.

Insulating components (e.g., blocks, spacers, angle rings) are placed during winding to form vertical and horizontal oil channels for coolant flow and heat dissipation.

3. Pressing and Drying:

The wound coils (typically low-voltage, high-voltage, and tap windings) are placed in a vacuum drying oven to remove moisture.

After drying, they are pressed to their designed height in a hydraulic press and secured with clamping plates to ensure mechanical strength to withstand short-circuit electromagnetic forces during operation.

4. Insulation Treatment:

Some transformer types require the coils to be impregnated with varnish or resin to further enhance insulation and moisture resistance.

Stage 3: Final Assembly

This stage involves assembling the core, windings, tank, and all other components into a complete transformer.

1. Core Assembly (Stacking onto Windings):

The top clamp of the prepared core is loosened.

Using large hoists, the prepared windings are sequentially (usually low-voltage first, then high-voltage) placed over the core limbs. This is a critical step requiring precision to avoid damaging insulation.

2. Core and Coil Assembly (Active Part Assembly):

After the windings are placed, the core top clamp is re-tightened.

Lead Attachment: The winding leads are connected to the tap changer (switch) and bushing terminals using copper bars or cables. All connections must be secure, and insulation distances must meet specifications.

The tap changer (either off-circuit or on-load) is installed.

3. Active Part Drying:

The assembled active part (core + windings + leads) is placed in a large vacuum drying tank for prolonged hot oil spray circulation and vacuum drying. This is one of the most crucial processes for ensuring the transformer's insulation lifespan, aimed at彻底 (thoroughly) removing moisture from every corner of the active part.

4. Tank Assembly:

The dried active part is quickly lifted into the prepared transformer tank.

All cover-mounted accessories are installed: HV and LV bushings, conservator (oil tank), pressure relief device (rupture diaphragm or valve), Buchholz relay (gas relay), temperature gauges, and radiators (or coolers).

All flange connections are tightened to ensure the tank is sealed.

5. Vacuum Oil Filling:

Evacuation: A high vacuum is applied to the tank to remove residual air and traces of moisture from the active part and tank.

Oil Filling: While under vacuum, purified transformer oil (strictly filtered, degassed, and dehydrated) is injected from the bottom until the active part is fully immersed and the oil level reaches the specified mark.

Stage 4: Factory Testing and Treatment

Every transformer must undergo rigorous testing before leaving the factory to verify its performance meets national standards and contract requirements.

1. Routine Tests ( performed on every unit):

Winding Resistance Measurement: Checks for proper conductor connections and contacts.

Voltage Ratio and Vector Group Test: Verifies the voltage transformation ratio and phase displacement.

Insulation Characteristics Tests: Measures insulation resistance, polarization index, dielectric dissipation factor (tan δ).

Power Frequency Withstand Voltage Test: Tests the main insulation strength.

Induced Voltage Test & Partial Discharge (PD) Measurement: Tests inter-turn and inter-disc insulation strength and measures partial discharge levels. This is a key indicator of insulation quality.

No-Load Loss and Current Measurement: Evaluates core quality and design.

Load Loss and Short-Circuit Impedance Measurement: Evaluates winding design and manufacturing quality.

2. Type Tests (performed on a prototype or sample unit):

Temperature Rise Test: Verifies the cooling performance, ensuring temperature rises of various parts do not exceed limits under rated load.

Lightning Impulse Withstand Test: Simulates a lightning surge to test the insulation strength against overvoltages.

3. Special Tests (as per contract requirements):

Sound level measurement, zero-sequence impedance measurement, short-circuit withstand test, etc.

4. Finishing and Painting:

After passing all tests, some oil is drained to achieve the required level in the conservator.

The tank exterior is cleaned and receives its final coat of paint.

Nameplates and rating plates are installed.

5. Packaging and Shipping:

Depending on the transport mode (road, rail, sea), the transformer is securely packaged and crated to ensure internal structures are not damaged during transit. Large transformers are often filled with dry nitrogen gas for protection during shipping.