Outdoor 10kV Dry-Type Combined Transformer Vacuum Casting Equipment

Within the vast network of the power system, the 10kV distribution level acts as the city's "capillaries," and is crucially important. The combined transformer, in turn, serves as the precise "sensory nerve" within these vessels, simultaneously undertaking the tasks of voltage and current measurement, providing core data for metering, protection, and control. Outdoor 10kV dry-type combined transformers, owing to advantages such as being oil-free, explosion-proof, maintenance-free, and environmentally friendly, have become the preferred choice for modern distribution networks. Behind their exceptional performance lies a critical manufacturing process – vacuum casting. The vacuum casting equipment that executes this process is the very "precision craftsman" responsible for achieving its superior quality.

I. Why is Vacuum Casting Needed? – The Quality-Decisive Stage

The core of a dry-type combined transformer is formed by encapsulating internal components like coils and iron cores into a solid whole using epoxy resin composite material. This encapsulation layer must meet the following requirements:

• Excellent Electrical Insulation:Withstand 10kV and even higher power frequency and impulse voltages.

• Superior Thermal Stability:Maintain stable performance without aging under harsh outdoor conditions ranging from extreme cold to heat, as well as under self-generated heat.

• High Mechanical Strength:Resist vibration during transportation and installation, and withstand external mechanical impacts.

• Perfect Sealing:Completely prevent the intrusion of moisture and dust, ensuring long-term operational reliability.

If casting were performed under atmospheric pressure, the epoxy resin mixture would entrap a significant amount of air bubbles. After curing, these microscopic bubbles would become weak points in the insulation. Under high electric fields, they are prone to partial discharge. Long-term operation can lead to gradual erosion and carbonization of the insulation layer, eventually causing a breakdown failure.

The vacuum casting process was born precisely to solve this problem. It performs debubbling, mixing, and casting in a high-vacuum environment, capable of thoroughly removing air and volatiles from the resin, ensuring the casting body is dense and flawless. This achieves very high electrical strength and operational lifespan.

II. Core Components and Workflow of Vacuum Casting Equipment

A complete set of vacuum casting equipment is a highly automated system, primarily composed of the following major modules:

1. Raw Material System:

• Storage Tanks:Used for storing epoxy resin, hardener, and other modified fillers separately, equipped with heating and vacuum debubbling capabilities.

• Metering Unit:Utilizes high-precision gear pumps or mass flow meters to ensure the resin and hardener are mixed in strict proportion, which is key to guaranteeing the performance of the cured material.

2. Mixing and Casting System:

• Vacuum Mixing Tank:One of the core components. Under continuous vacuum and agitation, it thoroughly and uniformly mixes the various material components and further removes any bubbles potentially generated during mixing.

• Casting Head and Valves:Connect the mixing tank to the mold, ensuring a smooth, splash-free, and uninterrupted casting process, preventing the secondary introduction of bubbles.

3. Vacuum System:

• Vacuum Pump Set:Typically consists of a Roots pump and a rotary vane pump (or dry pump) forming a two-stage vacuum system, capable of rapidly evacuating the entire system (including storage tanks, mixing tank, mold cavity) to a high vacuum level (usually required to be below 10 Pa).

• Vacuum Piping and Measurement:Equipped with vacuum valves, bellows, and vacuum gauges to monitor and maintain the vacuum level in all parts of the system in real-time.

4. Temperature Control System:

• Heating and Cooling Units:Precisely control the temperature of the raw material tanks, mixing tank, casting pipelines, and even the mold through jackets or coils. Preheating raw materials reduces viscosity, facilitating debubbling and flow. The step-wise heating and curing profile applied to the mold after casting are crucial for ensuring slow, uniform resin curing and reducing internal stresses.

5. Mold and Curing System:

• Specialized Molds:Custom-made according to the transformer's structure, ensuring precise shape and uniform wall thickness of the casting.

• Curing Ovens/Tunnel Furnaces:After casting is complete, the entire mold is placed into curing equipment with a set temperature profile to complete the resin's cross-linking reaction process.

Brief Workflow Description: Prepare Mold & Coils→ Evacuate System→ Preheat & Debubble Raw Materials→ Precise Metering & Mixing→ Casting under Vacuum→ Release Vacuum & Demold→ Programmed Heating & Curing→ Demolding & Cleaning.

III. Technical Advantages of Modern Vacuum Casting Equipment

Compared to traditional equipment or manual operations, modern vacuum casting equipment demonstrates significant advantages:

• Superior Product Quality:Fundamentally eliminates internal bubbles, significantly increases the partial discharge inception voltage, and allows the product's partial discharge level to be controlled at a very low level (e.g., <5 pC), ensuring stable and reliable electrical performance.

• High Automation and Consistency:The entire process is controlled by PLC (Programmable Logic Controller) or industrial computers, eliminating human factor interference and ensuring every transformer leaving the factory possesses highly consistent, premium quality.

• Excellent Material Utilization:Precise metering and enclosed transportation reduce material waste and loss.

• Improved Production Environment:The fully enclosed system avoids the volatilization of irritating chemicals, protects employee health, and meets environmental requirements.

• Comprehensive Data Traceability:The system can record and store the process parameters (vacuum level, temperature, time, ratio, etc.) for each production batch, providing data support for quality analysis and product traceability.

IV. Development Trends and Outlook

With the advancement of smart grids and the "Dual Carbon" goals, higher demands are placed on the performance and reliability of transformers. Vacuum casting equipment is also continuously evolving:

1. Intelligence and Informatization:Deep integration with the Industrial Internet of Things (IIoT) enables remote monitoring of equipment status, fault early warnings, cloud-based optimization of process parameters, and adaptive adjustments.

2. Higher Precision and Efficiency:Development of more precise metering pumps and more efficient mixing heads to shorten production cycles while enhancing accuracy.

3. Compatibility with Eco-friendly Materials:Adaptation to new environmentally friendly, bio-based epoxy resin systems, requiring equipment materials to have better chemical resistance.

4. Flexible Production:Ability to quickly adjust parameters to adapt to flexible production needs for multiple varieties and small batches, meeting market customization trends.

The outdoor 10kV dry-type combined transformer vacuum casting equipment, though located in a corner of the factory, is an unsung hero ensuring the safe, stable, and efficient operation of the distribution network. With its precise, stable, and intelligent process, it transforms liquid resin into a sturdy and reliable insulating armor, guarding the grid's "sensory nerves." As technology continues to advance, this "precision craftsman" is destined to contribute indispensable core manufacturing power towards building a stronger, smarter future power grid.