Oil-immersed transformers are widely used in power distribution systems due to their high efficiency, strong overload capacity, and reliable insulation performance. However, to ensure long-term stability and operational safety, strict requirements must be followed during installation. This article outlines the key installation requirements for oil-immersed transformers, including site selection, foundation construction, ventilation design, fire protection, grounding, and pre-operation inspection.
1. Site Selection Requirements
The first step in installing an oil-immersed transformer is selecting an appropriate site. The location should meet the following criteria:
Accessibility and Safety: The transformer should be installed in a secure and accessible area, away from public roads, residential zones, and flammable materials.
Environmental Conditions: Avoid areas prone to flooding, corrosive gases, or excessive dust. The ambient temperature should generally be between -25°C and 40°C, and the altitude should not exceed 1000 meters unless specially designed equipment is used.
Space Layout: Allow sufficient space around the transformer for installation, maintenance, oil sampling, and inspection. Typically, a distance of at least 1.5 to 2 meters around the equipment is required.
2. Foundation and Support Base
A firm, level foundation is crucial for transformer stability and vibration control. The foundation must meet the following requirements:
Load Bearing: The concrete base should be able to bear the transformer's weight, including the oil and any seismic loads.
Level and Alignment: The surface should be flat within a tolerance of ±2 mm to ensure even weight distribution and avoid internal stress during operation.
Embedded Grounding: Grounding connections should be reserved within the foundation, and steel reinforcement bars can be used as part of the grounding grid.
Oil Pit or Oil Collection Trough: For outdoor installations, an oil collection pit should be designed under the transformer to prevent environmental contamination in case of oil leakage.
3. Ventilation and Heat Dissipation
Oil-immersed transformers generate heat during operation, and proper ventilation is necessary to prevent overheating:
Indoor Installation: Mechanical ventilation systems (fans, exhaust systems) should be installed to ensure a constant air exchange. The minimum ventilation rate should be calculated based on the transformer's rated loss.
Outdoor Installation: Adequate natural airflow must be ensured. Avoid surrounding the transformer with tall walls or enclosures that hinder heat dissipation.
Heat Isolation: Keep the transformer away from other heat sources and combustible materials to reduce fire hazards.
4. Oil Handling and Leakage Prevention
Transformer oil is a key component of insulation and cooling. Proper handling during installation is critical:
Oil Injection: If oil needs to be added on site, ensure that the oil is properly filtered, free of moisture and particles, and complies with IEC 60296 standards.
Sealing Inspection: All gaskets, flanges, and valves must be inspected for tightness. Oil level indicators and oil conservators must be operational.
Leak Prevention: Use appropriate sealing materials and check for leakage using white paper or UV dye during pressure tests.
5. Grounding and Lightning Protection
Reliable grounding ensures the transformer's electrical safety. Follow these requirements:
Main Grounding: The transformer tank and core must be connected to the main grounding grid. The grounding resistance should typically be below 4 ohms.
Protective Grounding: All exposed conductive parts (e.g., radiators, valves, operating handles) must be bonded to ground.
Lightning Protection: If installed outdoors, install surge arresters and lightning rods to protect against overvoltage and direct strikes.
6. Cable Connection and Busbar Installation
High-voltage and low-voltage connections must be correctly installed according to electrical codes:
Terminal Marking: Ensure proper phase sequence and terminal marking (e.g., A, B, C for HV; a, b, c for LV) according to the wiring diagram.
Cable Routing: Avoid sharp bends and ensure that cable terminations are moisture-proof and oil-resistant. Use cable clamps to relieve mechanical stress.
Busbar Installation: If busbars are used, they must be securely supported, insulated, and allow for thermal expansion.
7. Pre-Commissioning Inspection
Before energizing the transformer, a comprehensive inspection and testing process must be carried out:
Insulation Resistance Test: Measure insulation resistance of windings to ground and between windings using a 2500V or 5000V megger.
Transformer Turns Ratio (TTR) Test: Verify the winding ratio matches nameplate specifications to ensure proper voltage transformation.
Oil Quality Test: Check for dielectric strength, water content, acidity, and breakdown voltage of transformer oil.
Protection Relay Test: If protection devices (e.g., Buchholz relay, pressure relief valve) are equipped, test their response functionality.
Wiring Check: Confirm all terminal connections, control circuits, and protection systems are properly wired and operational.
8. Trial Operation and Monitoring
After installation and testing, the transformer should be put into trial operation with load:
Gradual Loading: Start with 50% load and gradually increase while monitoring temperature, noise, and voltage stability.
Oil Temperature Monitoring: Ensure oil temperature does not exceed specified limits (typically 85°C under normal conditions).
Leak Detection: Continue monitoring for oil leakage, abnormal odors, or pressure changes during the first 24-48 hours of operation.
Proper installation of oil-immersed transformers is essential for safe and stable power system operation. From site selection to grounding, from oil filling to electrical testing, every step must be performed according to standards such as IEC 60076 or ANSI/IEEE C57. Installing transformers correctly not only extends equipment life but also prevents power failures and safety incidents. For large-capacity or special-purpose transformers, it is recommended to work with professional installation teams to ensure compliance with local codes and utility requirements.
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