Dry-Type Transformers: Structure, Cooling, Installation, And Applications

Dry-Type Transformers: Structure, Cooling, Installation, and Applications
Comprehensive Guide to Modern Electrical Power Solutions

Dry-type transformers are critical components in modern power distribution systems, known for their safety, environmental friendliness, and low maintenance. This article provides an in-depth overview of their structure, cooling methods, installation processes, and advantages over oil-immersed transformers.

Structural Forms of Dry-Type Transformers

1. Open-Type Transformers

   • Designed for dry, clean indoor environments (humidity ≤85% at 20°C).
   • Cooling: Natural air cooling (AN) or forced air cooling (AF).

2. Enclosed-Type Transformers

   • Sealed housing prevents direct exposure to air, ideal for hazardous environments like mines (explosion-proof design).

3. Cast-Resin Transformers

   • Main insulation uses epoxy resin, offering compact size and simplicity. Common for smaller capacities.

Cooling Methods

• Natural Air Cooling (AN):
  Operates continuously at rated capacity with passive heat dissipation.
• Forced Air Cooling (AF):
  Increases output capacity by 50% for short-term overload scenarios (not recommended for sustained overloads due to efficiency losses).

Key Types of Dry-Type Transformers

1. VPI (Vacuum Pressure Impregnated) Transformers
   • Insulation materials (B/F/H-class) treated with advanced vacuum processes.
2. Epoxy Resin-Cast Transformers
   • Dominant design using epoxy resin for high durability and insulation.
3. Resin-Bonded Transformers
   • Less common, with resin-impregnated windings.
4. Hybrid-Insulated Transformers
   • High-voltage windings use cast resin; low-voltage windings use foil or vacuum-impregnated designs.

Advantages Over Oil-Immersed Transformers

1. Safety & Fire Resistance
   • Eliminates fire risks from flammable oil, even under fault conditions.
2. Low Maintenance
   • No oil leakage, aging, or sealing issues; reduces operational costs.
3. Space Efficiency
   • Compact design allows co-location with switchgear in indoor facilities.
4. Simplified Components
   • No oil reservoirs, valves, or explosion vents required.

Installation and Commissioning

1. Pre-Installation Inspection

• Verify packaging integrity, nameplate data, documentation, and physical condition.

2. Mounting Process

• Ensure foundation levelness to minimize vibration noise.
• Secure transformer with welded channel steel brackets for stability.

3. Electrical Connections

• Maintain safe distances for conductors; use flexible joints (≥1000A) to absorb thermal expansion.
• Torque bolts to manufacturer specifications.
• 

4. Grounding

• Connect dedicated grounding bolt to protection earth system. Enclosures and neutral lines (if 3-phase 4-wire) must also be grounded.

5. Pre-Commissioning Tests

• Insulation resistance testing (minimum 1000Ω/V), turns ratio verification, and dielectric withstand tests.
• Test cooling fans and install temperature sensors post-testing.

6. Trial Operation

• Monitor for abnormal noise, overheating, or insulation issues. Avoid prolonged operation in high-humidity environments (RH >70%).

Fault Diagnosis via Sound

• Missing Phase: Uneven humming or no sound during phase activation (check power supply or fuses).
• Tap-Changer Issues: "Zizzling" or "sizzling" noises under load (indicating poor contact).
• Loose Components: "Clinking" or "buzzing" sounds from foreign objects or core vibrations.
• Overload: Low-frequency humming (adjust load or enhance cooling).

Noise Reduction Strategies

1. Cooling System Maintenance
   • Clean debris from fans or replace faulty units.
2. Enclosure Damping
   • Add rubber pads between the enclosure and base to absorb vibrations.
3. Room Acoustics
   • Relocate transformers away from reflective surfaces or install sound-absorbing panels.
4. Foundation Reinforcement
   • Stabilize unstable floors to minimize seismic noise.

Selection Guidelines

1. Load Requirements
   • Use dual transformers for critical (Level I/II) loads. Dedicated units for seasonal or high-impact loads (e.g., HVAC, industrial heating).
2. Environmental Factors
   • Fire Safety: Prioritize non-flammable SC(B)9/10 series for high-rise buildings.
   • Harsh Conditions: Opt for sealed designs in dusty or corrosive environments.
3. Space Constraints
   • Select IP2X/IP40-protected models for combined installation with switchgear.

Conclusion

Dry-type transformers are indispensable in modern power systems, offering unmatched safety, efficiency, and adaptability. Their advantages—ranging from fire resistance to minimal maintenance—make them ideal for urban infrastructure, industrial facilities, and sensitive environments. Proper installation, regular testing, and strategic selection based on load and environmental factors ensure optimal performance and longevity. As demand for sustainable energy solutions grows, dry-type transformers will remain a cornerstone of reliable power distribution.

For technical inquiries or customized solutions, consult qualified engineers and reputable manufacturers.