Principles, Maintenance, and Repair of Dry-Type Transformers

By azhe July 3rd, 2025 224 views

Dry-type transformers are electrical devices that use air as the cooling medium and do not rely on insulating oil. They are widely used in urban power distribution networks, high-rise buildings, subways, hospitals, data centers, and other locations with high fire safety requirements. Compared to traditional oil-immersed transformers, dry-type transformers offer advantages such as being oil-free, environmentally friendly, fire-resistant, and flexible in installation.

1. Working Principle of Dry-Type Transformers
The operating principle of a dry-type transformer is based on Faraday’s Law of Electromagnetic Induction, just like any other transformer.

Its basic components include:

Core: Made from stacked silicon steel sheets with high magnetic permeability, forming a closed magnetic circuit.
Windings: Divided into primary and secondary windings, typically made of copper or aluminum wire.
Insulation Materials: Encapsulated using epoxy resin, Nomex paper, glass fiber, and other heat-resistant materials.
Enclosure: Provides mechanical protection and a specified degree of ingress protection (e.g., IP20, IP23), while also aiding heat dissipation.
When an AC voltage is applied to the primary winding, it generates an alternating magnetic field in the core, which induces an electromotive force (EMF) in the secondary winding, enabling energy transfer between voltage levels.

Dry-type transformers can be classified by cooling method as:

Air Natural Cooling (AN)
Air Forced Cooling (AF)
2. Maintenance of Dry-Type Transformers
Proper maintenance is essential for ensuring long-term stable operation of dry-type transformers. The following are common maintenance practices:

1. Daily Inspection:
Check for unusual noise or vibration
Monitor for local overheating (use infrared thermometers)
Ensure proper ventilation and clean airflow channels
Inspect terminal connections for looseness, oxidation, or burn marks
2. Periodic Maintenance (every 6 months to 1 year):
Clean dust from windings and ventilation ducts
Measure winding insulation resistance to assess insulation condition
Check for cracks or discharge marks on high/low voltage bushings and connectors
Calibrate temperature controllers and fan control systems
For transformers with fans, check fan operation
3. Key Maintenance Tips:
Always perform maintenance after power-off and with proper safety measures
Use dry, clean tools to avoid damaging insulation layers
Control ambient humidity to prevent moisture absorption
Avoid frequent short circuits or overloads that may damage windings
3. Common Faults and Repair Methods
Although dry-type transformers are simple in structure and highly reliable, they may still encounter the following issues during operation:

Fault Phenomenon Possible Causes Repair Methods
Abnormal Noise or Vibration Loose core, deformed windings, loose clamps Tighten core clamps, replace damaged parts
Local Overheating Poor contact, poor ventilation, overload Check terminal tightness, improve ventilation, reduce load
Unstable Output Voltage Turn-to-turn short, tap changer failure Use turns ratio tester, repair or replace windings
Reduced Insulation Resistance Moisture absorption, aging, contamination Perform drying treatment, replace damaged insulation
Fan Failure Control circuit fault, sensor damage Check fan power supply, thermostat, relay
Recommended Repair Process:
Fault Diagnosis: Preliminary assessment through insulation resistance, DC resistance, and no-load tests.
Power-Off Repair: Ensure complete power disconnection and grounding.
Disassembly Inspection: If necessary, open the enclosure to inspect internal components.
Replacement or Repair: Replace faulty components or rewind windings as needed.
Reassembly and Testing: Reinstall and conduct energization tests to confirm normal operation.
4. Selection and Installation Recommendations
To extend service life and improve efficiency, the following points should be considered when selecting and installing dry-type transformers:

Selection Guidelines:
Choose appropriate rated capacity (kVA) based on load demand
Adjust capacity considering ambient temperature and altitude
Prefer energy-efficient models (Class F or H insulation)
Equip with smart monitoring systems for remote management
Installation Considerations:
Install in well-ventilated areas away from flammable materials
Ensure a flat and stable base to prevent mechanical damage from vibration
Provide reliable grounding to prevent static buildup
Follow wiring standards for high/low voltage terminals to avoid poor contact
5. Future Development Trends
With the development of smart grids and green energy technologies, dry-type transformers are evolving in the following directions:

Smart Upgrades: Integration of IoT modules for remote monitoring, automatic alarms, and condition evaluation.
Energy Efficiency Improvements: Adoption of amorphous alloy cores and nanocrystalline materials to further reduce no-load losses.
Environmental Design: Promotion of halogen-free flame-retardant materials and recyclable structures to reduce carbon footprint.
Miniaturization and Lightweighting: Optimized structural design to increase power density for broader applications.
High-Safety Applications: Suitable for EV charging stations, data centers, and other environments with strict fire/explosion protection requirements.

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