Dry-Type Transformer Overheating: Risks, Causes, and Systematic Solutions

Dry-type transformers are widely used in commercial buildings, industrial facilities, and critical applications due to their fire safety, environmental friendliness, and low maintenance requirements. Their operational reliability directly affects power supply continuity, and operating temperature is a key parameter influencing their long-term stability. Overheating not only accelerates equipment aging but can also lead to failures. This article systematically outlines the hazards and root causes of overheating in dry-type transformers and provides comprehensive countermeasures based on engineering practices, covering aspects from design selection to operation and maintenance.

I. Main Hazards of Overheating Operation

The insulation system of a dry-type transformer (typically epoxy resin or vacuum pressure impregnated (VPI) insulation materials) is highly sensitive to temperature. Operating temperatures that exceed permissible limits, whether long-term or short-term, can lead to the following adverse effects:

1. Irreversible Degradation of Insulation Material Performance
The aging of insulation materials follows temperature-dependent chemical reaction rate principles. The widely accepted "8-degree rule" or "10-degree rule" states that within a critical temperature range, for every sustained increase of 8-10°C in operating temperature, the thermal aging life of the insulation material is approximately halved. This means sustained overheating significantly accelerates processes such as molecular chain scission, embrittlement, and cracking of the insulation material, leading to a decline in its dielectric strength and mechanical strength, ultimately increasing the risk of insulation breakdown and internal short circuits.

2. Decline in Electrical and Mechanical Performance

Increased Winding Losses: The resistance of winding conductors increases with temperature. Under the same load current, copper losses generated in the winding (P = I²R) increase, further raising the temperature and potentially creating a vicious cycle.

Compromised Structural Stability: High temperatures exacerbate differences in the coefficients of thermal expansion among different materials (e.g., copper conductor, epoxy resin, core). This can lead to internal stress accumulation, winding deformation, or loosening of support structures. Long-term effects can reduce the transformer's ability to withstand short-circuit electromagnetic forces.

3. Reduced Equipment Service Life and Economic Efficiency
A dry-type transformer designed for a 20-30 year service life will see its actual lifespan significantly shortened if operated under prolonged overheating conditions. This directly reduces the return on investment for the equipment asset and increases lifecycle costs due to unplanned downtime and replacement needs.

II. Common Causes of Overheating Problems

Accurately identifying the source of overheating is a prerequisite for effective management. The main causes can be categorized as follows:

1. Load-Related Factors

Sustained Overload: Operating above rated capacity for extended periods is the most direct cause of winding overheating.

Harmonic Currents: Harmonic currents generated by non-linear loads can significantly increase additional losses in the windings, causing localized overheating. This issue is particularly prominent in applications like data centers and with rectifier equipment.

2. Environment and Installation Conditions

Excessive Ambient Temperature: Standards typically specify an upper limit of 40°C for the ambient temperature around dry-type transformers during normal operation. Higher ambient temperatures directly reduce cooling efficiency.

Insufficient Ventilation and Heat Dissipation: Confined installation spaces, blocked cooling paths, poor room ventilation design, or severe dust accumulation on the transformer surface can all impede heat dissipation.

3. Equipment Condition

Cooling System Failure: For forced air-cooled (AF) type transformers, failure of cooling fans, malfunction of control circuits, or clogged filters can disable the cooling capacity.

Internal Electrical Faults: Issues such as inter-turn winding shorts, loose connections leading to increased contact resistance, or core ground faults can create localized "hot spots." Such problems develop rapidly and are highly hazardous.

Design or Manufacturing Defects: Inefficient thermal design, insulation materials with poor thermal conductivity, or inadequate quality control during manufacturing can also lead to higher-than-normal temperature rise under rated load.

III. Systematic Prevention and Countermeasures

As a transformer manufacturer, AISITE recommends adopting the following systematic measures to manage and control operating temperature throughout the product lifecycle.

1. Initial Selection and Design Stage

Proper Capacity Planning: Select the appropriate rated capacity based on actual load demand, load characteristics (e.g., harmonic content), and expected growth, while considering necessary overload capability. For applications with highly variable loads, products with greater capacity margin can be considered.

Focus on Key Design Aspects: Choose transformer models that utilize high thermal conductivity insulation materials, optimized winding cooling ducts, and have a larger heat dissipation surface area. For high heat-density applications, forced air-cooled (AN/AF) type products can be considered.

2. Professional Installation and Environmental Control
Ensure the transformer is installed in a location meeting the following conditions:

Ambient temperature does not exceed 40°C, and ventilation is adequate.

Sufficient clearance for heat dissipation is maintained around the transformer (typically not less than requirements in technical documentation, commonly 600mm or more).

Avoid direct sunlight, keep away from other heat sources, and clean the equipment surface regularly to maintain cooling efficiency.

3. Comprehensive Temperature Monitoring and Protection
Modern dry-type transformers should be equipped with a reliable temperature monitoring system, typically including:

Direct Winding Temperature Monitoring: Provides direct and accurate temperature measurement via PT100 platinum resistance sensors embedded at the hottest spots within the low-voltage and high-voltage windings.

Intelligent Temperature Control Device: This device should be configured with at least two-stage alarms:

High-Temperature Alarm (e.g., 130°C): Alerts operators to check load or cooling systems.

Overtemperature Trip (e.g., 150°C–170°C, depending on insulation class): Automatically disconnects the power supply, providing final protection.

All alarm signals should be capable of remote transmission to a monitoring system.

4. Standardized Operation and Maintenance

Load Management: Avoid prolonged overload operation. Monitor load current to keep it within the rated range.

Regular Inspections:

Periodically check the operational status of cooling fans (for AF type).

Regularly clean dust from the transformer surface and air inlets/outlets using dry compressed air.

Schedule comprehensive inspections by qualified personnel (e.g., annually), including checks for tightness of electrical connections, insulation resistance tests, etc.

Post-Fault Assessment: If a transformer trips due to overheating, the root cause must be thoroughly identified and eliminated (e.g., checking for internal faults, repairing the cooling system) before a qualified professional assesses its insulation condition. Re-energizing should only occur after confirmation of acceptability.

Conclusion

Managing overheating in dry-type transformers is a systematic engineering task spanning equipment selection, installation, monitoring, and maintenance. The core principle is understanding the decisive impact of temperature on insulation lifespan and controlling the operating temperature within permissible limits through scientific design, appropriate application conditions, and consistent preventive maintenance.

Selecting transformer products with robust thermal design and high manufacturing quality forms the foundation for ensuring long-term reliable operation. By implementing the systematic measures outlined above, the risks associated with overheating can be effectively controlled, ensuring the stability of the power supply system and maximizing the transformer's service life and investment value.