Can Excessive Temperature Rise Melt Transformer Insulation Materials?

— A Complete Guide to Temperature Rise Parameters

As a critical parameter in transformer operation, temperature rise directly impacts the safe operation and service life of the equipment. This article provides a comprehensive analysis of the core concepts, influencing factors, international standards, and optimization measures related to transformer temperature rise. It aims to help you deeply understand this key parameter and avoid severe accidents such as insulation material melting caused by excessive temperature rise.

Content

1. Basic Concepts and Importance of Transformer Temperature Rise

Transformer temperature rise refers to the difference between the internal temperature of a transformer under rated load (once thermal stability is achieved) and the ambient temperature. This parameter is crucial because it directly determines the aging rate of insulation materials and the transformer's lifespan.

When the temperature rise exceeds design limits, the aging rate of insulation materials doubles for every 8-10°C increase. This phenomenon is governed by the Arrhenius reaction rate theory, expressed by the formula:

Aging Rate = A × e^(-Ea/RT)

Where:

•         A: Pre-exponential factor

•         Ea: Activation energy (J/mol)

•         R: Ideal gas constant (8.314 J/mol·K)

•         T: Absolute temperature (K)

Table 1: Temperature Rise Class Data

2. Main Causes of Excessive Temperature Rise

● Overloading Beyond Design Capacity

According to Ohm's Law (I=V/R), current passing through a conductor generates heat, following Joule's Law (Q=I²Rt). When a transformer is overloaded beyond its rated capacity, heat generation from winding resistance increases quadratically. For example, a load increase from 100% to 120% raises heat output by 44%. This overload leads to heat accumulation exceeding cooling capacity, causing temperature rise to surpass design limits rapidly.

● Reduced Cooling System Efficiency

Transformer cooling efficiency follows Newton's Law of Cooling:

q = hAΔT

 where:

-q: Heat dissipation rate

-h: Heat transfer coefficient

-A: Heat dissipation area

-ΔT: Temperature difference

Blocked radiators, poor oil circulation, or fan failures significantly reduce h. Data shows that a 1mm dust layer on radiators can decrease cooling efficiency by 20-30%.

● High Ambient Temperature

Per IEC 60076-7, transformer rated capacity is based on ambient temperatures ≤40°C. Poor ventilation or high ambient temperatures reduce ΔT, weakening heat dissipation. For instance, a rise from 30°C to 45°C may increase winding temperature rise by 15-20°C under the same load.

● Insulation Material Degradation

The thermal conductivity (λ) of insulation materials decreases with aging. For example, fresh oil-paper insulation has λ ≈ 0.15-0.18 W/(m·K), but severe aging can reduce it below 0.10 W/(m·K). This degradation creates localized hotspots, triggering a vicious cycle: higher temperature → accelerated aging → further reduced thermal conductivity → even higher temperature.

3. Consequences and Risk Assessment of Excessive Temperature Rise

● Insulation Material Melting Mechanism

When temperatures exceed the glass transition temperature (Tg) of insulation materials, polymer chains lose mechanical strength. For example, Nomex paper (Tg ≈ 220°C) rapidly loses tensile strength beyond this point. IEEE reports that ~38% of transformer failures are directly linked to thermal aging.

● Increased Dielectric Loss

The dielectric loss factor (tanδ) of insulation materials grows exponentially with temperature: tanδ = tanδ0 × e^(αT), where α is a material constant. Higher tanδ converts more electrical energy into heat, creating a feedback loop. Data shows tanδ for Class A insulation at 105°C is 3-5 times higher than at 70°C.

● Gas Generation and Oil Degradation

Per Duval Triangle Analysis, when hotspot temperatures exceed 300°C, insulating oil decomposes, producing fault gases like C2H2. Every 10°C rise doubles oxidation rates, increasing acid value (KOH) by 0.03-0.05 mg/g and shortening oil-paper insulation lifespan.

Table 2: Impact of Temperature Rise on Transformer Lifespan

In Summary

Effective temperature rise management requires a holistic approach covering design, operation, and maintenance. Key recommendations include:

•         Regular infrared inspections and oil analysis.

•         Maintaining clean and efficient cooling systems.

•            Building a temperature rise monitoring database for trend alerts.

•         Proactive temperature rise management significantly extends equipment life and reduces failure risks. For tailored solutions, our technical team offers expert support.

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