As core equipment for power transmission and distribution in power systems, the stable temperature control of windings in oil-immersed transformers is directly related to the operational safety, reliability, and service life of the equipment. The following details the temperature standard definition, temperature correlation logic, requirements for different cooling methods, and abnormal handling measures.
1. Core Temperature Standards and Insulation Material Properties
During the operation of oil-immersed transformers, temperature control is a key link in ensuring equipment safety. From the perspective of industry specifications and equipment characteristics, there are clear temperature limits:
Top Temperature Red Line: The top temperature of the transformer must not exceed 95°C. In daily operation, to prevent the equipment from being in a high-load state for a long time, the top temperature is usually required to not exceed 85°C. This standard is set based on considerations of both the thermal stability of transformer oil and the tolerance capacity of winding insulation materials.
Temperature Tolerance of Insulation Materials: Most oil-immersed transformers on the market use Class A insulation materials for their windings. The maximum allowable operating temperature of such insulation materials ranges from 95°C to 105°C. The temperature tolerance of insulation materials directly determines the upper limit of transformer operation; once the temperature exceeds this range, the insulation performance of the material will decline rapidly, and irreversible aging damage may even occur.
2. Temperature Correlation Logic and Calculation Basis
In the temperature monitoring and control system of oil-immersed transformers, there is a clear correlation between the temperatures of various parts, which provides a scientific basis for accurately judging the operational status of the equipment:
Standard Operating Temperature Benchmark: The industry generally adopts 40°C as the standard operating temperature benchmark for transformers. This benchmark value is determined by comprehensively considering the annual ambient temperature range in most regions around the world, ensuring the universality and applicability of the standard.
Temperature Correlation Between Various Parts: Under the standard operating temperature, the average temperature of the winding (including the temperature of the gas around the winding) is 65°C; the temperature rise of the oil at the top of the transformer relative to the surrounding gas is precisely defined as 55°C. From the above data, it can be inferred that the temperature rise of the winding (including the transformer core) relative to the transformer oil is 10°C. This temperature correlation serves as an important basis for calculating the winding temperature based on the top oil temperature.
Based on this correlation logic, the temperature status of the winding can be quickly determined: when the top temperature of the transformer is 85°C, combined with the 10°C temperature rise of the winding relative to the oil, the winding temperature is calculated to be 95°C, which is at the lower limit of the allowable temperature for Class A insulation materials; if the top temperature reaches 95°C, the winding temperature will rise to 105°C, which has reached the maximum allowable temperature of the insulation material, and the equipment will then be in a critical operating state.
3. Temperature Control Requirements for Different Cooling Methods
Oil-immersed transformers have different heat dissipation efficiencies and temperature control standards depending on their cooling methods, so targeted operation and control measures need to be formulated:
Forced Oil Circulation Air-Cooled Transformers: This type of transformer achieves cooling through forced oil circulation combined with fans, resulting in high heat dissipation efficiency. Therefore, its temperature control standards are more stringent. During normal operation, when the top temperature is 75°C, the corresponding temperature rise is 35°C—this value is much lower than that of natural cooling methods, reflecting the advantage of the forced cooling system. In daily operation, it is necessary to focus on monitoring the operating status of the oil pumps and fans to ensure the normal operation of the cooling system and prevent abnormal temperature rise due to cooling system failure.
Natural Oil Circulation Air-Cooled Transformers: This type of transformer relies on the natural convection of oil for heat dissipation and is equipped with fans for auxiliary cooling. Additional over-temperature protection devices (such as temperature relays, pressure relief valves, etc.) need to be installed. In terms of temperature control, the top temperature should generally not exceed 85°C frequently, with a maximum limit of 95°C, and the corresponding temperature rise must not exceed 55°C. Since the heat dissipation efficiency of natural convection is greatly affected by ambient temperature and oil flow status, the frequency of temperature monitoring should be increased during high-temperature seasons or peak load periods to prevent temperature exceeding the limit.
4. Hazards of Abnormal Temperature and Emergency Handling Measures
Excessively high temperatures pose significant hazards to oil-immersed transformers, as they not only shorten the service life of the equipment but also may cause serious safety accidents:
Multiple Hazards of High Temperatures: On one hand, excessively high temperatures accelerate the aging of insulation materials, leading to a decrease in mechanical strength and insulation resistance, which may easily result in winding short-circuit faults. On the other hand, high temperatures accelerate the deterioration of transformer oil, increasing the dielectric loss of the oil and reducing its breakdown voltage, thereby causing it to lose its original insulation and heat dissipation functions. Prolonged exposure to high temperatures will significantly shorten the service life of the transformer; equipment originally designed to have a service life of 20 to 30 years may require major repairs or replacement in only about 10 years. At the same time, it may also cause safety accidents such as winding burnout and oil tank explosion, resulting in large-scale power outages and economic losses.
Abnormal Handling Process: During the operation of the transformer, operation and maintenance personnel need to continuously monitor temperature changes through temperature monitoring devices (such as platinum resistance thermometers, infrared thermometers, etc.). Once it is found that the top temperature, temperature rise, or winding temperature (calculated or directly measured) exceeds any of the above limits, the emergency handling process should be initiated immediately: First, report to the production scheduling department promptly, providing detailed information including the equipment number, location, abnormal temperature value, and current load status. Second, in accordance with the scheduling instructions, take load-limiting measures, such as reducing the electrical load carried by the transformer or transferring part of the load to other transformers, to control the temperature drop by reducing heat generation. At the same time, arrange professional personnel to conduct a comprehensive inspection of the transformer's cooling system, oil level, and presence of leaks to identify the cause of the abnormal temperature. Only after the equipment returns to normal operation can the load be gradually increased.
