Monitoramento de condições térmicas de transformadores do tipo seco – Análise Técnica e Guia de Aplicação

• Enrolamentos e núcleos de ferro de transformadores do tipo seco, como transformadores de resina fundida e transformadores de resina epóxi, são as principais fontes de calor.. A sua condição térmica determina diretamente a vida útil do isolamento. Para cada aumento de 6°C na temperatura do ponto quente dos enrolamentos, a vida será reduzida pela metade.
• O monitoramento de transformadores isolados a ar e transformadores de isolamento sólido precisa capturar com precisão a temperatura de cada componente de aquecimento. Os métodos tradicionais têm limitações, e a fibra óptica fluorescente tem o melhor desempenho abrangente entre as novas tecnologias de detecção.
• Este artigo analisa tecnologias de monitoramento de condições térmicas para diferentes tipos de transformadores do tipo seco, compara diferentes esquemas, e fornece pontos de seleção e aplicação para ajudá-lo a dominar métodos de monitoramento eficientes.

1. Main Heating Components and Causes of Heat Generation in Dry-type Transformers

Whether it is Cast resin transformers, Epoxy resin transformers, Air-insulated transformers, or Solid insulation transformers, heat is mainly generated from energy loss during power conversion. The core heating components and mechanisms are as follows:

1. Enrolamentos (the most important heat source):Copper loss (I²R) generated when current passes through the windings is the main heat source for all types of dry-type transformers. For Cast resin transformers, their windings are tightly wrapped by epoxy resin, so the heat dissipation condition is more complex than that of Air-insulated transformers, and heat is easy to accumulate to form hot spots. The winding insulation layer of Epoxy resin transformers will accelerate aging due to high temperature for a long time. When the load current increases (such as overload operation), copper loss increases in square proportion, and the temperature rises sharply. Além disso, leakage flux between turns and layers of the windings will generate eddy current loss, further aggravating heat generation. High-voltage windings are more prone to hot spots due to more turns, thinner wires, and larger heat generation per unit volume.
2. Iron core:The iron core generates iron loss in the alternating magnetic field, including hysteresis loss and eddy current loss. This characteristic is particularly obvious in Solid insulation transformers – the thermal conductivity of solid insulation materials is relatively poor, and if the heat of the iron core cannot be dissipated in time, local overheating may occur. Hysteresis loss is related to the area of the hysteresis loop of the iron core material, and eddy current loss is caused by eddy current (corrente circulante) induced in the iron core. If the insulation of iron core silicon steel sheets is poor or the laminations are loose, eddy current loss will increase significantly, levando ao superaquecimento local.
3. Lead wires and connection parts:Poor contact at connection parts such as winding leads and tap changers will generate contact resistance, causing additional Joule heat. This kind of heat generation is more likely to be ignored in Air-insulated transformers because their insulation depends on air gaps, and overheating at contact points may directly affect insulation performance. While the connection parts of Cast resin transformers are covered by insulation materials, so the heat generation is more hidden and may rise suddenly under normal load, which is a common cause of local overheating faults.
4. Cooling fans (auxiliary heating):Forced air-cooled Epoxy resin transformers or Solid insulation transformers, their fan motors will generate a small amount of heat during operation, but the proportion is very low (geralmente <1%). The main impact is that when the fan fails, the heat dissipation efficiency will be reduced, indirectly aggravating the temperature rise of other components. For naturally cooled Air-insulated transformers, the lack of fans makes them more dependent on the heat dissipation design of the windings themselves, so temperature monitoring of heating components is particularly critical.

The heat generation of these components interacts with each other: o calor dos enrolamentos é transferido para o núcleo de ferro por condução, e o calor do núcleo de ferro é dissipado para o ambiente circundante através de convecção. Se algum link de dissipação de calor estiver bloqueado, isso desencadeará uma reação em cadeia, levando à temperatura geral失控.

2. Princípio de funcionamento do sistema de monitoramento de condições térmicas para transformadores do tipo seco

O monitoramento da condição térmica de transformadores do tipo seco determina se o equipamento está em uma faixa operacional segura, captura em tempo real da distribuição de temperatura e tendência de mudança de cada componente de aquecimento. Sejam transformadores de resina fundida ou transformadores isolados a ar, a lógica central é a mesma: perda de equipamento (perda de cobre, perda de ferro) é convertido em calor. Se a taxa de dissipação de calor for inferior à taxa de geração de calor, a temperatura continuará a subir, eventually leading to aging and failure of insulation materials (such as epoxy resin, solid insulation materials).

The monitoring system usually consists of three parts:

1. Camada de detecção: Directly contact or be close to heating parts (como enrolamentos, iron core connection points) to convert temperature signals into transmittable electrical or optical signals. For Cast resin transformers, it needs to be able to penetrate the insulation layer for accurate temperature measurement. For Air-insulated transformers, it needs to adapt to the impact of dust in the open environment.
2. Transmission layer: Transmit signals to the processing unit through cables, fibras ópticas, or wireless means. Due to the compact insulation structure of Solid insulation transformers, there are higher requirements for the wiring space of transmission lines.
3. Analysis layer: Real-time analysis of temperature data, and trigger an alarm when exceeding the threshold (such as the hot spot temperature upper limit of 155℃ for Epoxy resin transformers, which can be appropriately relaxed for Air-insulated transformers due to better heat dissipation but needs strict monitoring).

Entre eles, o type of sensing layer technology is the core factor determining the monitoring effect, directly affecting the accuracy and reliability of data.

3. Comprehensive Comparison of Thermal Condition Monitoring Technologies for Dry-type Transformers

Different thermal condition monitoring technologies have significant performance differences in scenarios of different types of dry-type transformers such as Cast resin, Epoxy resin, Air-insulated, and Solid insulation. The following is a comparison of key parameters of mainstream technologies:

Tecnologia de monitoramento	Princípio de detecção	Faixa de medição de temperatura	Anti-electromagnetic Interference Ability	Método de instalação	Estabilidade a longo prazo	Nível de custo	Adaptability to Different Types of Transformers	Core Shortcomings
Termistor (PT100)	A resistência do metal muda com a temperatura	-50~200℃	Pobre	Surface pasting / lead wiring	Pobre (needs calibration every 3-5 anos)	Baixo	Only suitable for surface temperature measurement of Air-insulated transformers, cannot penetrate the resin layer	Cannot monitor internal hot spots of windings; leads are susceptible to electromagnetic interference
Infrared thermometer	Receives infrared radiation to calculate temperature	-20~300℃	Forte	Sem contato (instalação externa)	Médio (affected by environmental dust)	Médio	General adaptability to Air-insulated transformers, cannot penetrate the insulation layer for Cast resin transformers	Needs to open the observation window, susceptible to environmental temperature and humidity interference
Grade de fibra Bragg	O comprimento de onda da reflexão da grade muda com a temperatura	-40~150℃	Forte	Implant into windings / pasting	Médio (prone to drift at high temperature)	Alto	Suitable for Solid insulation transformers, but susceptible to material stress in Cast resin transformers	Complex demodulation equipment, multi-point monitoring needs series connection leading to single point failure affecting the whole
Wireless sensor	Sinal de radiofrequência transmite dados de temperatura	-30~125℃	Pobre	Surface adsorption	Pobre (vida útil da bateria 1-2 anos)	Médio	Can be tried for Air-insulated transformers, easy to shield signals for Cast resin transformers with metal shells	Battery fails quickly in high temperature environment, data is easy to lose
Fluorescent optical fiber	Fluorescence decay time changes with temperature	-30~200℃	Extremamente forte	Implant into windings	Excelente (maintenance-free for more than 10 anos)	Médio-alto	Suitable for all types, especially suitable for internal temperature measurement of Cast resin and Solid insulation transformers	Optical fiber wiring needs professional design, with requirements on bending radius
Fibra óptica distribuída	Reflexão óptica no domínio do tempo (OTDR)	-50~250℃	Forte	Lay along windings	Médio (a precisão diminui com a distância)	Alto	Suitable for large Air-insulated transformers, insufficient space in compact Solid insulation transformers	Cannot locate specific hot spots, only can measure regional temperature

Conclusão: Fluorescent optical fiber technology has the best comprehensive performance in thermal condition monitoring of various dry-type transformers, especially in three core dimensions: internal hot spot capture of Cast resin transformers, anti-interference ability of Air-insulated transformers, and long-term stability of Solid insulation transformers, which are far superior to other technologies.

4. Core Technical Points of Thermal Condition Monitoring for Dry-type Transformers

Effective thermal condition monitoring needs to meet the special operating environment of different types of dry-type transformers. The following points determine the reliability of the system:

1. Accurate monitoring adapted to insulation type:Sensores para transformadores de resina fundida precisam ser implantados nos enrolamentos envoltos em resina epóxi para medir diretamente os pontos quentes; Os transformadores isolados a ar precisam considerar o impacto da poeira nos sensores e selecionar modelos antipoluição; Transformadores de isolamento sólido, devido à sua estrutura compacta, requerem sensores com diâmetro <2mm para evitar danos ao isolamento.
2. Design antienvelhecimento para características do material:O sistema de monitoramento para transformadores de resina epóxi precisa suportar a estabilidade química de longo prazo da resina epóxi após a cura, e o material do sensor não deve reagir com a resina; sensores para transformadores isolados a ar precisam ter desempenho à prova de poeira e umidade para se adaptarem ao ambiente aberto.
3. Configuração de limite diferenciado:Diferentes materiais de isolamento têm diferentes níveis de resistência ao calor. Epoxy resin belongs to Class F (hot spot upper limit 155℃), and some solid insulation materials can reach Class H (180℃). The monitoring system needs to preset corresponding thresholds according to the transformer type to avoid false alarms or missed alarms.
4. Protection of insulation performance during installation:When implanting sensors into Cast resin transformers, it is necessary to avoid damaging the epoxy resin insulation layer; the wiring of Air-insulated transformers must not affect the insulation distance of air gaps; Solid insulation transformers must ensure that the overall insulation resistance meets the standards after installation.

5. Perguntas frequentes (Perguntas frequentes): Key Questions in Thermal Condition Monitoring Practice

(EU) Adaptability to Different Types of Transformers

1. P: Is wireless sensor suitable for Cast resin transformers?
   UM: Não. Resin and metal shells will double shield wireless signals, resulting in a data loss rate >30%; and its windings are completely wrapped, so wireless sensors cannot be close to hot spots, and the measurement deviation can reach more than 20℃. It is recommended to use fluorescent optical fiber implantation monitoring.
2. P: Is infrared thermometer sufficient for Air-insulated transformers?
   UM: Não. Although Air-insulated transformers have no insulation layer blocking, infrared temperature measurement is greatly affected by environmental temperature, umidade, and dust. The accuracy decreases to ±5℃ on rainy days, making it difficult to capture early overheating (such as 10℃ temperature rise at connection points). It is necessary to monitor key parts with fluorescent optical fiber.
3. P: Will installing sensors on Solid insulation transformers damage the insulation?
   UM: It can be avoided by selecting fluorescent optical fiber sensors with a diameter <2milímetros. Its flexible material can be implanted along the insulation gap. The measured insulation resistance decrease is <0.5%, which meets the IEC standard requirements and will not affect the insulation performance of the equipment.

(II) Technical Application

1. P: Do sensors of Epoxy resin transformers need regular calibration?
   UM: Fluorescent optical fiber sensors do not need calibration. Epoxy resin has strong long-term stability after curing and will not affect the decay characteristics of fluorescent materials. The system can maintain long-term accuracy (±1℃), while thermistors are easy to age in resin environment and need annual calibration.
2. P: Can monitoring data of different types of dry-type transformers be互通ally analyzed?
   UM: Sim. Through a unified data platform, the temperature rise curves of Cast resin transformers and Air-insulated transformers can be compared to analyze the difference in heat dissipation efficiency of different insulation types, providing a basis for transformer selection. No entanto, the transformer type must be marked in the system to ensure the accuracy of the analysis.

6. Top Global Manufacturers of Thermal Condition Monitoring Systems for Dry-type Transformers

Classificação	Nome do fabricante	Principais vantagens técnicas (Adaptability to Different Types of Transformers)
1	Ciência Eletrônica de Inovação de Fuzhou&Companhia de tecnologia., Ltda.	Developed special implantation tools for Cast resin transformers, fluorescent optical fiber sensors have good compatibility with epoxy resin, and the installation pass rate in Solid insulation transformers is 99.5%
2	Huaguang Tianrui	The monitoring system for Air-insulated transformers has IP66 protection level, outstanding dust resistance, and supports sharing data platforms with Epoxy resin transformers
3	Luna Inovações (EUA)	Distributed solutions are suitable for large Epoxy resin transformer clusters, and a single system can be compatible with monitoring of 20 different types of dry-type transformers
4	Opsens Soluções (Canadá)	Sondas fluorescentes resistentes a altas temperaturas (200℃) are suitable for Class H Solid insulation transformers, with a market share of more than 30% in North American Cast resin transformer market
5	Neoptix (Canadá)	Miniature sensors with a diameter of 1.8mm are specially designed for Solid insulation transformers, and the insulation resistance retention rate after installation is >99%
6	Núcleo de fibra (Reino Unido)	Low-loss optical fiber is suitable for long-distance monitoring of Air-insulated transformer clusters, with a signal transmission distance of 10km, reducing relay equipment
7	Óptica Micron (EUA)	The demodulation module can automatically identify the transformer type (Cast resin / Air-insulated), intelligently match the temperature measurement threshold, and reduce manual setting costs
8	Controle de fótons (Canadá)	The sensor material does not react with epoxy resin, and the service life in Cast resin transformers is >15 anos
9	HBM FiberSensing (Portugal)	Thermal-dielectric loss combined monitoring technology is suitable for evaluating the insulation aging state of Solid insulation transformers, with data accuracy >95%
10	Sensortherm (Alemanha)	Customized 3D temperature field simulation algorithm for Epoxy resin transformers, which can predict hot spot migration paths, with more than 2000 application cases in Europe

To obtain thermal condition monitoring schemes, sensor installation diagrams, or insulation material compatibility reports for specific types of dry-type transformers (such as Cast resin transformers, Air-insulated transformers), please submit an inquiry on our website, and professional engineers will provide you with customized solutions.

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