How to measure the temperature of transformer windings-INNO

The temperature monitoring of transformer windings is the key to ensuring their safe operation. The following are common temperature measurement methods and precautions, classified by reliability and application scenarios:

1. Direct measurement method (most accurate)

Fiber optic temperature measurement system (recommended)
Principle: Fiber optic sensors (such as fluorescent fibers or FBG fibers) are embedded during winding manufacturing to directly measure the temperature of the wire.
Advantages: Insulation, anti electromagnetic interference, accuracy up to ± 1 ℃, suitable for high-voltage or ultra high voltage transformers (such as 500kV and above).
Case: ABB and Siemens’ high-end transformers commonly use this type of system.
Wireless sensors (emerging technology)
Principle: Micro wireless temperature sensors (such as those based on SAW or RFID technology) are embedded between winding layers and transmit data through wireless signals.
Limitations: Need to address metal shielding and electromagnetic interference issues, currently mostly used for testing transformers.

2. Indirect calculation method (mainstream application)

Thermal simulation calculation (IEC 60076-7 standard)
Method: By measuring the top oil temperature (TOST) and load current, combined with the application of winding hot spot coefficient, it can be used for handover testing or fault diagnosis.

3. Traditional monitoring methods (auxiliary reference)

Oil temperature gauge+winding temperature indicator (WTI)
Principle: The oil temperature sensor is combined with the current transformer (CT) signal to simulate the temperature rise of the winding, with an error of about ± 5 ℃.
Attention: Calibration should be conducted every 3 years to avoid misjudgment caused by CT ratio errors.
Infrared thermal imager (external detection)
Usage: Only applicable to exposed winding ends or oil tank surfaces, considering the effects of oil flow and heat dissipation, with poor accuracy (± 10 ℃).

4. Precautions

Security threshold:
Conventional insulation (Class A): winding hotspot ≤ 105 ℃ (IEC standard).
When overloaded: It is allowed to rise to 130 ℃ for a short period of time (refer to the manufacturer’s curve).
Data comparison: When the difference between direct method (fiber optic) and indirect method (thermal simulation) exceeds 10 ℃, it is necessary to investigate sensor or calculation model errors.
Summary and selection suggestions
New/important transformers: Priority should be given to embedding fiber optic systems.
Transformer in operation: WTI+thermal simulation calculation is used, and resistance method is used to verify during annual power outages.
Temporary monitoring: infrared+wireless sensor combination, suitable for troubleshooting.
For specific equipment models or installation details, please contact FJINNO

The installation difficulty of fiber optic temperature measurement system is moderate, mainly depending on the application scenario (such as transformer winding, switchgear, generator) and installation method (pre embedded vs later installation). Here are the key points:
1. Installation
The transformer winding needs to be embedded with optical fibers during the manufacturing stage, and the internal space of the winding is narrow, requiring high-voltage insulation treatment.
The later installation of switch cabinets/busbars requires only surface fixation without dismantling the equipment, but must avoid areas with strong electromagnetic interference.
2. Precautions
Operation: The fiber optic cable is fragile, and the bending radius must be greater than the value, otherwise it is prone to breakage.
Position limitation: The installation inside the transformer winding needs to be designed in collaboration with the manufacturer and cannot be modified later.
3. Suggestions for simplifying installation
New project: Priority should be given to pre embedded fluorescent fiber optic sensors, which will be integrated by the transformer manufacturer. Users only need to connect the demodulator.
Renovation project: Adopting external fiber optic probes (such as busbars and contacts), fixed with zip ties or thermal conductive adhesive, single point installation can be completed within 30 minutes.
4. Do you need professionals?
Yes: Trained technicians are required to operate, especially in high-pressure environments or precision equipment.
Exception: Low voltage scenarios such as switchgear can be completed by a guided electrician team.
Summary: If the transformer has been put into operation, it is recommended to choose an external fiber optic system (such as busbar monitoring), which is easy to install; If it is a new project, although the pre embedded design is complex in the initial stage, it has higher long-term reliability.