Introduction to transformer winding thermometers

Date: July 18, 2025 09:31:40

Transformer Winding Temperature Indicator (WTI for short) is used forDirect monitoring of hot spot temperatures in transformer windingsThe design of the key equipment needs to take into account high-voltage insulation, anti-electromagnetic interference and long-term stability.

1. Principles of operation

  • indirect method of measurement(Mainstream):
    pass (a bill or inspection etc)Current transformers (CT)Take the transformer load current and inject it into the thermometer's internalheating elementThe simulated winding heat. The thermometer sensing package (placed on the top of the transformer tank) measures the oil temperature, superimposed on the simulated winding copper loss heat, and extrapolates theWinding hot spot temperature(usually 10-15°C higher than the oil temperature).
  • direct method of measurement(Fiber optic sensors):
    Pre-buried during winding manufactureFiber Optic Temperature Sensors(e.g. fluorescent optical fiber), direct real-time monitoring of hotspot temperature with ±1°C accuracy, suitable for extra-high voltage or critical transformers.

2. Structural components

  • thermometer bag: Filled with an inert liquid (e.g., xylene) and connected to the dial pointer via a capillary tube that responds to changes in oil temperature.
  • Matching Transformer: The CT secondary current (usually 1A or 5A) drives the heating resistor and simulates the load temperature rise.
  • microswitch: Set alarm (e.g. 120°C) and trip (e.g. 150°C) thresholds and output passive contacts.
  • remote transmission: Optional 4-20mA or RS485 signal access to SCADA system.

3. Key parameters

  • Measurement range: 0-160°C (need to cover insulation class, e.g. class F limit 155°C).
  • accurate: ±2°C (indirect method), ±1°C (fiber optic method).
  • response time: 5-10 minutes for indirect methods (thermal inertia) and seconds for fiber optic methods.

4. Installation and maintenance

  • mounting position: The temperature sensing package needs to be immersed in the transformer oil, avoiding areas of strong magnetic leakage (to prevent additional heat generation from eddy currents).

5. Standards and selection

  • IEC 60076-2: Specify limits for temperature rise in winding hot spots.
  • Selection case::
    • 500kV transformer: Priority is given to fiber optic sensors (e.g. Innotek brand);
    • Distribution transformer (10kV): indirect method thermometer.

6. Emerging technologies

  • Wireless Passive Sensors: Adopting SAW (surface acoustic wave) technology, no batteries are required and the temperature is read via radio frequency, suitable for retrofitting old transformers.
For further exploration of specific scenarios (e.g., adaptation of offshore wind transformers to high salt spray environments), material sealing and corrosion protection designs can be analyzed in depth.
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