Transformer temperature monitoring – All you need to know

Transformer temperature monitoring – All you need to know

Temperature monitoring plays a fundamental role in maintaining the health of transformers, impacting various components. Elevated temperatures can indicate potential faults, posing a risk of further damage if not addressed promptly. It is essential to assess temperatures in different areas of the transformer:

  • Top oil temperature
  • Bottom oil temperature
  • Winding hot spot temperature
  • Ambient temperature
  • External compartment type on load tap changer

Winding insulation, sensitive to temperature and moisture, makes power transformer monitoring the hot spot crucial. This directly impacts the transformer’s aging rate; for every 6˚C increase above the rated maximum of 110˚C, the aging rate approximately doubles.

Methods of monitoring transformer temperature

Traditional temperature gauges

Traditional temperature gauges, such as Oil Temperature Indicator (OTI) and Winding Temperature Indicator (WTI), have been employed since the 1940s for monitoring transformer temperatures. These gauges provide a straightforward and reliable means of assessing the temperature in key areas.

  • Oil Temperature Indicator (OTI): This gauge measures the temperature of the transformer oil. Monitoring the oil temperature is crucial as it reflects the overall temperature conditions within the transformer.
  • Winding Temperature Indicator (WTI): WTI gauges are designed to measure the temperature of the transformer windings. Transformers are often designed with a specific temperature limit for the windings, and the WTI helps ensure that this limit is not exceeded.

While these traditional gauges have been effective, they do require regular maintenance and calibration to ensure accuracy. Mechanical damage to these gauges can lead to inaccurate temperature readings, potentially impacting the efficiency of the transformer’s cooling systems and overall thermal protection. Despite their longevity, these gauges may lack some of the advanced features and remote monitoring capabilities offered by more modern temperature measurement methods, such as electronic temperature monitors (ETM) and fiber optic temperature probes.

Electronic temperature monitors (ETM)

Electronic Temperature Monitors (ETMs) represent a more modern and advanced approach to monitoring transformer temperatures. Unlike traditional analog gauges, ETMs utilize electronic components to provide a range of benefits in terms of accuracy, data management, and remote accessibility. Here are some key aspects of this method:

  1. Accuracy and Precision:
    • ETMs enhance temperature monitoring accuracy by utilizing transformer design information to calculate the winding hot spot temperature. This allows for a more precise assessment of the transformer’s thermal conditions.
  2. Consolidated Data:
    • Instead of relying on separate indicators for oil temperature and winding temperature, ETMs consolidate temperature data. This makes it easier to interpret overall transformer health by having a comprehensive view of temperature conditions.
  3. Remote Monitoring:
    • One of the significant advantages of ETMs is their ability to provide remote data access. This means that temperature data can be monitored and analyzed from a distance. Remote access facilitates timely decision-making and allows for prompt responses to any temperature-related issues.
  4. Detailed Record-Keeping:
    • ETMs often come equipped with robust data recording capabilities. This feature allows for the creation of detailed historical records of temperature variations over time. This historical data is valuable for trend analysis and predictive maintenance.
  5. Fail-Safe Designs:
    • Electronic temperature monitors are designed with reliability in mind. They often include fail-safe features to ensure continued operation even in the case of component failures or malfunctions, reducing the risk of undetected temperature issues.

While ETMs bring numerous advantages, it’s essential to consider factors such as initial costs and the need for periodic maintenance to ensure continued accuracy and reliability. Overall, the shift to electronic temperature monitoring reflects the industry’s move towards more advanced and efficient transformer health management practices.

Fiber optic temperature probes

Fiber optic temperature probes represent a cutting-edge method for monitoring transformer temperatures, offering real-time and direct insight into the thermal conditions of key components. Here are some details about this advanced monitoring technique:

  1. Real-Time Monitoring:
    • Fiber optic temperature probes enable real-time monitoring of transformer temperatures. This means that temperature data is continuously updated, providing immediate awareness of any changes or anomalies in the thermal conditions.
  2. Direct Winding Monitoring:
    • These probes are installed directly in the transformer windings. By being in close proximity to the critical components, they offer a more direct and accurate measurement of the temperature in comparison to traditional methods that may rely on indirect measurements.
  3. Communication with Transformer Monitor:
    • Fiber optic temperature probes utilize light pulse signals to communicate temperature data to a dedicated transformer monitoring system. This communication method ensures reliable and fast transmission of information for timely analysis.
  4. Suitability for Critical Transformers:
    • Fiber optic probes are particularly suitable for monitoring critical transformers where precise temperature control is essential. The ability to directly measure temperatures in the windings makes them valuable for transformers with specific temperature-sensitive components.
  5. Cost-Effectiveness:
    • Despite their advanced capabilities, fiber optic temperature probes are often considered cost-effective, especially for bulk power transformers. The reasonable cost makes them a viable option for installations where accurate temperature monitoring is crucial.
  6. Validation of Thermal Models:
    • By providing real-time data, fiber optic temperature probes help validate thermal models used for predicting the transformer’s behavior under different operating conditions. This validation enhances the accuracy of temperature assessments and contributes to better predictive maintenance strategies.

Integrating fiber optic temperature probes into transformer monitoring systems is becoming more common, especially in situations where the highest level of accuracy and direct measurement is required to ensure optimal transformer health and performance.


By diligently measuring and monitoring transformers, we not only avert potential critical situations but also extend the lifespan of these crucial devices.

At TTES, we have over 100 combined years of experience manufacturing, maintaining, and repairing transformers of all types. If you’re looking for industry-leading lead times of just 20 weeks on average, don’t hesitate and reach out to us for a free quote!

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