How to choose an online transformer temperature monitoring system? Core technology and configuration guide

• Monitoring Objects: Transformer oil temperature (top-of-tank temperature) and winding temperature. Oil temperature reflects the overall heat generation of the transformer, while winding temperature reflects the temperature rise at the hottest internal point; together, these two parameters form the core of transformer thermal condition monitoring.
• Online monitoring method: By installing temperature sensors (PT100 platinum resistance thermometers, thermocouples, or fiber-optic sensors) on transformers and connecting the temperature signals to a temperature controller or monitoring device, 24/7 uninterrupted temperature data collection and remote transmission are achieved.
• The Key Role of the Thermostat: A temperature controller serves as the central hub for temperature monitoring—it displays temperature readings in real time and automatically starts and stops operations based on preset thresholds.Cooling Fans• Issue an alarm signal or trigger a trip protection when the temperature exceeds the limit
• Key to Selection: Select an appropriate temperature monitoring solution based on the transformer type (dry-type/oil-immersed), voltage rating, and cooling method to avoid under- or over-configuration.

1. Basic Methods of Transformer Temperature Monitoring

2. Temperature Monitoring Solution for Dry-Type Transformers

2.1 PT100 Insertion Temperature Sensors

The most common method for temperature measurement in dry-type transformers involves embedding a PT100 platinum resistance thermometer directly within the low-voltage windings or at their ends, with the sensor in close contact with the conductors, ensuring that the measured values most closely reflect the actual temperature of the windings. The temperature controller receives the PT100 signal, displays the temperatures of the three-phase windings in real time, and controls the start and stop of the cooling fans based on preset temperature thresholds.

2.2 Key Considerations for Thermostat Selection

Dry-type transformer thermostatFunctions are identified by letters appended to the model number: D indicates temperature display, E indicates over-temperature alarm, F indicates automatic fan control, G indicates RS485 communication, and I indicates three-phase current monitoring. When selecting a model, choose the appropriate combination of functions based on your actual needs. For example, if remote monitoring is required, you must select a model with G (communication).

2.3 Fiber Optic Temperature Measurement Solutions

Fluorescent fiber-optic temperature measurement utilizes the relationship between the decay time of excited fluorescent materials and temperature, with the fiber-optic probe embedded in the windings to achieve precise temperature measurement. Fiber optics are inherently resistant to electromagnetic interference, making them suitable for use in environments with strong electromagnetic fields. For applications requiring high measurement accuracy, fiber optic solutions can be considered as an upgrade to PT100 sensors.

3. Temperature Monitoring Solution for Oil-Filled Transformers

3.1 Oil Surface Temperature Monitoring (BWY(Series)

The BWY series oil-level temperature controllers are specifically designed to measure and control the oil temperature at the top of transformers. They feature a pointer-type temperature display and incorporate 2 to 6 sets of adjustable electrical contacts to enable alarm, trip, and automatic start/stop control of cooling fans. These controllers are compatible with oil-immersed transformers of various specifications and models and offer excellent protection.

3.2 Winding Temperature Monitoring (BWR(Series)

The BWR series winding temperature meters utilize the thermal simulation principle—by using a heating element to simulate the temperature rise in the windings caused by copper losses, and then adding the oil surface temperature, the temperature of the winding hotspots is indirectly calculated. This approach does not require the installation of sensors inside the windings and has been used in oil-immersed transformers for many years; it is a mature and reliable technology.

4. Frequently Asked Questions FAQ

4.1 Q: Which is more important: oil surface temperature or winding temperature?

A: Both are important, but they focus on different aspects. Oil surface temperature reflects the overall thermal condition of the transformer and the efficiency of the cooling system; it is the most direct temperature indicator during operation. Winding temperature reflects the temperature rise at the hottest internal points and is directly related to the rate of insulation aging. For critical transformers, both should be monitored simultaneously.

4.2 Q: Is the accuracy of PT100 temperature measurement sufficient?

Answer: The PT100 is one of the most established sensors in the field of industrial temperature measurement; its accuracy and reliability fully meet the requirements for transformer temperature monitoring. It offers excellent long-term operational stability and low replacement and maintenance costs.

4.3 Q: Under what circumstances should you upgrade to fiber-optic temperature measurement?

A: Fiber-optic temperature measurement solutions may be considered in the following scenarios: when extremely high accuracy and spatial resolution are required; when the electromagnetic environment is highly complex; when simultaneous multi-point temperature measurement along the windings is needed; or when transformers are operating under extreme temperature conditions.

4.4 Q: How should the alarm and trip temperatures for the thermostat be set?

Answer: Alarm and trip thresholds should be determined based on a comprehensive assessment of the transformer’s insulation class, operating environment, and manufacturer’s recommendations. Generally, for dry-type transformers, the alarm temperature is set between 130 and 150°C, and the trip temperature is set between 150 and 170°C. Specific values should be determined by referring to the equipment manual and operating procedures.

4.5 Q: Does the temperature monitoring system require periodic calibration?

A: Yes. We recommend calibrating the temperature sensors and thermostats once a year to ensure that the deviation between the displayed value and the actual temperature remains within the permissible range. During calibration, use a standard temperature source for comparison, and replace the sensor promptly if a significant deviation is detected.

5. Recommendations for selection

5.1 The standard configuration for dry-type transformers includes a PT100 sensor and a temperature controller; additional features can be selected as needed.

5.2 Oil-immersed transformers come standard with an oil-level temperature controller; critical transformers are equipped with additional winding temperature controllers.

5.3 For applications with specific requirements for temperature measurement accuracy and interference resistance, choose a fiber-optic temperature measurement solution.

Disclaimer: The content of this article is for technical exchanges and reference only, and does not constitute any form of procurement commitment or contract offer. Product technical parameters, configuration programs and prices are subject to the actual signed contracts and technical agreements.

Need a transformer temperature monitoring solution? Contact Innotongda for personalized selection assistance. Service Hotline: 13959168359 (also on WeChat).