Fiber Optic Hot Spot Temperature Monitoring

Accurate hot spot temperature measurements on power transformers

Accurate hot spot temperature measurements can help identify and isolate paper degradation that is related to transformer aging factors. Increases in consumer demand for electricity also known as, heavy spike loads, will increase the temperature in power transformers (hot spots) and increase the degradation of the insulating paper.

Power Transformer Hot Spot Monitoring with Fiber Optic Temperature Sensor

These thermal effects are a key component to aging a power transformer. [IEEE std. C57.91.1995 / IEC 60076-7:2018]  use Arrhenius formulas for deterioration of organic insulation material with time and temperature.

Qualitrol Power Transformer Oil and Winding Temperature Indicators

Figure 1. Aging Accelerator Factor IEEE, Fundamental Principals of Transformer Thermal Loading and Protection; Joe Perez, ERL Phase Power Technologies, Winnipeg, MB, R3Y 1G4

Describe the Causes of Hot Spot Formation in Transformers

When describing direct winding temperature monitoring, you must look at the Direct Current losses and Eddy losses of the axial and radial type which dissipates in transformer windings as the temperature is not uniform around the windings. Radial Eddy losses are much higher at the top and bottom of windings.

In oil-filled power transformers, circulating oil is hotter at the top of the winding. Adding up these various heat dissipation phenomena will end up causing “hot spots”.  Fiber optic temperature sensors provide accurate and fast readings (within MINUTES) of these temperature fluctuations in direct winding temperature monitoring, especially during peak load effects.

Transformer Temperature Limitations

Higher transformer operating temperature has a direct effect on its aging factor by causing faster paper degradation.

Overheating of insulating paper generates gasses that are dissolved in transformer oil. These dissolved gases are known to cause partial discharge. For more information on dissolved gases and partial discharge, check out this on-demand webinar titled, Investigating the Differences Between Dissolved Gas and Partial Discharge

The highest insulation paper and oil temperature are located at the winding hot spot. Using fiber optic temperature sensors will help power transformer operating temperatures remain stable by providing faster-rising temperature measurement.

How Do You Check the Temperature in a Power Transformer’s Oil with Fiber Optic Temperature Sensors?

Installing fiber optic temperature sensors directing into the winding is the only way to check the temperature in a power transformer’s oil. Direct winding temperature provides faster rising direct winding temperature monitoring. Fiber optic temperature sensors help find causes of hot spot formation in power transformers and improve transformer design.

Complete Direct Winding Temperature Monitoring System

Apart from the fiber optic temperature sensor, the complete direct winding temperature monitoring system will include several other components including Tall Wall Plate (TWP), Optical Feedthroughs, JBox, Extensions, and Monitor. The Tank Wall Plate (TWP) provides a proper mounting point on the transformer’s wall to prevent oil leakage. Optical Feedthroughs installed on the Tank Wall Plate (TWP) allows the monitor light signal to travel to the sensor tip and back to the monitor. The extensions bring the signal back to the monitor where the monitor will read and convert the sensor light signal into a temperature measurement. It can also implement any end-user specific functionality like data-logging, SCADA interconnection, and so on.

Qualitrol Neoptix Fiber Optic Solutions

With over 100,000 installed probes around the globe and extensive field experience, our sensors and monitors are tested for durability and accuracy.

  • Optical feedthroughs are pressure tested to 50 psi
  • Each probe is tested to an accuracy of ±1.0°C over a temperature range of -20°C to 150°C
  • Built to outlast the life of your transformer!

If you are in the process of building a new substation or power transformer, contact us for a Qualitrol Neoptix fiber optic solution.

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