Optimizing the Power Grid: Fiber Optic Sensors Safeguard Transformers

If there were any doubts about the necessity to monitor the temperature of substation transformers, recent events have highlighted their critical importance. A significant fire in a transformer on the outskirts of London resulted in 60,000 homes losing power and led to the closure of Heathrow, Europe’s busiest airport, causing over 1,000 flight cancellations and widespread inconvenience to hundreds of thousands of passengers.

As the world endeavors to reduce carbon emissions, electrical energy is becoming increasingly pivotal. Central to the global electrical supply is the grid, which operates by transmitting electricity from the generation point to the point of consumption.

At the heart of the grid are power transformers needed to step voltages up and down across the grid. Ensuring safe operation of these transformers requires constant monitoring of their internal winding temperature. The high-voltage environment, which makes conventional sensors impractical, alongside liquid oil cooling that surrounds the transformers, makes it challenging to directly measure a transformer’s winding temperature. 

A widely adopted solution is FluorOptic® Temperature (FOT) measurement technology. This technology is immune to all forms of electromagnetic interference (EMI) and is capable of functioning safely and accurately inside a high voltage power transformer.

Principles of FOT Sensing

FluorOptic or Fiber Optic Temperature (FOT) technology operates by placing the sensing tip in direct contact with the measured object, similar to a thermocouple. However, instead of relying on an electrical voltage change, FOT utilizes light and the principle of phosphorescence to measure temperature.

Phosphor, a material known for its ability to "glow in the dark" when exposed to light, is integral to this technology. One early application of phosphors was the illumination of hands or dials on analog watches, enabling time to be read at night.

Upon exposure to a light source, phosphor accumulates light energy. Once the light source is removed, the material emits the stored energy for a brief duration until it is depleted. This emission period is referred to as the 'decay time,' and its duration is highly sensitive to the phosphor's temperature. This temperature-dependent decay time forms the foundational principle upon which FOT technology operates.

Figure 1. Temperature Converter Module

Figure 2. Thermal Imaging and Monitoring

Figure 4. Probe before installation showing the tip inserted in the spacer.

Figure 5.  Picture after the spacer with probe (in this picture two probes are installed into a single spacer) is inserted into the transformer winding.