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Fiber Optic Temperature Monitoring for Dry Type Transformer (Cast Resin Transformer)

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Fiber Optic Temperature Monitoring for Dry Type Transformer (Cast Resin Transformer)

Rugged Monitoring (RM) provides cost-effective fiber optic temperature sensors to dry type transformers. The sensors provide continuous real-time monitoring of dry type transformer temperature at winding to quickly detect overload and fault conditions. RM Fiber Optic Temperature Monitor T301 Device offer both analog and digital output, RS-485 Modbus & DNP as well as Copper & Fiber Ethernet communication for simple integration with existing PLCs (Programmable Logic Controllers) and host monitoring software. RM optical temperature sensors provide 100+ years of accurate sensing to ensure safe and efficient dry type transformer operation. 

Utility companies around the world are implementing fiber optic sensors for smart grid temperature monitoring of dry type transformers. These sensors provide real-time temperature data, enabling operators to maximize load efficiency and balance thermal stresses that can lead to catastrophic failures. Transmission and Distribution (T&D) companies therefore routinely specify the requirement for continuous winding temperature monitoring to optimize maintenance schedules and extend equipment lifetime.

One of the challenges, however, has been to find a cost-effective technology for high-voltage sensing applications. Various RF (radio frequency) wireless and IR (infrared) thermometer sensors have been used, but each has its deficiencies. The RF transmitter/receiver sensors suffer from the inherent noise & interference that exists in a high-voltage environment and can lose signal or show temperature spikes during switching operations that may lead to false alarms. Also, because these sensors use electronic components, their temperature range is typically limited to below 120°C for long-term use. Remote IR temperature sensors fare similarly because they require shielded electrical wiring and special mounting points with precise spatial alignment to the object surface being sensed. Infrared thermometers are known to report temperature shifts due to dust accumulation and emissivity changes caused by subtle surface corrosion. The reported temperature can be skewed by reflected infrared energy emitted by surrounding objects, and sudden changes in ambient temperatures can also introduce measurement error. 

RM fiber optic temperature sensors do not suffer any of the technical challenges associated with wireless and infrared thermometers. Fiber optic sensors can be routed directly to critical transformer monitoring points such as the windings. RM low-cost optical temperature sensors are rigidly attached to hot-spot locations and are completely immune to electromagnetic interference and noise bursts caused by high-voltage switching. RM fiber optic sensors are robust, can be manufactured to various lengths, and work like a conventional thermocouple. Best of all, each RM optical temperature sensor transmitter can monitor three phases providing both analog output and digital RS-485 Modbus RTU communication. RM fiber optic temperature probes are perfectly suited for smart grid dry type transformer temperature monitoring.


  • Most accurate hot spot measurement (better than IR camera and RTD)
  • Maintenance free Sensors and Monitors
  • Safe from Partial Discharge unlike RTDs
  • Peace of mind about getting sensor lenses cleaned and setting IR sensors
  • Most accurate heat run test with the same FO temperature sensors
Fiber Optic Temperature Monitoring for Dry Type Transformer (Cast Resin Transformer)


Fiber Optic Temperature Monitoring for Dry Type Transformer (Cast Resin Transformer)



Measurement Range-80 °C to +300 °C (cryogenic 4 °K range optional)
Measurement range (Optional Range extensions)Down to 4 °K / Up to +300 °C
Accuracy±1.0 °C (+/- 0.2 °C in relative temperature)
Number of Channels1 - 8 Channels
USB (to use with Rugged connect windows software)1 sec interval on USB / Micro SD card
Config portUSB (to use with Rugged connect windows software)


Temperature range-200 °C to +250 °C
Temperature range (Optional Range extensions) Down to 4 °K / Up to +300 °C
Repeatability0.2 °C
Accuracy absolute temperature+/- 0.8 °C
Accuracy relative temperature+/- 0.2 °C
Probe sheathing materialTeflon Coated, Rugged Polyimide protection for sensor tip
ConnectorStainless Alloy / Optional - Dielectric



Rugged connect provides remote visualization of temperature and other data being measured / monitored by various rugged monitoring systems. The software can connect to multiple monitoring devices for data collection and advance visualization. The intuitive user interface of the software is designed to give quick access to the most relevant information with highest level of data security.

  •  Cyber Security
  •  Real-time Data
  •  Data Logging
  •  Health Check


High Voltage Windings FO Temperature Sensors: 01 on each Phase (Total qty 03)FO Temperature Monitor: 04 Channel O201/T301 with Relays and Modbus/DNP3.0 (over serial)