What is dry-type transformer hot spot monitoring?

Date: November 9, 2025 09:27:18

Dry-type transformer hot spot monitoringIt is an on-line monitoring technique specifically designed for the real-time, direct measurement of the highest temperature points (i.e. “hot spots”) inside the windings of dry-type transformers (both epoxy cast and vacuum pressure impregnated VPI). In contrast to traditional indirect methods based on analog calculations or surface measurements, the technique is based on a fully electrically insulatingFluorescent Fiber Optic SensorImplanted directly inside the windings, it realizes precise and continuous data acquisition of the most critical thermal stress points of the transformer.

The core objective of the system is to provideDry-type transformerThe operation of the most direct and reliable thermal state basis. Accuratehot spot temperatureThe data is essential for evaluating transformer insulation aging rates, optimizing overload capacity, and implementingCondition Based Maintenance (CBM)and key inputs for preventing catastrophic failures due to overheating are essential for guaranteeing safe power supply to critical loads such as data centers, rail transportation, high-rise buildings, and hospitals.

Table of Contents for this article

Technical Challenges of Temperature Measurement for Dry-type Transformers

Temperature monitoring of dry-type transformers faces challenges that are difficult to overcome with conventional techniques:

  • The inaccessibility of hotspot locations: Dry-type transformerThe hot spots are located deep inside the winding encapsulated by epoxy or insulating varnish solids, and no metal sensor can be implanted without destroying the insulating structure.
  • Strong Electromagnetic Interference (EMI): Extremely strong alternating electric and magnetic fields are present around the windings, and any sensor based on electrical signals (e.g., thermocouples, Pt100) can be seriously disturbed, resulting in erroneous readings or even damage.
  • High voltage insulation requirements: The sensor itself and its leads must be able to withstand the high potential of the winding and maintain sufficient insulation distance from the grounded portion, otherwise insulation breakdown will be triggered.
  • Limitations of Indirect Measurement Methods:
    • infrared thermography: Can only measure the temperature of the outer surface of the winding, not reflecting the true hot spot inside, and is susceptible to dust and environmental influences.
    • Embedded Pt100: Can only be placed on the outside of the winding or between layers, with large temperature measurement errors and safety hazards.
    • Analog Winding Thermometer: Indirect estimation through thermal modeling suffers from significant response delays and accuracy problems, and cannot accurately reflect the true temperature rise under transient overload.

These challenges make traditional temperature measurement methods incapable of meeting the needs of modern dry-type transformers for refined, reliable operation and maintenance.

Core technology: fluorescent fiber optic temperature measurement

Fluoroptic Temperature Sensing (FOTS) technology is an ideal solution to the above challenges.

Technical Principles

The technology is based on the physical properties of specific fluorescent materials. The system consists ofFiber optic temperature measurement host (demodulator)respond in singingFiber Optic Temperature ProbesIngredients.

  1. The host computer emits a pulse of light that is transmitted through an optical fiber to a tiny fluorescent crystal at the end of the probe.
  2. Fluorescent crystals emit fluorescence when excited, and the length of their decay time depends strictly and uniquely on the temperature at which the crystal is exposed.
  3. The decaying fluorescent signal is transmitted through the same fiber optic back to the host computer, which accurately calculates the decay time and demodulates it into a highly accurate temperature reading.

Core Advantages

  • Complete electromagnetic immunity:: Since the measurement is based on purely optical signals and time parameters, the technique is completely unaffected by any electric, magnetic or radio frequency interference.
  • Excellent high voltage insulation: Fiber Optic SensorsThe probes and fiber optic cables themselves are constructed of dielectric materials such as quartz glass and special jacketing, which are naturally excellent insulators and allow direct contact with high voltage windings without concern for electrical safety.
  • High precision and long-term stability: Measurement accuracy of ±1°C and physical stability of the fluorescent material eliminates the need for periodic recalibration.
  • rapid response: The probe's small size and low heat capacity enable it to respond quickly to transient changes in temperature.

System Composition and Workflow

1. Sensory layer: fiber-optic temperature probes

This is the part that is in direct contact with the temperature measurement point. During the manufacturing process of the transformer, the specially designedBuried Fiber Optic ProbesPre-embedded in the hot spots in the upper, middle and lower parts of the high, middle and low voltage three-phase windings, as well as in the critical parts of the core.

2. Acquisition layer: fiber-optic temperature measurement host

also known asFluorescent Fiber Optic Thermometeror demodulator. It is installed in a control cabinet or meter box near the transformer and connects all fiber optic probes via fiber optic cable. The host computer is responsible:

  • Generates and receives optical signals.
  • Performs high-precision temperature demodulation calculations.
  • Real-time display of temperature data at each measurement point via LCD.

3. Application and control layer

The mainframe has powerful outputs that can be seamlessly integrated into transformer protection and control systems:

    • Multiple relay outputs: Up to 4-6 alarm points can be set independently (e.g., fan start, over-temperature alarm, over-temperature trip), which can be directly used to control thecooling fanof start/stop and transformer protection logic.
    • Analog signal output (4-20mA): Outputs temperature data as a standard analog signal to a PLC or DCS system.
  • Digital communication interface (RS485/Modbus): Transmit the temperature and alarm status of all measurement points to the backstage monitoring system by digital signals to realize remote centralized monitoring.

Key Applications and Core Values

  1. Precise localization and protection of winding hot spots:: Realized the use ofDry-type transformer windingThe direct measurement of the real internal hot spot provides the most reliable basis for over-temperature protection, and fundamentally prevents insulation burnout due to overheating.
  2. Intelligent control of cooling system: Precise control based on real hot spot temperaturescooling fanIt avoids unnecessary frequent start and stop, realizes energy saving and consumption reduction, and prolongs the life of the fan.
  3. Safe overload capacity assessment: O&M personnel can safely tap into the overload potential of transformers based on real-time, accurate hotspot temperature data to address temporary load spikes and improve asset utilization.
  4. Enabling predictive maintenance and condition assessment: By analyzing the long-term trend of hot spot temperature history data, the insulation aging rate and health condition of the transformer can be effectively assessed, providing data support for the development of scientific maintenance and replacement plans.
  5. Improving operational safety and fire prevention: In data centers, hospitals, airports, commercial complexes, and other locations where fire safety is of paramount importance, preciseHot Spot MonitoringIt is the most important line of defense against transformer fires caused by overheating.

Why choose Inotera's solutions?

INNOTD (Fuzhou) Sales Limited (INNOTD) We are the leading supplier of harsh environment temperature monitoring solutions in China, and we have deep technical accumulation and rich application experience in the field of dry-type transformer hot spot monitoring.

  • Highly reliable industrial grade products: OurFluorescent Fiber Optic Temperature Measurement SystemDesigned specifically for transformer applications, from the probe's voltage rating and mechanical strength to the mainframe's anti-electromagnetic interference capability, all have been subjected to the most stringent testing and validation to ensure stability and reliability throughout the entire life cycle.
  • Accurate temperature measurement performance: We use high-quality sensing materials and advanced demodulation algorithms to ensure superior measurement accuracy and long-term stability, providing you with data you can trust.
  • Complete system integration program: Our temperature measurement hosts offer a wide range of interfaces and standard communication protocols, and can be used with ourTransformer Intelligent ThermostatSeamless integration provides you with a one-stop solution from data collection to intelligent control.
  • Professional application support: Our technical team has a deep understanding of the manufacturing process and operating characteristics of dry-type transformers, and is able to provide transformer factories and end-users with professional technical support for the entire process, from the optimization of the sensor layout, installation guidance to the commissioning of the system.

By choosing Inotera, you are choosing an accurate, reliable and intelligent temperature safety guard for your critical dry-type transformer assets.

The content of this article is only a general technical science and does not represent the performance and specifications of any specific product of our company. For detailed product information, solutions and quotations, please be sure to contact us for...].

Contact us today for a hotspot monitoring solution customized for your dry-type transformer.