5 solutions for temperature monitoring of dry-type transformers

Dry-type transformer heating fault causes and key monitoring points

Dry-type transformer as the core hub of the distribution system, its insulation life depends directly on the operating temperature (every 6 ℃ rise, insulation life halved). In long-term operation, theIron loss (hysteresis loss and eddy current loss)respond in singingCopper loss (resistance loss)is the main heat source. In addition, nonlinear loads generatehigher harmonicIt will lead to skin effect and significantly increase the heating of the winding. If the heat dissipation is poor or long-term overload, it will lead to epoxy resin insulation aging, cracking, and even lead to turn-to-turn short-circuit and breakdown accidents.

To ensure the safe operation of the transformer, the following core areas must be precisely monitored:

• Low Voltage Winding (LV):Higher currents are the main heat generating component and the hottest point temperature is usually monitored.
• High Voltage Winding (HV):High voltage levels, which are difficult for traditional sensors to measure with direct contact, are difficult to monitor.
• Iron core:Prevents localized overheating due to multi-point grounding.
• Busbar connections:The connectors of the high and low voltage lead wires are susceptible to heat generation due to excessive contact resistance caused by looseness.

• Best recommended solution: fluorescent fiber optic temperature measurement technology

1. Fluorescent fiber optic temperature measurement technology (highly recommended)

For dry-type transformers with high voltage and strong magnetic field, fluorescent fiber optic temperature measurement is the only technology that can realize “direct temperature measurement of high-voltage windings”.

Technological Advantage:The fiber optic probe has extremely high insulation and resistance to electromagnetic interference. It can be pre-buried or installed directly on the surface of high-voltage windings (HV) and inside the duct, without worrying about creepage distance and insulation breakdown. Compared with traditional methods, it can capture the “hottest spot” inside the winding more realistically, and the data is not interfered by the leakage flux of the transformer, with zero drift in long-term operation.

2. Conventional PT100/PT1000 RTD temperature measurement

This is the current standard solution for dry-type transformers shipped from the factory and is usually pre-built inside the low-voltage windings.

Technical characteristics:The technology is mature and the cost is low. However, its sensor is a metal conductor, there are insulation hazards in high-voltage environments, and usually can only monitor the temperature of the low-voltage side. In addition, in the transformer startup or short-circuit impact, strong electromagnetic interference may lead to PT100 signal distortion or false alarm, and once the pre-buried sensor is damaged, it is extremely difficult to replace.

3. Infrared thermal imaging monitoring technology

Non-contact scanning of the transformer surface using an infrared thermal camera.

Technical characteristics:Ideal for monitoring the temperature of exposed transformer terminals, busbar connections and the enclosure. Its limitation is that it can not penetrate the epoxy resin casting layer, so it can not measure the real hot spot temperature inside the winding. Only as an auxiliary inspection means, can not replace the internal temperature measurement.

4. Wireless passive temperature measurement technology (RFID/SAW)

Transmission of temperature data via radio frequency signals, sensor mounted on terminal strip or surface.

Technical characteristics:It solves the problem of troublesome wiring and is suitable for the transformation of the external connection point of the old transformer. However, because the transformer itself is a huge source of electromagnetic interference, the wireless signal is very easy to be shielded or interfered with, resulting in unstable data transmission. And the sensor is large, can not be installed in the narrow winding airway.

5. Fiber Bragg Grating (FBG) temperature measurement technology

Measures temperature by using the change in wavelength of light, and has the insulating properties of an optical fiber.

Technical characteristics:Although resistant to electromagnetic interference, grating sensors are extremely sensitive to stress. The inherent mechanical vibration (50Hz/100Hz) that accompanies the operation of a dry-type transformer can easily cause the grating wavelength to drift, resulting in measurement errors. In addition, fiber optic gratings are brittle and can easily break in the complex installation environment of a transformer.

Performance Comparison of 5 Monitoring Programs for Dry-type Transformers

Conclusion and Selection Recommendations

For dry-type transformers, especially for 35kV and higher voltage levels or for data centers and railroad sites where the reliability of the power supply is required to be extremely high.Fluorescent fiber optic temperature measurement technologyIt is the best upgrade program to replace the traditional PT100. It not only solves the industry pain point that the high-voltage side can not directly measure temperature, but also ensures the accuracy of data in a strong electromagnetic environment.

For customized fiber optic temperature measurement solutions for dry-type transformers, please consult: Fuzhou Innotransformer.