Study of Fire Behavior of Electrical Current Insulators for Overhead Lines in Railroad Tunnels
Researching Fire Development and Fire Growth with Infrared Cameras in Burning Environment
Challenge
Fire testing overhead lines and insulators involves measuring temperature gradients and heat-induced expansions accurately despite dense smoke, intense heat, and the lack of established reference values. Ensuring visibility, measurement precision, and sensor reliability within a 40-50 minute exposure period under extreme fire conditions presents significant practical challenges.
Solution
Infrared cameras strategically positioned at varying distances and heights precisely monitor temperature distribution on overhead lines and insulators throughout the fire scenario. Complementary thermocouples and tensile force sensors validate temperature data, ensuring robust and accurate measurement results despite unexpected smoke generation and elevated ambient temperatures.
Benefits
- Continuous, reliable temperature measurement despite heavy smoke, enabling accurate heat resistance evaluation.
- Early identification of component failure points enhances preventive safety measures.
- Real-time data correlation with mechanical stress measurements increases overall test reliability.
- Rapid and precise evaluation of overhead line integrity facilitates efficient infrastructure optimization.
- Unified data management simplifies comprehensive analysis and accelerates improvements for future fire scenarios.
Evaluating Heat Resistance of Overhead Lines and Insulators in Fire Tests
Emerging fires in train traffic can pose a considerable safety risk. Fire tests are carried out in test tracks or tunnels to better prepare for such scenarios and improve the infrastructure. In one of these tests, for example, the resistance of overhead lines and electrical current insulators to the effects of heat is determined. The aim is to test how long the power supply to the locomotive and carriages (e.g., for air conditioning and ventilation systems) can be maintained. These tests are crucial to ensure the safety and reliability of rail operations under extreme conditions.
For this purpose, a realistic model of a railroad carriage is ignited with a burning liquid. The temperatures of the overhead line (aluminum) and the current insulators (silicone/ceramic) are recorded at various points. Not only are point measurements carried out, but temperature gradients of the components are also determined. At the same time, the effect of heat on the expansion of the overhead line and, thus, on the tractive force is being investigated. One potential problem could be the smoke generated by the burning liquid, which could significantly impair visibility and temperature measurements. Measuring instruments and infrared cameras must be protected and calibrated accordingly to provide accurate data.
The target temperatures on the overhead line and current insulators often need to be specified, which poses additional challenges when planning and carrying out the test. There are no reference values or previous fire tests in some test scenarios, so these tests are carried out for the first time with various measuring systems. The maximum ambient temperature of the measuring systems in an example test is 40 °C to 50 °C (104 °F to 122 °F). The entire fire test is designed to last 40 to 50 minutes. The results of this test will be decisive for future safety measures and which technical specifications need to be developed for the use of overhead lines and current insulators in tunnels.
Optris Infrared Cameras Maintain Operation in Fire Conditions
To meet all the requirements in the sample test, a PI 640i with a 33 x 25 lens and a PI 1M with a 41 x 25 lens were installed. The PI 1M with a distance of approx. 10 m, at a height of 60 cm, and the Pi 640i with a distance of approx. 15 m, at a height of 3.5 m.
In addition, the distributor Schotec AG installed various thermocouples and tensile force sensors on the fire model to compare all measured values and check their plausibility. All sensors and IR cameras were recorded using DeWeSoft and documented with a time stamp. This was possible thanks to the DeWeSoft plug-in for the Optris PIX Connect software, which was easy to install. This test showed unexpected smoke development and an increased ambient temperature. Within 15 minutes, these two factors arose in the tunnel, causing the overhead line and the current insulators to melt away. The test tunnel had to be evacuated. The fire department, which was already on site, then extinguished the fire.
The PI 640i, which was still intact and survived the fire, precisely recorded all the temperatures that occurred in the visible area throughout the entire time (including during the fire extinguishing process). These were between room temperature at the beginning and close to 900 °C (1652 °F) shortly before the fire was extinguished.
Superior Performance in Extreme Conditions and Easy Data Integration via DeWeSoft PlugIn
The PI 640i provides an outstanding price-performance ratio, featuring a high resolution in the 8 – 14 µm infrared range. This specific wavelength enabled precise measurements even through unexpectedly dense smoke, allowing continuous temperature recording documented alongside other sensor data using the DeWeSoft PlugIn.
The four interchangeable lenses offer adaptability for future experiments, allowing for both long-distance imaging and detailed close-ups with the wide-angle lens. A water-cooling housing with an air purge attachment is available for all lenses, enabling the infrared camera to operate at ambient temperatures up to 315 °C (599 °F). The integrated air purge unit prevents condensation and effectively removes dirt from the camera lens.
With a thermal sensitivity of just 40mK, the PI 640i is also highly advantageous for future tests on current insulators at much lower temperatures, planned up to 100 °C (212 °F), as it can accurately display temperature gradients on the insulator.
The seamless integration with DeWeSoft software allows for the combination of various measuring systems on a single platform, facilitating comprehensive and efficient data collection for future tests.
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