**I. Management Regulations**
According to the GDW 168-2008 "Power Transmission and Transformation State Inspection Test Procedures," infrared temperature measurement is conducted on a regular basis to ensure the safe and stable operation of power equipment. This practice helps identify potential thermal faults early, preventing unexpected failures and improving overall system reliability.
**II. Key Test Objects**
The main components that require infrared detection include secondary equipment and critical parts of the secondary circuit. These include:
- **TA Loop**:
- Terminal boxes, protection panels, and test terminals may suffer from loose connections or rust, leading to poor contact and overheating.
- Measurement and control panels also need inspection for similar issues.
- **DC Screens and Control Panels**:
- DC air switches and fuses should be checked regularly for looseness, which can cause poor contact and heat buildup.
- **AC and DC Circuits**:
- The battery (including communication DC systems) and DC bus terminal blocks are key areas to monitor for abnormal heating.
- **TV Loop**:
- Grounding points, circuit breakers, or fuses in the station TV loop may experience poor contact, leading to overheating.
- **Secondary Circuits and Equipment**:
- Terminal blocks, protection device bodies, and plug-ins are vulnerable to poor contact, especially in power and AC modules.
- **Other Secondary Circuits**:
- Circuit breaker mechanism energy storage circuits and control box secondary circuits may show signs of heating due to loose terminals or relay contacts.
**III. Testing Environment Requirements**
To ensure accurate results, the following conditions must be met during infrared testing:
- The equipment being tested should be live and operational. Ensure safety while removing any obstructions like glass windows or covers that may block infrared radiation.
- Ambient temperature should not be below 5°C, and humidity should not exceed 85%. Avoid testing during rain, fog, snow, or high wind speeds (above 0.5 m/s). If wind is strong, record it and adjust measurements accordingly.
- Outdoor testing is best done before sunrise, after sunset, or on cloudy days. Ensure the device under test is not exposed to direct light or reflections.
- For current-heating equipment, testing should occur under peak load conditions, ideally at least 30% of the rated load.
**IV. Detection and Diagnosis Cycle**
The frequency of infrared inspections depends on factors such as the equipment's importance, load level, and environmental conditions. Normally, secondary equipment like TA circuits, protective power switches, and DC systems should be inspected once a year. In critical substations or those with aging equipment, the inspection interval may be shortened. After new installations, expansions, or major overhauls, infrared testing should be performed within 24 hours of commissioning.
**V. On-Site Operation Methods**
- Turn on the infrared camera and perform internal temperature calibration. Wait for the image to stabilize before starting.
- Scan all test areas first to identify any abnormal thermal patterns, then focus on specific hotspots and critical components.
- The emissivity of secondary equipment is typically between 0.78 and 0.9.
- Maintain a safe distance and ensure the equipment fills the camera’s field of view.
- Plan multiple angles in advance for accurate and repeatable measurements. Mark positions for consistency in future tests.
- Record key parameters such as actual load current, voltage, equipment temperature, and ambient reference temperatures.
**VI. Diagnostic Methods and Judgment Criteria**
- **Surface Temperature Judgment**: Based on GB 763-1990, if the surface temperature exceeds standard limits, assess the severity based on load, importance, and mechanical stress.
- **Similar Comparison Method**: Compare temperature differences between phases or similar devices in the same circuit. A difference exceeding 30% of allowable values may indicate a serious defect.
- **Relative Temperature Difference Method**: For current-heated devices, measure the relative temperature difference using DL/T 644-1999 guidelines. If the temperature rise is less than 10K, further analysis is needed.
- **Thermal Spectrum Analysis**: Analyze the thermal pattern of the device in normal and abnormal states to determine its condition.
- **Judgment Basis**:
- Emergency Defect (I): Surface temperature >70°C, or temperature rise >30°C, or relative temperature difference >10°C.
- Major Defect (II): Surface temperature >60°C, or temperature rise >20°C, or relative temperature difference 5–10°C.
- General Thermal Defect (III): Surface temperature >50°C, or temperature rise >10°C, or relative temperature difference <5°C.
- If the temperature rise is <10°C, record it and monitor closely. Voltage-induced defects are generally considered major or above.
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