**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. This ensures that potential thermal issues in equipment are identified early, allowing for timely maintenance and preventing failures.
**II. Key Test Objects**
The primary objects of infrared detection include secondary equipment and critical parts within the secondary circuit. These components are essential for the safe and stable operation of power systems.
- **TA Loop**
- Terminal boxes, protection screens, and test terminals often suffer from loose connections or rust, leading to poor contact and overheating.
- Measurement and control screens, as well as metering screens, also require attention due to similar issues.
- **DC Screens, Protection Panels, and Control Units**
- DC air switches and fuses are common points of failure, typically due to loosening and subsequent heat generation.
- **AC and DC Circuits, Battery (Including Communication DC System)**
- The DC bus terminal blocks can experience overheating, especially if there are poor connections.
- **TV Loop**
- Grounding points and fuses in the station TV loop may cause heating due to small wire diameters or poor contact.
- **Secondary Circuit and Equipment**
- Terminal blocks and protection device components, such as plug-ins, are vulnerable to poor contact, particularly in power and AC modules.
- **Other Secondary Circuits**
- Energy storage circuits in circuit breakers and control box secondary circuits may show heating at relay contacts.
**III. Testing Environment Requirements**
- The equipment being tested must be live. Ensure safety while opening any covers that block infrared radiation, such as windows or panels.
- Ambient temperature should not be below 5°C, and humidity should remain under 85%. Avoid testing during rain, snow, fog, or high winds. Wind speed should generally not exceed 0.5 m/s.
- Outdoor testing is best done before sunrise, after sunset, or on cloudy days. Ensure the device is not exposed to direct light.
- For current-heating equipment, testing should occur under peak load conditions, ideally with a load of at least 30% of the rated capacity.
**IV. Detection and Diagnosis Cycle**
- The frequency of infrared inspections depends on factors like importance, load rate, and environmental conditions.
- Normally, secondary equipment such as TA circuits, protective power switches, and DC systems should be tested annually.
- Important substations or those with aging equipment may require more frequent checks.
- After new installations, expansions, or major overhauls, infrared detection should be performed within 24 hours of load.
**V. On-Site Operation Methods**
- Before starting, calibrate the infrared camera internally and ensure the image stabilizes.
- Scan all areas first to identify abnormal thermal patterns, then focus on specific hotspots.
- The emissivity of secondary equipment should be set between 0.78 and 0.9.
- Ensure the equipment fills the entire field of view while maintaining a safe distance.
- Set multiple angles in advance to maintain consistency in future tests, improving efficiency.
- Record key parameters like load current, voltage, and ambient temperature for accurate analysis.
**VI. Diagnostic Methods and Judgment Criteria**
- **Surface Temperature Judgment**
Based on measured surface temperatures, compare against GB 763-1990 standards. Exceeding limits may indicate serious defects, especially under low load or high mechanical stress.
- **Similar Comparison Method**
Compare temperature differences among three-phase devices. If asymmetry exists, consider load effects. Voltage-heating devices should be judged based on allowable temperature differences.
- **Relative Temperature Difference Method**
For current-heating devices, use relative temperature difference calculations (DL/T 644-1999). If the difference is less than 10K, further inspection is needed.
- **Thermal Spectrum Analysis**
Analyze thermal patterns to determine whether the device is functioning normally or has an anomaly.
- **Judgment Basis**
- **Emergency Defect (I):** Surface temperature >70°C, temperature rise >30°C, or relative temperature difference >10°C.
- **Major Defect (II):** Surface temperature >60°C, temperature rise >20°C, or relative temperature difference 5–10°C.
- **General Thermal Defect (III):** Surface temperature >50°C, temperature rise >10°C, or relative temperature difference <5°C.
- **Low Temperature Rise (<10°C):** Monitor closely, especially under small loads, and assess heat changes caused by load variations. Voltage-induced defects are usually classified as major or above.
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