In order to help readers better understand the application of infrared diagnosis in electrical equipment, several typical examples are provided below.
**Example 15-1: Generator and Motor**
1. The stator windings of generators and motors can be inspected using either the applied current method or direct shutdown detection. Thermal spectrum recording and analysis are performed on all winding joints. For instance, out of 75 measurement points on a hydro-generator’s stator winding, 72 were continuously distributed between 42.5°C and 62.5°C (with a detection current of 0.68 Ie). Two of these points showed higher temperatures—72.5°C and 95.8°C. The former was classified as a general defect, while the latter was considered a major defect. Upon disassembling the joints with major defects, it was found that two of the six welds had poor quality, with resistance 18.4 times higher than normal (see Figure 15-2).
2. The maximum temperature rise of the stator teeth was measured at 26.2K, and the maximum temperature difference between the teeth reached 17.1K, which exceeded the requirements of 25K and 15K specified by the Pre-Regulation.
3. An infrared camera was used to measure the temperature of a generator's brush. One brush was found to have a temperature above 150°C, exceeding the standards set by GB/T 7064 and GB 755. According to regulations, the temperature rise should not exceed 80K, and if it does, the temperature distribution must be uniform. A brush with a temperature rise more than 30K above the average is considered unqualified. The issue was traced back to improper contact pressure adjustment.
**Example 15-2: Transformer**
1. During an infrared inspection of a main transformer, an abnormality was detected in the general arm of phase A. Further checks revealed that the cap screw was not tightened properly, preventing a potential accident (see Figure 15-3).
2. In a 110kV substation, an infrared thermometer was used to measure the temperature of the outlet wall bushings. While phases A and B showed normal temperatures (27°C), phase C reached as high as 170°C. This early detection allowed for timely elimination of the hidden danger.
3. The low-voltage side lead connector of a distribution transformer was measured at 114°C, which is 24 times higher than the allowed 90°C. Upon investigation, it was found that the joint had poor contact.
**Example 15-3: Circuit Breaker and Disconnector**
1. A 6kV circuit breaker in a substation was inspected using an infrared thermometer. The temperature of the B-phase contact housing was recorded at 45.8°C, indicating poor internal contact. After one week, the temperature rose to 70.9°C, signaling a severe overheating failure. Maintenance revealed a contact resistance of 8.09mΩ, significantly higher than the normal value of less than 90μΩ. After repairs, the contact resistance dropped to 53μΩ, and the temperature returned to normal.
2. During an infrared inspection of a SW2-220II type circuit breaker, the temperature of the upper cap of the A-phase south column was measured at 87°C, with a temperature rise of 70°C. This was much higher than the normal temperature of 19°C. Despite the operating current being only about 1/3 of the rated value, the contact resistance was found to be 52 times higher than the normal phase. Inspection revealed ablation on the contact surface between the support seat and the static contact.
3. An infrared camera was used to measure the temperature of a high-voltage isolating switch. The blade temperature was recorded at 150°C, which exceeded the maximum allowable temperature (see Figure 15-4).
**Example 15-5: Cable**
The temperature of a 30kV cable head was measured at 125°C using an infrared thermometer. After shutdown, it was discovered that the cable head had discharge marks due to poor sealing. Once the cable head was re-made, the temperature returned to normal.
**Example 15-6: Voltage-Induced Device**
1. A 220kV lightning arrester was inspected using an infrared camera. The thermal field showed uneven distribution, with a high temperature in the center and lower temperatures at both ends. The temperature difference was 7.06°C. Live testing showed an increase in leakage current from 560μA to 756μA within a day, prompting an emergency shutdown. Insulation resistance had dropped to 15 MΩ, indicating severe moisture inside the arrester.
2. An infrared thermometer was used to measure the temperature of a 220kV capacitance-type voltage transformer. The C-phase upper capacitor porcelain sleeve showed local overheating, with a hot spot temperature of 16°C and ambient temperature of 2°C. Power-off inspection revealed a tanδ of 6.45%, far beyond the acceptable limit. Disassembly showed a broken copper strip from the inner core to the lead end, along with overheated and blackened insulating oil.
3. A substation line combined with a capacitor was inspected using an infrared thermometer. The upper phase of the B-phase was severely overheated, reaching 41°C, compared to 32°C for the normal phase. The phase difference was 9°C, and the tanδ was 10 times higher than normal.
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