The routine inspection and periodic inspection of instrument transformers and secondary circuits should be conducted annually. For equipment such as unattended substations where routine inspection is not possible, periodic inspection becomes even more important. Additionally, long-term accumulated inspection data serves as important reference material for making judgments.
1. Visual Inspection Same as routine inspection.
2. Measuring Insulation Resistance The insulation resistance of the equipment itself and the secondary circuit should be measured separately. The judgment criteria for the insulation resistance of the equipment itself vary depending on the equipment structure and the primary and secondary circuits, and are also affected by external environmental factors such as temperature and dust accumulation. Therefore, it is insufficient to judge solely based on standard resistance values. It is better to make the following judgments based on measurement data:
(1) Use the standard insulation resistance value as a rough target.
(2) While recording the resistance values from periodic measurements, also note the temperature and humidity, and ensure that these two values do not show a significant decrease compared to previous measurements.
(3) The measured values should be compared with those of other equipment of the same model measured at the same location and time, and there should be no significant differences.
(4) Clean the porcelain tubes, insulating bushings, terminal blocks, and other parts thoroughly and meet certain requirements before measurement.
Under the above conditions, if an abnormality in insulation resistance is confirmed, it is likely that insulation aging has occurred. Therefore, the insulation aging can be determined by measuring tanδ and other parameters.
3. Measurement of tanδ Measuring dielectric loss is a method to judge the degree of insulation aging and moisture absorption.
Periodic measurement and recording of tanδ are useful for judging insulation aging, but since tanδ varies with temperature and also differs with different measuring instruments, it is necessary to use the same instrument for measurement and convert to the same temperature. When measuring tanδ, judgments are made by measuring the voltage characteristics of tanδ.
