Handheld Infrared Thermometers Can Be Divided into Three Categories
For faults of electrical equipment, thermal faults caused by current effects (conductive circuit faults) have heating power proportional to the square of the load current. For thermal faults caused by voltage effects (insulation medium faults), the heating power is proportional to the square of the operating voltage. Therefore, the operating voltage and load current of the equipment directly affect the effectiveness of infrared inspection and fault diagnosis. An increase in leakage current may cause uneven partial voltage distribution on high‑voltage equipment.
If the equipment runs with no load or at a very low load, the heat generated by equipment faults will be insignificant. Even severe faults may not appear in the form of characteristic thermal anomalies. Only when the equipment operates at rated voltage and under higher load will heat generation and temperature rise become more severe, and the characteristic thermal anomaly at the fault point will be more obvious.
Therefore, to obtain reliable inspection results during infrared testing, the equipment should operate at rated voltage and full load as much as possible. If continuous full‑load operation cannot be achieved, an operation plan shall be formulated to operate the equipment at full load for a period of time (e.g. 4 to 6 hours) before and during inspection. This provides sufficient heating time for faulty parts and ensures a stable temperature rise on the surface.
Since the criteria for fault judgment in infrared diagnosis of electrical equipment are usually based on the temperature rise at rated current, when the actual operating current during measurement is lower than the rated current, the on‑site measured temperature rise at the equipment fault point shall be converted to the temperature rise corresponding to rated current.
