When the breakdown voltage of the porcelain insulator's operating frequency is lower than the flashover voltage, it is considered a low-quality insulator. Damaged porcelain insulators are called zero insulators. According to DL/T626-2015 'Quality Inspection Regulations for Hanging Ceramic Insulators':

When the voltage level is above 500kV and the insulation resistance of the insulator is less than 500mol, it is classified as a degraded insulator. When the voltage level is below 500kV and the insulation resistance of the insulator is less than 300m, it is considered a degraded insulator.

Degraded insulators with insulation resistance greater than 10m are usually called low insulation, while those with resistance below 10m are called zero insulation.

The two main reasons for low zero values of ceramic insulators are as follows:

First, some batches have high insulator degradation rates, and strict inspection was not conducted during the initial production stage, resulting in defective products.

In addition, due to long-term effects such as electromechanical loads, sunlight, and temperature changes, Ceramic insulators can also experience faults such as decreased insulation resistance, cracks, and perforations.

When the porcelain insulator is zero, the probability of foul flashover occurs when the insulator is overcurrent, even under normal operating voltage. During insulator series flashover, short-circuit current passes through the internal gap of the zero insulator. The thermal effect of high current will cause

resulting in a series of serious accidents, such as ceramic component breakage, head plate breakage, casting breakage, steel leg detachment, and ceramic head firing into glass.

Compared to high-quality insulators, zero-porcelain insulators have different electrical characteristics, partial discharge, and temperature distribution. Based on these characteristics and differences, appropriate instruments or equipment can be used for various measurements. The voltage distribution method (spark fork method) is currently the most common method in China

The detection methods for internal and external zero-value ceramic insulators use infrared thermal imaging technology and insulation resistance measurement.

Voltage Distribution Measurement Method (Spark Splitting Method): When there are zero-value insulators in the insulator string, the voltage distribution of the insulator string is greatly affected. A fork made of metal wire is installed at the end of the spark fork, so that one end of the fork contacts the insulator under the insulator

Edged steel cap. If the other end is close to the steel cover plate of the insulator being tested, sparks will be generated in the gap between the steel caps. The higher the distributed voltage of the insulator being tested, the earlier the spark is generated, and the louder the spark sound. The insulation under test can be determined based on the discharge situation

The voltage of the sub-unit. If the insulator being tested is zero, it is not affected by voltage, so there is no spark.

Method for measuring leakage current: Generally, the leakage current in ceramic insulator strings is at the milliampere level. When the insulator is present, the leakage current value increases over time. Currently, current sensors for measuring leakage current have no issues with measurement accuracy, but under normal conditions, leakage current is not a problem

Values change over time and with the environment, so there are still issues.

Infrared imaging technology: The principle behind infrared thermal imaging to detect degraded insulators is to make them appear bright (low) or dark (zero) based on their thermal imaging characteristics. If the temperature distribution in the insulator string is discontinuous and there is a bright (or dark) thermal image, it is judged to be low (or zero).

insulator. Methods for measuring insulation resistance: mainly composed of an insulating wrench meter and an electronic insulation resistance meter. Zero overload directly measures insulation resistance with a resistance meter to check for zero insulation. Using an insulation resistance meter to detect zero or low value insulators is very accurate. But because of the single

The test time is relatively long, with the resistance value of each ceramic insulator taking at least 1 minute or more, making it unsuitable for large-scale insulator testing. Additionally, due to the relatively low detection voltage, defects in large-tonnage insulators are difficult to detect.