What amount of free water can be detected by the dielectric breakdown strength test?

The dielectric breakdown strength test is a vital diagnostic tool used to assess the quality of insulating fluids, particularly in electrical equipment. It specifically measures the maximum voltage an insulating liquid can withstand before a breakdown occurs, indicating the presence of contaminants, including free water.

When it comes to free water content, the threshold for detecting it through this test is crucial. A level of 30 ppm (parts per million) or more is significant because it represents a point at which the moisture can have detrimental effects on the dielectric properties of the insulating fluid. At this level, the likelihood of electrical breakdown increases, leading to potential equipment failure or reduced operational efficiency.

In other words, 30 ppm is a critical concentration that signals caution, whereas lower concentrations might not have an immediate impact on dielectric strength to the same extent. Therefore, identifying the presence of free water at this level can guide maintenance decisions and intervention actions, ensuring the reliability and safety of the substation's operations.