A "transformer insulation resistance measurement" is a diagnostic test used to assess the condition of the insulation system within a power transformer. It is commonly performed during routine maintenance or as part of a diagnostic assessment to detect possible issues, including moisture ingress.
The insulation system in a power transformer is designed to prevent the flow of electric current between conducting parts. It is crucial for the proper functioning and reliability of the transformer. However, over time, the insulation can deteriorate due to various factors, including moisture ingress.
Moisture ingress is a significant concern because it can lead to insulation breakdown and other related problems. When moisture is present in the insulation, it can lower the insulation's resistance, making it easier for current to flow through the insulation. This condition is known as a decrease in insulation resistance or an increase in leakage current.
To detect moisture ingress in a power transformer, the insulation resistance measurement technique is employed. Here's how it works:
Test Setup: The transformer is isolated from the system and disconnected from its power supply. It is essential to ensure that all connections to the transformer are removed during the test.
Applying a Test Voltage: A voltage is applied across the insulation system of the transformer. The test voltage is usually DC (direct current) and can be generated using specialized equipment.
Measuring Current: The current flowing through the insulation system is measured. This current is referred to as leakage current.
Calculating Insulation Resistance: The insulation resistance is calculated using Ohm's Law, which states that resistance (R) is equal to voltage (V) divided by current (I). Mathematically, R = V / I.
Analyzing the Results: The measured insulation resistance value is compared with historical data or acceptable limits. If the insulation resistance is lower than expected, it indicates a potential issue with the insulation, which could be due to moisture ingress or other problems.
If the insulation resistance is significantly decreased, it suggests that moisture might have entered the insulation system, reducing its ability to insulate effectively. The presence of moisture can cause further degradation, leading to a higher risk of transformer failure and costly repairs.
In summary, a transformer insulation resistance measurement detects moisture ingress by measuring the leakage current and determining the insulation resistance. A decrease in insulation resistance indicates possible moisture-related issues, prompting further investigation and remedial actions to maintain the transformer's reliability and performance.