What causes water contamination in transformers, commonly found in indoor tanks?

Water contamination in transformers, particularly those housed in indoor tanks, is predominantly caused by condensation due to temperature fluctuations. As temperatures drop, moisture in the air can condense on cooler surfaces, including the walls of the transformer tank. This accumulated moisture can then mix with the insulating oil, leading to water contamination.

Condensation is especially prevalent in environments where transformers experience significant thermal cycles. For instance, transformers may heat up during operation and then cool down when idle, creating the ideal conditions for moisture in the air to condense inside the tank. This water contamination can deteriorate the insulating properties of the oil, increase the risk of corrosion, and potentially lead to transformer failures.

Other factors, such as overheating, incorrect oil levels, or electrical arcing, may influence the operational efficiency or long-term durability of a transformer, but they do not primarily lead to water contamination in the same way that condensation does.