Understanding liquid levels in your transformer
Transformer liquids provide dielectric strength and cooling for a transformer. A transformer is designed for the liquid to maintain dielectric protection against high voltages, but the optimal level must account for expansion and contraction based on temperature. As the temperature of the transformer goes up, the fluid expands. As the temperature of the oil goes down, it contracts.
As the liquid contracts to its lowest levels, it must sufficiently cover the active part of the transformer (the main core, windings, tap changer, and bushing terminals) and be high enough for the liquid to flow into the cooling radiators and recirculates via the bottom of the tank.
It is also essential that the transformer is not overfilled with liquid. At higher fluid temperatures, the oil expands and can fill the headspace until it overflows (in free-breathing units) or over-pressurizes the transformer (in sealed units). Liquid levels, tank pressures, and fluid temperatures must be monitored and set correctly. Liquid levels are measured with an installed level gauge—as shown in the video below. How you interpret the gauge data and cross-reference that information with the oil temperature can tell you if you need to top off your transformer with oil. SDMyers can assess the transformer and ensure the correct nitrogen pressure and vacuum level are applied and the liquid level is correct compared to the fluid temperature.
Watch and listen as Bob Rasor, Director of Transformer Services, explains the importance of liquid levels in more detail.
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June 24, 2022