From which part of a transformer tank should a sample be drawn if the insulating fluid has a specific gravity less than 1?

The correct approach for drawing a sample of insulating fluid from a transformer tank when the fluid has a specific gravity of less than 1 is to take the sample from the bottom of the tank. This is because fluids with a specific gravity less than 1 are lighter than water and will naturally float on top of denser fluids, leading to a stratification where the most contaminated or degraded fluid may be found at the bottom.

Sampling from the bottom ensures that any sediment, debris, or lower-quality fluid that has settled there is captured, providing a more accurate representation of the overall condition of the insulating fluid. It also allows for the detection of potential issues like moisture ingress or contamination that may have accumulated at the base due to leaks or other failures.

In contrast, drawing samples from the top or middle of the tank may result in obtaining cleaner but potentially less indicative samples that do not reflect the true state of the fluid overall. Sampling from the side does not guarantee access to the most relevant areas of the tank for a comprehensive analysis either.