How is a transformer oil sample collected without contamination?

Sampling uses clean, dry tools, correct flushing, and sealed containers. The sampling valve is cleaned, then flushed to remove stagnant oil and debris. The sample is collected slowly to avoid aeration and bubbles. For DGA, bottles are filled carefully with minimal headspace and sealed immediately. Labels record transformer ID, date, temperature, and sampling point. Samples are transported upright and protected from heat and sunlight. Clean technique is essential because moisture, air, or particles can distort results.