What sampling rules apply when collecting oil for a transformer test?

Sampling must avoid contamination, air ingress, and moisture pickup. Use clean, dry, dedicated sample bottles and tubing. Flush the sampling valve and lines first to remove stagnant oil. Collect a representative sample at steady flow without bubbles and cap immediately. Label with transformer ID, location, date, temperature, and sample point. For DGA, minimize agitation and headspace, and seal tightly to prevent gas loss. Wear gloves and keep containers out of rain and direct sun. Consistent sampling technique is essential for reliable trending.