The document discusses on-load tap changer filter systems, which are used to filter insulating oil in tap changers of power transformers. It describes how arcing in tap changers produces contaminants that degrade the oil over time. The Allen Tap Changer Filter System is highlighted as a self-contained automatic filtering system that removes solids, moisture, and gases from tap changer oil on a continuous basis to keep it clean. The system utilizes pumps, filters, heaters and other components enclosed in a weatherproof cabinet to maintain optimal dielectric properties in the tap changer tank.