Our standard processing technique for filtering transformer oil used in Oil Circuit Breakers and Tap Changers uses a 2 stage filter unit that is set up to process the oil through a .4 micron particle filter that has the ability to trap free and emulsified water. Our second stage uses a filter that removes dissolved moisture down to less than 5 PPM. The unit has oil heaters with low watt density to bring the oil temperature up in cold weather for improved flow and better dirt removal. In conjunction with this, we have an in line water monitor that gives us real time moisture levels as we are filtering. As you are aware, new oil from a sealed drum can have as much as 35ppm of dissolved water. An unsealed drum can contain much more water as a result of condensation during rapid ambient temperature changes while in storage. It is our practice to pre-filter all oil used in equipment. We also have an assortment of vacuum pumps for servicing transformers and SF6 equipment if the need arises.
The picture to the right shows our filter unit in the back of one of our trailers. The small housing on the right side is a .5 micron filter arrangement that we use for the initial drain downs to conserve the cost of the primary filters on the wagon.
The filter cart on the left has 2 outboard heaters that can be removed to allow the wagon to be wheeled through doorways into indoor substations. This is useful for servicing arc furnace transformers with integral tap changers. We are currently building another unit so we can deal with multiple pieces of equipment simultaneously and will provide us with redundant equipment in the event of a problem. The design and filtration levels will be the same.