Determining Oil Level in Oil-Filled Transformers With No Gauges
Written by Walt Powell, Professional Engineer
Sometimes an old substation will have old oil filled transformers that have no gauges. These are usually 500 kva to about 2000 kva transformers. We are not referring to pole top type transformers. Some Utilities used oil filled transformers with no accessories to save costs. They would consider these transformers to be small and basically disposal. Many of these substations have been sold by Utilities to the consumer. The consumer gets a cheaper primary rate and owns the substation, along with the responsibility to take care of it. Sometimes we are asked how to determine the oil level in a transformer that does not have an oil level gauge, without turning the transformer off. We safely feel the cooling tubes and the tank. If the tubes are cool and the tank is hot, it is low on oil. If the oil is properly circulating through the cooling tubes, the tubes will also be warm. Not as warm as the tank, but fairly close. Caution, only a qualified electrician or electrical engineer should do this. Stay away from energized parts and make sure the transformer tank is properly grounded before you touch it. Protect yourself from shock hazard and from an electrical arc blast hazard. This may well require PPE. Do not touch anything else while touching the transformer tank.
An infrared camera is an excellent way to do this and they are now very inexpensive. As long as the oil/silicone filled transformer is energized, you can get an accurate level.