It is not recommended to take an oil sample for hermetically sealed oil distribution transformers since the transformer itself is fully closed to the environmental condition. It is not recommended to do it before the first 5 years under operation. In case a short-circuit failure or another malfunction happens inside the transformer, than an oil sample can be taken. An important point needs to be taken into account is the ambient temperature at the site during taking the oil sample. Due to the fact that, the oil is initially filled in the factory around 20°C; it's recommended that the user to take the oil sample at minimum 20°C for the hermetically sealed ODT transformers. If the ambient temperature is lower than 20°C then please contact with Schneider.
