If a transformer breaker trips with bucholz relay action, the transformer should not be charged before conducting detailed investigation. The high voltage and low voltage sides of the transformer should be isolated. DC supply to and from Bucholz relay is also to be isolated. The gas collected in the Bucholz relay has to be tested as detailed below.
- Examine Bucholz relay.
- Note and record the quality and colour of gas collected. A colour less accumulation usually indicates the presence of air.
- Release a small quantity of gas and smell. Peculiar smell other than oil smell is not desirable.
- Prepare silver nitrate solution of any concentration in a oil bottle (the solution must be clear).
- Allow some quantity of gas to bubble through this clear solution of silver nitrate.
- If there is no change in the colour of the solution, it generally indicates that the gas is merely air. Whitish precipitation-decomposition of paper. Yellow precipitation-decomposition of wood. deep grey-gas of over heated oil due to burning of iron. Black-gas of decomposed oil due to electric arc.
- If a precipitate is obtained, thorough examination of the transformer should be made at the earliest opportunity.
Source: Engineers Diary 2003