Q: I’ve seen oil in sight glass, is this normal?

A: Sight glass type Oil Level Gauge usually installed in hermetically sealed transformer. Normally you don’t see any trapped oil inside the glass. If you do, most likely this happened due to shocks experienced by transformer during transportation through rough road or inappropriate handling during loading, transport or installation.

Sight glass doesn’t have rubber seal to prevent oil to move into the glass chamber, therefore oil might penetrate into the chamber if the transformer is tilted or shook hardly enough. If the red pointer in the sight glass is above oil, this is normal.

In a rare case, if the oil penetrated into the chamber and the red pointer is fall below oil, the level floating mechanism might failure and the oil level should be replaced with new one.