Other Tests
We now briefly elaborate some other tests that are commonly conducted on transformers. These involve temperature rise test, drying out of transformer, and open circuit and Sumpner's test.
1 Temperature rise test is performed to measure the temperature increase of the major and conservator tanks. The transformer passes the test if the rise is inside the specified limits given through the manufacturer.
2 Drying out of transformer is essential if
- Tests imply the presence of moisture in transformer oil;
- A oil does not withstand the dielectric strength test; and
- An insulation resistance readings are not satisfactory.
Box 3: Method of Drying Out the Transformer
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Normally HOT OIL CIRCULATION technique should be used for drying out the distribution transformer. In special circumstances, where this technique does not provide satisfactory results, SHORT CIRCUIT WITH HOT OIL CIRCULATION should be used. In this technique, both core and winding inside the tank are concurrently dried out/streamlined with filter. The moisture dries out from the windings into the oil and is removed from the oil by evaporation and filtering.
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