TABLE OF CONTENTS | 1. | Why is the dew point of nitrogen in a transformer less than ?50 C? |
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| 2. | How would electrical faults occur? |
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| 3. | Why would the forces between the windings increase during a short circuit? |
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| 4. | How would a transformer fail? |
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| 5. | What is the upper moisture limit that should be specified when selecting a transformer? |
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| 6. | What are the most important tests for oil in a transformer? |
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| 7. | When would preventive maintenance be required for oil in a transformer? |
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| 8. | What are the methods of dealing with bad oil in a transformer? |
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| 9. | What are the causes of gas formation in the oil of a transformer? |
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| 10. | What is the purpose of the gas detector relay? |
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| 11. | How does the gas relay operate? |
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Answers
| 1. | Nitrogen is used in a transformer as a buffer gas between the oil and air. It separates outside air (containing water vapor) from the oil. Water vapor has devastating effects on the dielectric (insulation) strength of the oil. For example, one spoonful of water can reduce the dielectric strength of the oil in a large transformer by one-half. The dew point is the temperature at which the water vapor in the air starts to condense. It varies with the concentration of water vapor in the gas. For example, if the gas is very dry, its dew point will be around ?70 C. As the concentration of water vapor in the gas increases, its dew point will increase as well. |
