The Transformer Oil Resistivity Test measures the electrical resistance of insulating oil under specific temperature conditions. Electrical resistivity is a critical parameter that indicates the oil’s ability to resist leakage current and maintain effective insulation within a transformer.
High resistivity reflects good insulating properties, while low resistivity may indicate contamination, moisture presence, oxidation by-products, or ageing of the oil.
Importance of Resistivity Testing
Transformer oil performs two essential functions:
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Electrical insulation
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Heat dissipation
Low resistivity can lead to:
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Increased dielectric losses
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Higher dissipation factor (tan delta)
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Reduced insulation performance
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Risk of partial discharge
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Accelerated ageing of solid insulation
Resistivity testing helps assess oil condition and detect early deterioration before major failures occur.
When is the Test Recommended?
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During routine condition monitoring
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After oil filtration or reclamation
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When tan delta values are high
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During commissioning of new transformers
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For ageing assessment of in-service transformers
Benefits
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Early detection of contamination
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Improved transformer reliability
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Reduced risk of dielectric failure
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Supports preventive maintenance strategy
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Enhances asset life