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TestMeasuredTypical/ExpectInterpretation
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IR (5 kV, 20 °C)350 MΩ≥100–200 MΩAcceptable but not robust
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PI1.6≥2.0 desirableMoisture suspicion
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Tan-δ (HV-E) @10 kV0.8%≤0.5–0.7% (age dependent)Elevated losses
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Oil BDV42 kV/2.5 mm≥50–60 kV (new)Degraded oil
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Moisture (oil)25 ppm<10–15 ppm (good)Wet insulation trend
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DGA – H₂ 180 ppm; C₂H₄ 120 ppm; C₂H₂ 5 ppm
RisingThermal fault <700 °C; negligible arcingHot spot likely (OLTC? winding?)
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