Evaluates Oil-Impregnated Paper (OIP) and Resin-Impregnated Paper (RIP) condenser bushing health by normalizing measured tan delta to 20°C and verifying that main capacitance C₁ deviation remains within the ±5% IEEE threshold.
Governing Formulas & Standards
Standards Basis: IEEE Std C57.19.100 / IEC 60137
\tan\delta_{20} = \frac{\tan\delta_m}{k_\theta} \quad ; \quad \Delta C_1\% = \frac{C_{meas} - C_{nameplate}}{C_{nameplate}} \times 100\%
Applies temperature correction factor k_theta to measured dissipation factor and calculates percentage change in capacitance.
Worked Engineering Example: 132 kV OIP Condenser Bushing Doble Test Evaluation
- Tan Delta Temperature Correction to 20°C: k_θ = 1.15 at 30°C -> tan δ_20 = 0.42% / 1.15 = 0.365% → 0.365% (PASS: < 0.50%)
- Capacitance Deviation Check: ΔC1 = (325 - 320) / 320 × 100% = +1.56% → +1.56% (PASS: < 5.0%)
Final Solution: Tan Delta (20°C): 0.37% (Good) | C1 Deviation: +1.56% (Normal Foil Integrity)
Frequently Asked Questions
- Why is a rise in bushing capacitance C1 considered dangerous?
- Condenser bushings contain concentric capacitive aluminum grading foils separated by oil-paper insulation. When an insulation layer punctures, those foils short together, which increases the total capacitance C1. If multiple foils fail, the remaining insulation suffers severe overstress, leading to catastrophic explosive bushing failure.
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