126kV dead tank CB PD eliminated via 3D simulation-optimized grading capacitor redesign. Voltage uniformity 93%, E-field <2.6kV/mm, zero PD in 24 months.

Project Overview

After the commissioning of a 126kV power project featuring triple-break vacuum dead tank circuit breakers, electric field simulation testing revealed a severe imbalance in voltage distribution across the breaks (74% at the high-voltage end, 19% in the middle, and 7% at the low-voltage end). The electric field intensity at the metal connectors reached 18kV/mm (exceeding the safety threshold by 5 times). After only 6 months of operation, abnormal partial discharge (PD) noises occurred at the high-voltage end interrupter, posing risks of insulation aging and interruption failure. Leveraging 3D electric field simulation technology, our company completed the reconstruction of the voltage grading system within 7 days: replacing the existing structure with a cylindrical grading capacitor design and precisely matching the capacitance parameters. Post-governance, the voltage distribution uniformity improved to 93%, electric field intensity dropped to 2.6kV/mm, and PD signals returned to zero. The equipment has operated stably for over 24 months, ensuring the safe operation of the project.

Exceptional Design · Root Cause Eradication

Focusing on the trinity of "Simulation-Driven - Structural Reconstruction - Precise Parameters":

• 3D Simulation Priority: Established a refined electric field model for the 126kV triple-break system to precisely locate floating potentials and electric field concentration points, providing quantitative calculations for the optimal grading solution.

• Structural Reconstruction & Upgrade: Replaced bilateral grading capacitors with an integrated cylindrical design, optimizing the layout of conductive rods and shields to reduce stray capacitance by 35%.

• Precise Parameter Matching: Customized grading capacitor values ensured that the voltage distribution uniformity across the breaks reached ≥ 90%, with electric field intensity strictly controlled within the safety threshold of ≤3 kV/mm.

Empowering Infrastructure Development

This case led to the development of the "Technical Guidelines for the Design and Verification of Voltage Grading Systems in High-Voltage Dead Tank Circuit Breakers," which has been promoted across 18 key 126kV/252kV projects nationwide, averting 29 electric field concentration hazards. Through a closed-loop technical system of "Simulation-Design-Verification," our company is driving circuit breaker grading design from an experience-oriented approach to precise quantification. This provides core support for enhancing the reliability of extra-high-voltage equipment and contributes to the construction of a safe and resilient new power system.