Why is the increase in micro-ohm (μΩ) resistance unacceptable in sealed GIS pipes?

Q: GIS internal circuits carry thousands of Amperes. Why must we address a resistance rise from 30μΩ to 100μΩ, even if it seems small?

A: Because at high current, tiny impedances result in massive heat.

• Calculation Example: Assume a running current of 4000A.

• At 30μΩ, Power P = I²R = 4000² × 30 × 10⁻⁶ = 480W (equivalent to 5 lightbulbs).

• At 100μΩ, Power P = 1600W (equivalent to a high-power space heater).

• Consequences: GIS is completely sealed, making heat dissipation difficult. 1.6kW of heat can cause local temperatures to soar, leading to SF6 gas decomposition and acid formation. These acids etch insulators, eventually causing ground faults or explosions.

Conclusion: Doubling the resistance doubles the risk. 100A+ high-current testing is mandatory to ensure resistance is within acceptable limits.

Why must GIS switch operations be "Lightning Fast"?

Q: Why must circuit breaker opening times be accurate to milliseconds (ms)?

A: It is critical for Arc Quenching success.

1. Arc Quenching Window: Current zero-crossing occurs every 10ms at 50Hz.

2. High-speed Stretching: Slow opening lets the arc linger, overwhelming the SF6 cooling capacity and potentially melting contacts.

Criteria: 110kV+ breakers typically require 20-40ms opening times.