Dispersive Characteristics Of Expulsion Lightning Arresters In Medium Voltage Grids

The dispersion of an expulsion lightning arrester refers to the significant variation in its sparkover voltage and discharge time under identical surge conditions. This high statistical scatter occurs because gas production relies heavily on the internal arc eroding the tube wall, making the protection level unpredictable and severely compromising grid insulation coordination.

Factors leading to high dispersion in breakdown voltage

Internal Arc and Environmental Influence

1. Ambient humidity and atmospheric pressure directly alter the air gap breakdown voltage inside the tube.

2. Repeated operations cause progressive inner wall erosion, changing the critical dimensions required for gas generation.

3. Intermittent gas discharge dynamics create unpredictable pressure variations, which fluctuates the exact moment of arc interruption during a lightning strike.

Consequences for Grid Insulation Coordination

Vulnerabilities in Distribution Networks

High dispersion disrupts the voltage coordination between protection devices and transformers. For instance, a standard 10 kv lightning arrester might fail to spark over before the transformer insulation degrades. Similarly, an installed 11 kv lightning arrester or an older 11 kv lighting arrester might exhibit delayed response times, exposing downstream substation equipment to catastrophic residual voltage spikes exceeding 75 kV.

Mitigating Dispersion Risks in Substation Engineering

Selecting appropriate overvoltage protection devices requires analyzing how operational profiles change over heavy discharge cycles. Field engineers manage critical insulation margins by comparing the degradation rates of legacy gas-evolving designs against modern solid-state alternatives. The data below details the specific performance deviations that dictate long-term grid reliability and asset protection.