What Is an Arcing Horn and How Does It Protect High-Voltage Equipment?

INTRODUCTION

An arcing horn is a protective device installed on high-voltage equipment to prevent damage during overvoltage events. It consists of two conductors: one connected to the energized line and the other to ground. The two conductors are separated by an air gap that intentionally becomes the preferred path for a flashover when voltage exceeds a critical level. Arcing horns are commonly installed on bushings, outdoor insulators, and high-voltage transmission structures to prevent flashover across insulation surfaces, which can lead to permanent damage.

Arcing horn [1] 

HOW ARCING AIR GAP WORKS

Under normal operating conditions, the air gap between the conductors is an insulator. When an overvoltage occurs—such as a lightning strike, switching surge, or abnormal system transient—the electric field across the gap increases. Once the electric field exceeds the dielectric strength of air, the gap becomes ionized and a controlled flashover forms.

This redirected flashover protects the insulator by providing a lower-resistance path to ground. Therefore, the air-gap spacing is the most critical design parameter. It must be chosen to:

• withstand normal operating voltage

• flash over at a predictable overvoltage level

• avoid accidental or premature discharge

Proper sizing ensures consistent performance across various environmental and fault conditions.

SIMULATING ARCING HORN BEHAVIOR

Physical testing of arcing horns can be expensive and time-consuming, especially when evaluating different air-gap distances or conductor geometries. Virtual prototyping provides a practical alternative.

Using EMWorks EMAG, designers can simulate:

• electric field distribution

• voltage gradients

• displacement fields

• breakdown locations

• safety factor across the insulator surface

Because EMAG operates directly inside the CAD environment, the full workflow—including geometry definition, material assignment, meshing, and post-processing—occurs without external data transfer. This helps engineers evaluate multiple design variations efficiently.

Vector plot of the electric field at 50kV  

Electric field lines at 250kV  

Animation of the electric field versus applied voltage

Voltage plot 

Animation of Safety Factor results – detection of breakdown voltage  

These outputs allow engineers to identify overstressed regions, optimize the air-gap distance, and confirm that the flashover will occur on the horn—not across the insulator.

SUMMARY

Arcing horns provide essential protection for high-voltage equipment by directing flashover away from bushing and insulator surfaces during overvoltage events. Their performance depends strongly on the air-gap distance and conductor geometry. Using EMWorks EMAG for virtual prototyping enables engineers to evaluate electric-field behavior, tune the air gap, and predict breakdown conditions before building hardware, reducing development cost and improving reliability.

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