Lightning arrester in industrial distribution

A lightning arrester (surge arrester) is a protective device connected between line and earth. It sends high-voltage surges (from lightning or switching) to earth and so protects transformers, switchgear and cables in an industrial distribution system. At normal voltage it behaves as an insulator; above a set voltage it conducts and limits the voltage.

Working

 Line ──┬────────── to transformer
        │
      [LA]  non-linear resistor (ZnO)
        │
      [E]  earth (short, straight lead)

• At normal voltage the arrester draws only a tiny leakage current.
• When a surge arrives, its resistance falls sharply and it conducts the surge current to earth, holding the voltage at the equipment to its residual voltage, which is below the insulation level (BIL) of the equipment.
• After the surge passes, it returns to the insulating state and the normal power-frequency current does not continue to flow.

Types used

• Metal oxide (ZnO) gapless arrester: most common today; fast, no series gaps, good energy capacity.
• Valve type (SiC with series gaps): older type.
• Rod gap / horn gap: simple, cheap backup protection on lines.
• Low-voltage surge protective devices (SPDs) in LV panels to protect electronics and drives.

Use in industrial power distribution

• At the incoming HV line and on both sides of the distribution transformer (mounted close to the bushings).
• At cable terminations where overhead lines change to underground cable.
• SPDs in main LV panels and in control/PLC panels.

Requirements

• Rated voltage and discharge current (typically 5 kA or 10 kA) suited to the system.
• Short, straight earth lead to a separate low-resistance earth pit, bonded to the equipment body and station earth.
• Periodic testing of insulation and leakage current.