--- title: "Lightning arrester in industrial distribution" subject: "Industrial Power Distribution and Illumination" chapter: 2 key: "semester_6/industrial_power_distribution_and_illumination:lightning-arrester-industrial" source: https://www.bctengineer.com/q/semester_6/industrial_power_distribution_and_illumination/lightning-arrester-industrial site: BCT Engineering --- # Lightning arrester in industrial distribution Industrial Power Distribution and Illumination · Chapter 2: Earthing - Asked in: 2072 Asoj, 4 marks - Video: [Lightning Arrester | Substation Series | In Hindi](https://www.youtube.com/watch?v=D5TGaUMwtMY) — TechInsight - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/industrial_power_distribution_and_illumination/lightning-arrester-industrial - Whole chapter: https://www.bctengineer.com/md/semester_6/industrial_power_distribution_and_illumination/chapter-2 ## Question Explain about lightning arrester used in industrial power distribution. ## Short answer A lightning arrester connects line to earth, acting as an insulator at normal voltage but conducting surge currents to ground, limiting residual voltage below equipment insulation level. Metal-oxide gapless types are most common in industry, installed at incoming HV lines, transformer bushings, cable terminations, and LV panels with SPDs. Short straight earth leads and low-resistance earthing are essential. ## Answer 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 ```text 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. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How does a lightning arrester behave at normal voltage and during a surge? A. Conducts always and blocks surges B. Insulates at normal voltage and conducts the surge to earth above a set voltage C. Insulates both times D. Opens the line permanently on a surge Answer: B. The non-linear element has high resistance at normal voltage and falls sharply during a surge, limiting the voltage. (Key point: Arrester behaviour) 2. What must the arrester's residual voltage be relative to the equipment's insulation level (BIL)? A. Above the BIL B. Equal to the BIL exactly C. Below the BIL D. Unrelated to BIL Answer: C. The residual voltage held at the equipment must be below its insulation level so the equipment is not damaged. (Key point: Residual voltage) 3. Which type of arrester is most common today? A. Rod gap B. Silicon carbide valve type C. Horn gap D. Metal oxide (ZnO) gapless Answer: D. ZnO gapless arresters are fast, have no series gaps and good energy capacity. (Key point: Most common type) 4. Where should an arrester be installed and earthed? A. Far from the transformer with a long earth lead B. Close to transformer bushings with a short, straight lead to a low-resistance earth bonded to station earth C. Only at the load end with no earthing D. Inside the transformer oil with no earth lead Answer: B. Close mounting and a short, straight lead to a bonded low-resistance earth minimise the voltage the equipment sees. 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