Surge Arresters; Surge arrester works principle; Surge Suppersors

Surge Arresters: Types, Working, and Applications

Surge arresters are one of the most important protective devices in electrical systems. They work on the same principle as lightning arresters—providing a low-impedance path to earth for transient overvoltages or lightning strikes, and then quickly restoring the circuit back to normal operating conditions.

👉 Think of a surge arrester like a safety relief valve in a boiler or hot water heater. When pressure (voltage) exceeds safe limits, the valve (arrester) opens and safely releases it to ground. Once the voltage returns to normal, the arrester resets and is ready for the next surge.

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Functions of a Surge Arrester

1. Provide a discharge path – Allow transient overvoltage (spike/surge) to pass to ground.
2. Prevent follow current – Stop continuous current from flowing to ground after the surge has passed.

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Types of Surge Arresters

1. Expulsion Type Arrester

• Uses a series spark gap in a fiber tube.
• When a surge occurs, an arc forms and gases are expelled, quenching the arc.
• Low cost but requires frequent maintenance.

2. Valve Type Arrester

• Uses nonlinear resistors (silicon carbide) in series with spark gaps.
• Provides better voltage control compared to expulsion type.

3. Gapless Metal-Oxide Arrester (MOA)

• Uses zinc oxide blocks without series spark gaps.
• Provides very fast response and superior protection.
• Most widely used modern surge arrester.

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Surge Protective Devices (SPDs) by IEC Standard

Type	Installation Point	Tested Withstand	Use Case
Type 1	Main distribution board (with LPS)	Class I, 10/350 µs impulse	Direct lightning strike protection
Type 2	Main switchboard or sub-panels	Class II, 8/20 µs current	General surge protection in buildings
Type 3	Near sensitive equipment	Combination waveform (1.2/50 µs – 8/20 µs)	Protect delicate electronics

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Surge Arresters by Class

Class	Application	Equipment Range
Substation Class	High voltage substations, >20 MVA equipment	Heavy-duty protection
Intermediate Class	Transformers, substations, 1–20 MVA	Medium-voltage protection
Distribution Class	Distribution transformers, 100 kVA range	Commonly used in networks
Secondary Class	Small appliances, low-level protection	Minimal protection, not for sensitive electronics

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Other Protective Devices

1. Earthing Screen – Provides shielding to substations/power stations by diverting lightning directly to ground.
2. Overhead Ground Wires – Installed above transmission lines to intercept lightning strikes.
• ✅ Effective, simple to implement
• ❌ Expensive, risk of short circuits if they fall on conductors
3. Lightning Arresters – Work along with surge arresters to safeguard overhead lines and substations.

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Key Takeaway

• Lightning arresters → Protect against direct strikes.
• Surge arresters → Protect against transient overvoltages (switching + lightning-induced surges).
• Modern installations rely heavily on gapless metal-oxide arresters (MOAs) for reliability.

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