What is a surge arrester, and how does it protect power systems?

Short Answer:

A surge arrester is a protective device used in electrical power systems to protect equipment from sudden high voltage surges, such as those caused by lightning or switching operations. It is connected between the line and ground and allows the extra voltage to safely pass to the ground without damaging the system.

Surge arresters protect transformers, circuit breakers, and other equipment by stopping the high-voltage surge before it enters the system. They act very fast and only work during abnormal conditions, ensuring smooth and safe operation of the entire power network.

Detailed Explanation:

Surge arrester and how it protects power systems

Power systems are exposed to sudden voltage surges due to natural and man-made reasons. Lightning strikes, switching operations, or faults can cause high voltages that are far above the normal level. If these surges enter the system, they can damage insulation, burn wires, destroy equipment, and cause outages.

To avoid this, surge arresters are used. A surge arrester is a safety device that is installed between the live conductor and the ground. Its job is to protect the electrical system from overvoltage conditions by safely directing the high surge voltage to the earth. It works very fast and becomes active only when a surge occurs.

How a Surge Arrester Works

  1. Normal Condition
    Under normal voltage, the surge arrester remains non-conductive. It acts like an open circuit and does not affect the system.
  2. During Surge Condition
    When a high-voltage surge occurs (due to lightning or switching), the voltage suddenly rises above a safe level.
  3. Surge Absorption
    The surge arrester detects this rise and instantly becomes conductive. It creates a low-resistance path for the extra voltage to flow directly to the ground.
  4. Return to Normal
    Once the surge passes and the voltage returns to normal, the arrester again becomes non-conductive and stops the current flow to ground.

This quick response helps protect sensitive equipment and avoids system failure.

Types of Surges in Power Systems

  1. Lightning Surges
    Caused by direct or nearby lightning strikes. These are very fast and dangerous. A surge arrester redirects this energy safely to the earth.
  2. Switching Surges
    Caused by sudden changes in load or switching of high-voltage lines. Though not as powerful as lightning, they still need to be controlled.
  3. Temporary Overvoltages
    These are not as fast but can last longer and damage the insulation of equipment if not protected.

Surge arresters are designed to handle all these types effectively.

Types of Surge Arresters

  1. Metal Oxide Varistor (MOV) Type
    Most commonly used today. Uses zinc oxide blocks that change their resistance based on voltage. Highly efficient and requires no spark gap.
  2. Expulsion Type
    Used in medium-voltage systems. Uses an arc inside a tube to break the surge.
  3. Valve Type
    Older design using silicon carbide. Now replaced by MOV-based designs due to better performance.

Applications in Power Systems

  • Transmission Lines: Installed at entry and exit points of substations.
  • Distribution Lines: Mounted on poles to protect transformers and meters.
  • Substations: Protect expensive equipment like transformers, breakers, and busbars.
  • Industrial and Residential Areas: Protect sensitive electronic equipment from voltage spikes.

Importance of Surge Arresters

  • Protect Equipment: Prevent insulation breakdown, transformer burnouts, and panel damage.
  • Avoid Power Failures: Keeps the system running during surges.
  • Improve System Reliability: Reduces maintenance and increases the lifespan of equipment.
  • Fast Response: Works in milliseconds to stop dangerous surges.
  • Cost Saving: Avoids costly damage and repair.

Difference from Lightning Rod

It is important to note that a surge arrester is not the same as a lightning rod.

  • A lightning rod protects buildings by diverting lightning to the ground.
  • A surge arrester protects electrical systems from overvoltages by working inside the circuit.
Conclusion

A surge arrester is a vital device used in power systems to protect against high-voltage surges. It works by providing a safe path for the extra voltage to flow to the ground, protecting equipment and improving the reliability of the power supply. It stays inactive during normal operation and acts only when a surge occurs. Because of its fast response and ability to handle large voltages, it is an essential part of any modern power distribution and transmission system.