A surge arrester is a crucial electrical protection device designed to limit voltage spikes on electrical equipment, preventing damage caused by lightning strikes or power surges. It quickly discharges or bypasses surge currents to protect equipment and ensure the continuity and reliability of the power system. Surge arresters are designed in accordance with ANSI standard C62.11, allowing them to repeatedly perform these protective functions. Importantly, surge arresters do not absorb or stop lightning but instead direct lightning currents, limiting voltage fluctuations to protect parallel-connected devices.
Why Use a Surge Arrester?
The distribution power line encounters various voltage surges, with lightning being the primary source. Approximately 100 lightning strikes occur on the Earth’s surface every second, and lightning is a random and unpredictable event. Additionally, other sources of voltage surges include switching surges and temporary overvoltages.
● Switching Surges: These are overvoltages produced by changes in operating conditions within the system and are the main voltage surge for station-class arresters. Switching surges involve the trapping of energy and its subsequent release, which can potentially damage equipment.
● Temporary Overvoltages: These typically result from ground faults on one phase, causing voltage rises on the unfaulted phases until the fault can be cleared, thereby increasing the risk of equipment damage.
Hence, using a surge arrester is an effective means of protecting electrical equipment from these potential threats.
How Surge Arresters Work
Surge arresters provide protection through their internal nonlinear resistive materials:
1. Voltage Monitoring: Surge arresters continuously monitor the voltage levels in the power system.
2. Rapid Response and Conduction: When the voltage exceeds a safe threshold, the surge arrester quickly becomes conductive, providing a low-resistance path to divert excess current to the ground.
3. Recovery and Insulation: After the overvoltage event subsides, the surge arrester returns to a high-resistance state, continuing to insulate and preparing for the next voltage change.
Classification and Functions of Surge Arresters
Surge arresters can be categorized into various types based on functions and materials, each with unique applications:
1. Metal Oxide Surge Arresters (MOA): Featuring a gapless design, these are quick to respond and provide excellent protection performance, widely used in modern distribution and transmission systems.
2. Silicon Carbide Surge Arresters: While traditionally used, these are gradually being replaced by newer technologies but still serve in some applications.
3. Elbow Surge Arresters: Specifically designed for cable joints, providing compact protection in underground and complex environments.
4. Combined Surge Arresters: Integrating breaker or fuse functions to provide comprehensive overvoltage protection for equipment.
Application of Surge Arresters in Transformers
Transformers are the heart of the power system, and their protection is paramount. The application of surge arresters in transformers primarily includes:
1. Protection at Incoming and Outgoing Lines: Surge arresters are typically installed at the incoming and outgoing lines of transformers to prevent direct impacts from lightning and surges.
2. Suppression of Transient Overvoltages: Surge arresters can quickly limit transient voltage spikes, protecting transformer windings.
3. Enhancement of System Reliability: Utilizing surge arresters can reduce the frequency of equipment damage, saving on maintenance and replacement costs.
Surge arresters are extensively used in power systems, from protecting residential homes to utility substations. They are installed at various locations, including residential circuit protection, indoor transformers, overhead transformer locations, and within substations. Standards are defined by IEEE standard C62.11 and IEC standard 60099-4, ensuring consistent performance and effectiveness of surge arresters globally.
