Substations, transformers, and essential equipment face constant risks from lightning strikes or switching surges, posing threats of damage and downtime. Surge arresters are indispensable in maintaining the resilience and longevity of high-voltage electrical systems.
In this blog, we will explore their construction, operating principles, and the selection criteria crucial for ensuring effective protection against transient overvoltages.
Understanding Surge Arresters
Surge arresters are crucial devices designed to protect electrical equipment from the harmful effects of transient overvoltages. These voltage spikes can result from lightning strikes, grid-switching operations, or faults in the system. The primary function of a surge arrester is to offer a low-impedance path to the ground during such events, redirecting excess voltage away from the protected equipment.
Types of Overvoltages
There are two main types of overvoltages that surge arresters protect against:
Lightning-Induced Overvoltages
Lightning strikes near power lines or equipment can cause extremely high voltages. Surge arresters are crucial for intercepting this energy and preventing it from reaching and damaging sensitive components.
Switching Surges
Rapid changes in current flow when electrical equipment such as circuit breakers or transformers switch on or off can generate surges. Surge arresters help mitigate these surges, ensuring smooth and uninterrupted operation of the power system.
Evolution of Surge Arrester Technology
Over the years, surge arresters have undergone significant development. Initially, surge arresters were designed with a gap and a nonlinear resistor enclosed in porcelain. Although effective, these gapped surge arresters had limitations such as higher residual voltages and shorter lifespans. However, advancements in materials and design led to the rise of gapless surge arresters, particularly those employing Zinc Oxide (ZnO) technology.
Zinc Oxide Surge Arresters
Zinc Oxide surge arresters are the modern standard in surge protection. They are made up of a stack of ZnO discs enclosed in a sealed porcelain or polymer housing. Unlike gapped arresters, ZnO surge arresters offer superior performance characteristics:
- Nonlinear Behaviour: Under normal operating conditions, ZnO discs exhibit high impedance, effectively isolating the protected equipment.
- Low Impedance During Surges: During overvoltages, the ZnO discs become conductive, providing a path to ground and limiting the voltage across the protected equipment.
Applications of Surge Arresters
Surge arresters find application across a wide range of sectors, from utility-scale power systems to industrial facilities.
Utility Substations
Surge arresters are installed near transformers and circuit breakers in substations to protect against lightning and switching surges.
Industrial Environments
They are crucial for safeguarding sensitive equipment such as motors, drives, and control systems from power disturbances.
Specialised Applications
Surge arresters are deployed in Gas Insulated System (GIS) substations and Ultra-High Voltage (UHV) transmission lines to maintain the reliability and integrity of the power system.
Testing and Maintenance of Surge Arresters
Ensuring the efficacy of surge arresters requires regular testing and maintenance protocols.
Testing Procedures
Conduct routine tests to verify the surge arrester’s response to simulated overvoltages.
Commissioning
Follow guidelines for the proper installation and commissioning of new surge arresters to ensure they meet performance specifications
Maintenance Practices
Implement periodic inspections to detect physical damage, monitor leakage currents, and assess any signs of deterioration over time.
Advances in Surge Arrester Technology
Recent advancements in surge arrester technology focus on enhancing performance and reliability.
Metal Oxide Varistors (MOVs)
These next-generation surge arresters utilising MOVs offer improved surge handling capabilities and faster response times compared to traditional gapped designs.
Digital Integration
Integration with smart grid technologies facilitates enhanced monitoring, diagnostics, and rapid response to power disturbances.
Surge Arresters in High-Voltage Substations
Surge arresters are crucial components in high-voltage substations, designed to protect equipment such as transformers, circuit breakers, and bushings from lightning strikes and switching surges. Installed in parallel with the equipment they safeguard, these devices redirect surge energy safely to the ground, preventing voltage spikes that could otherwise damage insulation.
Insulation Coordination and Its Role
Insulation coordination involves selecting equipment dielectric strength in relation to potential system overvoltages. Surge arresters are integral to this process in electrical power systems. Without these, equipment would be vulnerable to high dielectric stresses from lightning and switching overvoltages. Surge arresters maintain voltage below the equipment’s withstand level with a safety margin, essential for system reliability.
Construction and Components
Modern surge arresters predominantly use gapless metal-oxide (MO) varistors. These varistors, made of zinc oxide and other metallic powders compressed into discs, form the active part of the surge arrester unit. The diameter of these discs determines energy-handling capacity, crucial for high-voltage applications. Within the surge arrester housing, these varistors are stacked with spacers to maintain uniform pressure and secure electrical contact.
Condition Monitoring and Longevity
Monitoring the health of surge arresters is critical due to their role in protecting costly equipment. Devices such as surge counters and leakage current monitors track operational parameters, detecting potential faults or degradation. With proper configuration, modern MO surge arresters can operate almost maintenance-free for over 30 years, ensuring long-term system stability.
Operating Characteristics and Selection
Surge arresters exhibit nonlinear voltage-current characteristics suited for surge protection. Key parameters such as Maximum System Voltage (Us), Continuous Operating Voltage (Uc), Rated Voltage (Ur), and protective levels (SIPL, LIPL) define their performance under various conditions. Selection involves balancing protective margins with operational stability, essential for reliable operation in high-voltage environments.
Surge Arresters & Transformers
The role of a surge arrester in transformers is crucial for protecting them from transient overvoltages, which can occur due to lightning strikes, switching operations, or other disturbances in the electrical grid. Here’s how surge arresters contribute to the protection of transformers:
Voltage Spike Diversion
Surge arresters are installed in parallel with transformers. Their primary function is to divert excessive voltage spikes away from the transformer winding and insulation. This helps prevent the transformer from being subjected to voltages beyond its design limits, which could otherwise lead to insulation breakdown and subsequent damage.
Limiting Overvoltages
During a voltage surge, the surge arrester quickly conducts excess current to ground, thus limiting the voltage across the transformer terminals. This protective action ensures that the transformer is not exposed to dangerously high voltages that could compromise its insulation and operational integrity.
Enhancing Transformer Lifespan
By preventing insulation damage and protecting internal components from overvoltages, surge arresters contribute significantly to extending the operational lifespan of transformers. This is critical as transformers are expensive assets in power systems and any downtime caused by damage can be costly.mer terminals. This protective action ensures that the transformer is not exposed to dangerously high voltages that could compromise its insulation and operational integrity.
Maintaining System Reliability
Transformers play a vital role in electrical distribution and transmission networks. The reliable operation of these transformers is essential for maintaining a continuous power supply. Surge arresters help in safeguarding transformers against unexpected voltage surges, thereby enhancing overall system reliability.
Final Thoughts
In conclusion, surge arresters play an indispensable role in safeguarding electrical infrastructure from transient overvoltages. From their inception with gapped designs to the adoption of advanced Zinc Oxide technologies, surge arresters have evolved to meet the increasingly stringent demands of modern power systems. As technology continues to progress, future innovations promise even greater protection capabilities, ensuring the reliability, resilience, and efficiency of electrical networks worldwide.
Understanding the importance of surge arresters and embracing technological advancements enables utilities and industries to fortify their power systems against unforeseen disruptions. By investing in surge protection solutions such as UPT (Universal Power Transformer), organisations can mitigate risks, enhance operational efficiency, and ultimately reduce maintenance costs associated with equipment downtime and repairs.
