Surge arresters are indispensable for medium and high voltage power networks. These devices are utilized across various power and industrial sectors, including renewable energy sources (RES). However, selecting the right surge arresters for each project is crucial. Discover why this selection process is so vital.

Understanding Surge Arresters and Their Function

Surge arresters are electrical devices with non-linear properties designed to protect power systems from overvoltages, such as those caused by lightning strikes or power system switching. When properly selected and operating within their rated conditions, they do not disrupt the power grid. Their primary function activates during overvoltage events, diverting the excess voltage to the ground and reducing it to safe levels, ensuring smooth operation of the equipment and power systems they protect. Surge arresters are engineered for long-term reliability, capable of handling multiple short-duration overvoltage events over decades of service.

Operating Under Harsh Conditions

Surge arresters must perform reliably under harsh environmental conditions, including:

• Prolonged exposure to sunlight and UV radiation.
• Extreme temperature fluctuations.
• Various forms of precipitation.
• Mechanical stresses.

Despite these challenges, well-selected surge arresters provide broad protection. For instance, they can effectively dissipate surges up to 100 kV in a 15 kV nominal voltage network. Such high-potential surges can occur repeatedly, and surge arresters are expected to maintain their performance for up to 30 years.

Key Parameters for Selecting Surge Arresters

• Selecting the right surge arrester involves considering multiple factors:
• System’s highest voltage (U_s).
• Short-circuit current at the installation point.
• Ground fault coefficient.
• Maximum duration of ground faults.
• Power grid grounding and protected equipment connections.
• Cable section lengths.
• Distance between arresters and protected equipment.
• Continuous operating voltage (U_c) relative to the network’s U_s.
• Arrester’s rated voltage for TOV surges.
• Expected lightning discharge currents.
• Equipment’s rated insulation level.

After determining these parameters, the next steps include assessing the arrester’s protective characteristics against lightning and switching surges and selecting the optimal installation location, ideally as close to the protected equipment as possible. However, technical constraints of the project or facility can sometimes make this challenging, as experienced with one of our clients in Poland.

Consequences of Improper Arrester Selection

Choosing the correct surge arrester parameters is a collaborative effort among designers, operation supervision services, and companies like Protektel, which provide expert support. Relying solely on schematic diagrams or network design descriptions can lead to significant responsibility, as improper selection can have dire consequences. For example, failure of a 400 kV transmission network due to an incorrectly chosen arrester could disrupt power to critical infrastructure, including hospitals and industrial facilities. An example of the severe repercussions of improper selection is the Jaworzno power plant in Poland, which supplies 10% of the country’s electricity. A failure here could lead to widespread and difficult-to-repair outages, with catastrophic national consequences.

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