The European Commission has introduced new guidelines increasing the maximum voltage for power generation systems. Following these updates, many Polish distribution companies have set their own regulations, making it challenging for designers to select appropriate arrester parameters. Here, we explain how to interpret the new guidelines accurately and meet specific requirements, including the significance of the 145 kV value in these designs.

Changes in Maximum System Voltage

The latest European Commission guidelines state that the maximum system voltage U_s can no longer be 123 kV but must be 126.5 kV (for one hour). This adjustment is outlined in Commission Regulation (EU) 2016/631, establishing a network code on the requirements for connecting generating units to the power grid (NC RfG).

Voltage Conditions from NC RfG Article 25(1):

• Voltage range: 1.118 pu – 1.15 pu – Operating time: 60 minutes;
• Voltage range: 1.05 pu – 1.10 pu – Operating time: 60 minutes.

This regulation reflects the characteristics of green energy generation in facilities such as hydropower plants, wind farms, photovoltaic farms, and other generating units. As a result, surge arresters must be selected accordingly.

Issues Arising from the New Guidelines

Designers faced confusion about which surge arrester parameters to adjust to comply with the new regulations, especially for 110 kV systems (nominal voltage, U_N). Previously, in Poland, the maximum voltage (U_M, now U_s) was 123 kV, and equipment, including surge arresters, was chosen to match this value for optimal operation, protection, and longevity.

Surge Arresters for Western European Projects

Most RES projects in Poland originate from Western Europe, where 110 kV systems are used but with different configurations. For example, Germany uses a U_n of 132 kV and a U_s of 145 kV, complicating the selection of arresters for Polish implementations.

Selecting Arresters for U_s = 126.5 k

To select an arrester for a system with a maximum voltage of 126.5 kV (for one hour), calculate as follows: 126.5 kV / √3 = 73.12 kV. Standard arresters with a U_c of not less than 77 kV are sufficient. Thus, no special selection is required for this condition.

Addressing the 145 kV Requirement

Standard arresters for 110 kV systems can safely handle a U_s of 126.5 kV for one hour. However, the 145 kV parameter seen in Western European projects does not apply to Polish networks but can be addressed by using an arrester with U_r = 96 kV / U_c = 77 kV in a higher sheath to meet the insulation strength condition for a network with U_s 145 kV. Many Proxar® surge arresters can be manufactured with this longer sheath at an acceptable cost.

Proxar®: Your Trusted Partner in Surge Arrester Selection

At Proxar®, we offer not only high-quality surge arresters but also expert advice and support in selecting the right arresters for your needs, ensuring compliance with both European and Polish standards. Unlimited trust in our products and services is our commitment to you.

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