Electricity and Control October 2022

COVER ARTICLE

Protection of DC systems in photovoltaic installations

T he use of renewable energy sources has become increasingly important in recent years. In addition to wind turbine generators, hydroelectric plants or biomass systems, photovoltaic power generation systems (PV systems) supply a significant portion of renewable energy. PV systems are designed, for example, as rooftop systems on private homes and industrial buildings as well as free standing systems. Due to their exposed location, the systems are vulnerable to increased risk of damage by the effects of lightning. To prevent such damage and the associated loss of system availability, lightning and surge protection measures need to be considered during the design phase. Standards and directives tailored specifically to PV power supply systems make it easy to plan lightning and surge protection for these systems. Free-standing PV systems with external lightning protection Compared to lightning protection in physical structures, other aspects become relevant for the design of effective lightning and surge protection systems for free-standing PV installations. These include: ƒ Use of inverter types (string or central power inverters). Free-standing systems are generally characterised by a high intermeshed equipotential bonding system, which is normally equipped with numerous ground connections. The module frames are also connected to the equipotential bonding system. The cable lengths between the PV ƒ Equipotential bonding mesh width ƒ Design of the grounding system

panels and the feeding point can be several hundred metres in these systems. If lightning strikes the external lightning protection system, partial lightning currents are coupled into the equipotential bonding system. Therefore, free standing systems with central power inverters on the dc side need to be protected using type 1 SPDs (surge protection devices). The required performance for these is specified in the table below. For free-standing systems with string inverters installed near the PV panels, the following guide applies. To protect the AC side, choose SPDs with a discharge capacity analogous to the values shown in the table below. To protect the DC side, it is sufficient to use type 2 SPDs with a discharge capacity of at least 5 kA (8/20 μs) per mode of protection. VALVETRAB-MB-...-DC-PV The costs of a PV system can be significantly reduced by a high DC system voltage of up to 1 500 V. Fewer string combiner boxes are needed, and material costs for cable installation are also reduced. With the VAL-MB product range, Phoenix Contact is setting new standards with high performance SPDs for voltages up to 1 500 V DC. The range features a high total discharge capacity of 12.5 kA (10/350 μs) and thus satisfies all standard requirements and conditions of the installation guideline for use in lightning protection classes III and IV. □

The VALVETRAB VAL-MB-T1/ T2 1500DC-PV/2+V-FM.

Lightning current parameters ( I 10/350 ) and I n ( I 8/20 ) for SPDs on the DC side in free-standing PV systems with a central power inverter.

For more information contact Cameron Taylor at Phoenix Contact South Africa. Tel: +27 (0)11 801 8200, email: ctaylor@phoenixcontact.co.za, visit: www.phoenixcontact.co.za

OCTOBER 2022 Electricity + Control

3