TRANSFORMERS, SUBSTATIONS + CABLES
Failsafe networking for high-level grid stability Jan Aulenberg, MSc, Product Manager in network technology, Phoenix Contact Electronics GmbH, Germany Photovoltaic systems have to play their part in ensuring high-level grid stability and supply reliability. Ethernet-based networking ensures the failsafe transmission of diagnostics data and control commands between the various installed inverters, transformer stations, grid connection points, and monitoring systems – via cable-based or wireless communication.
A s a renewable energy, photovoltaics (PV) are making a considerable, sustainable contribution to meeting the globally increasing demand for energy. Planning, constructing and managing large PV systems demands extensive expertise and experience. Zebotec GmbH, based in Konstanz, Germany, has established itself in this field over the past 15 years, to become one of the world’s leading independent system integrators for control systems in photovoltaic power stations. Zebotec is a part of the BayWa r.e. Group which, in 2009, brought together various companies from within the field of renewable energies. With its headquarters in Munich, the Baywa r.e. Group’s range of activities includes, among other things, the design, construction and marketing of PV power stations in the solar project management sector. In these projects, Zebotec’s responsibilities include the systems for monitoring and control technology and the construction of efficient Ethernet networks for networking system sections and for data exchange. VLANs prevent interference in communications The Ethernet networks installed in the photovoltaic systems are used to transmit the diagnostics data recorded in the inverters, the weather stations, the temperature sensors mounted in the transformer stations, and the energy measuring devices. Forwarding the control data for grid feed-in in particular, places high demands on the failsafe performance of this communication because, if the receiver does not receive the control values reliably, this may lead
to the system feeding into the power grid without control, which would in turn put grid stability at risk. Special considerations have to be taken into account when networking the individual transformer stations. A good example of this is in the 45 MW ground-mounted system in Oosterwolde de Boer, the Netherlands, realised by Zebotec and the Dutch subsidiary of BayWa r.e., GroenLeven. Firstly, there are large distances to be bridged between the stations in this system, and secondly, the Ethernet cables have been laid in cable ducts with very little clearance to the ac and dc cables in the system. Due to this proximity, electromagnetic interference (EMI) could arise if classic twisted-pair copper cables were used and, in the worst case, could result in loss of data. To prevent this, the copper cables would have to be equipped with special shielding or laid separately. Due to the length of the cables and the possibility of EMI influences, Zebotec decided to use fibreglass cables which, because of their immunity against electromagnetic interference, proved to be an installation-friendly and error-tolerant solution. Zebotec installed managed switches from Phoenix Contact at the central grid connection point to increase the stability of the network further. The Ethernet transmission of the transformer stations connected in several lines comes together here. In this topology, each line is configured as a separate virtual local area network (VLAN). This prevents the various system sections from being able to exchange data inadvertently – and further, prevents unnecessary data streams and improves communication efficiency.
Special considerations had to be taken into account when networking the individual transformer stations installed in the ground-mounted system.
The 2200 series Managed Switches incorporate various redundancy mechanisms and security functions.
22 Electricity + Control MARCH 2022
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