Test & measurement
What is the RTU responsible for on-site?
At small sites, the RTU is both the site controller and the site communications gateway. The RTU collects data directly, and can also provide a secure VPN, to other devices that may be operating on site, such as, programmable logic controllers (PLCs) managing solar panel tilt and azimuth control, weather stations and digitally networked power relays. The collected data is then made available to the grid operators who can issue commands back to the RTU to regulate the station. In parallel, the RTU relays key information to the asset owner or investor and to maintenance crews. In Australia, data is also sent in parallel to
cloud based data servers for local communities and schools, for educational purposes. With its ability to report alarms and historical data via email, SMS, FTP and MQTT, a TBox is the ideal choice for small power plants that need to manage both physical assets and wider communications demands.
Can RTUs be used with “non-grid” power networks?
Yes, large facilities such as hospitals, universities, airports and railway lines often have their own internal power network that needs management. They have the same control and
communications requirements as the main grid, at marginally less complexity. Electrified railway networks, too, source their
main supply from the grid and then distribute the power along the railway network. The demands on RTUs used in the Railway Network have many similarities to a Power Network RTU - they are exposed to remote environments, occasional voltage spikes and must be able to store, manage and report large volumes of data and above all else, control the local switchgear.
Are smaller RTUs resilient to the network environment?
Yes, an important feature with any RTU is resilience to the site environment. Ovarro RTUs can operate in these rugged conditions at temperatures between -40 and +85 degrees Celsius and have up to 5,000 volts of isolation on I/O cards to protect the CPU from spurious electrical events. In addition to being resilient to the
environment, RTU systems should have layers of redundancy so it can continue to operate even if a major event damages one piece of the system. The Kingfisher RTU for example, can be configured with fully redundant Power Supplies, CPUs, and multiple communication paths. It means they can continue to manage intensive SCADA and telemetry applications, even in the event of a par tial system failure.
INS-APR20-LABFACILITY.qxp_Layout 1 17/04/2020 15:23 Page 1 What if the power generator fails?
RTUs have always operated in areas where power is either unreliable or unavailable. Each Ovarro RTU draws only a few Watts and can easily run off a solar power system or even a small and insignificant feed from the site generator. The RTUs also incorporate a battery management system and can run off a small rechargeable battery for extended periods. This removes the need for a UPS for the RTU. In addition, Kingfisher RTUs support multiple power supplies so that parallel connections to AC and DC supply systems can be used.
How will RTUs evolve in the future?
For many years there has been an ongoing trend in increasing the volume of data collected from the field. This centralised data collection and analysis are vital for long term trend identification and planning, however, a localised response is still required for low latency control. If you need a field hardened PC, or “edge computer” for monitoring electrical current, temperature, emissions, power and asset health, then you need an RTU. RTUs are specifically designed to perform local
control and in parallel, gather and relay information to SCADA or the cloud where it can be analysed and trended, providing operators with the information they need for efficiency management and asset management in addition to real-time control.
Ovarro
www.ovarro.com
Instrumentation Monthly June 2021 47
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