Smart grids turn to wireless systems
As one of the very few smart metering providers, Kamstrup A/S (Skanderborg, Denmark) offers RF-communication in their smart metering system and has done so for more than ten years. Seen from Kamstrup’s point of view, the reason why wireless systems prevail in smart grid technology is simple: RF works – a plain fact which is being corroborated by numerous, high-performing RF-based systems from all over the world.
In the past, Kamstrup offered RF and PLC solutions together, but has now terminated its PLC program as RF very soon began to show much more convincing results. The evidence is plenty.
Sweden was one of the first countries to roll out smart meters nationwide, and now the Swedish case study offers experience to learn from. Many utilities who first opted for a PLC solution have afterwards switched to an RF-solution as PLC showed poor performance on meter readings, of which 60 to 90 percent was traceable to grid disturbances. Some have chosen to mend the problem by installing expensive filters.
Some PLC providers therefore take reservations against grid disturbances when guaranteeing 100 percent performance claiming disturbances to be a separate problem to be dealt with and thus pushing it back to the utility. But the fact is that cables are simply a hard environment for communication. The increased disturbance level in the grid which caused many PLC networks to fail in Sweden could for a large part be traced to the massive exchange of incandescent light-bulbs with low-energy light bulbs.
All electric devices which are connected to the grid are also potential sources of grid disturbance as they not only consume power from the grid, but also return electromagnetic disturbances. The Electromagnetic Compatibility-directive (EMC) regulates how much disturbance electric devices may cause. But even though the equipment which is now causing problems in Sweden may comply with the EMC-directive, it is still liable to influence a PLC-based meter reading system because the communication unit in the meter is affected by the total amount of disturbances generated by all installed equipment in a house. So, when substantial changes happen simultaneously – like the out-phasing of the incandescent light bulb – the meter reading system can be affected in spite of the regulatory fulfillments of the individual product. With the Smart Grid ahead such substantial changes will be even more frequent.
The implementation of renewable energy sources are being followed up by still more electric applications that will have unpredictable influences on the grid. Radio Frequency communication systems are not submitted to the same restrictions as cabled systems are. The wireless technology enables a mesh-system where up to 1,000 meters are mutually connected in networks communicating with one of two concentrators. Power line networks lack the fallback possibility if a communication line is broken or filled with noise. In radio, you will have hundreds of alternative routes handled automatically by the network as it is not stuck with the physical wires.
The Radio Mesh Network is composed exclusively of meters and concentrators so there is no extra infrastructure to build up in radio solutions. All meters also act as repeaters for the radio mesh network. Formerly, RF-communication was handicapped by short range and expensive antenna installations at the metering points. At the same time, the communication was confined to license free bands which often raised the question of interference problems. This has practically never been a real problem, but it could arouse some skepticism towards RF.
Some years ago, Kamstrup decided to use licensed frequency bands for the routing communication between the meters. These licensed bands are country specific and often reserved for specific purposes like meter reading which eliminates interference and opens up for the use of a much higher transmission power than in license free bands. The higher power results in higher stability in the meter readings and a considerably longer range, with compact internal antennas.
About the author:
Gert Skriver is Corporate Editor at Kamstrup A/S (Skanderborg, Denmark), a manufacturer of system solutions for smart energy and water metering. He can be reached at ges@kamstrup.dk
Visit www.kamstrup.com.
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