Data Concentrators and Telecom Gateways enable digital grids

Power Line Communications (PLC) have been widely adopted in many smart meter roll-outs where medium voltage (MV)/ low voltage (LV) transformers in Secondary Substations (SS) feed a large quantity of meters. This is  common for the grids in Europe. The network architecture of PLC-based metering system is different from the architecture of a RF-based system, or a metering system that relies on the telecommunication services provided by public cellular network operators.

As the telecommunication media are the power cables, smart meters connectivity depends on the LV grid topology. This implies that all smart meters attached to each LV grid segment that is linked to a MV/LV transformer naturally form a telecommunication subnetwork that is managed by the equipment installed in the SS.

Data concentrators installed in SS not only play a key role in any smart metering architecture but also are a key component for grid monitoring applications.

If we examine a PLC data concentrator, this complex device integrates several functions.  Firstly, several telecommunication technologies are supported. On one hand, a PLC coordinator or base node is responsible for managing the PLC subnetwork and providing secure telecommunication services to all smart meters attached to this subnetwork. On the other hand, it integrates a cellular interface so that a continuous connection is guaranteed to the central system.

To ensure this continuous connection, some data concentrators manufacturers, such as ZIV, add  the capability to its devices to set up an alternative connection through a backup public network operator so that whenever a network problem arises with the main public network operator, the connection with the central system is not lost, thanks to the backup operator. Secondly, a task scheduler is also included so that data can be regularly gathered from the smart meters (based on open protocols such as DLMS) and stored internally. All this data is delivered at scheduled times to the central system using web services. Additionally, either on demand requests coming from the central system or important spontaneous events delivered by the smart meters will be serviced based on their priorities.

Data concentrators monitor voltage and current levels at the LV side of the MV/LV transformer and additional monitoring of other parameters, such as power quality and service continuity. Besides, they can also detect faults and, in certain grid topologies, even MV high impedance faults. Both features, monitoring and fault detection, make of the data concentrator a key component in the new digital grid.

Certain Utilities consider that not all secondary substations require a data concentrator. Nevertheless, it’s important for them – due to economies of scale – to maintain the PLC telecommunication interface to all their smart meters. Those Utilities rely their smart metering architecture  on telecommunication gateways.As depicted below, telecommunication devices do not have to include either temporary data  storage or grid monitoring features. Such devices are plain telecommunication devices that integrate both, a PLC coordinator/base node and a cellular interface to ensure a continuous connectivity to the central system. It should be highlighted that PLC gateways do not need to be installed in secondary substations. They can be installed in different locations on the LV grid.  For instance, they may be installed in the LV fuse boxes, that are the boundary of the Utility’s private distribution network or even close to the smart meters. In this way, this device provides flexibility for many smart meter roll-outs allowing it to cope with difficult installation sites at a very reasonable cost.

An important component when deploying a smart metering infrastructure based on telecommunications gateways is the so-called virtual data concentrator. This Software component, that is installed in the Utility’s data center, is responsible for gathering the data from all smart meters accessible through the telecommunication gateways. In terms of telecommunication protocols, the virtual data concentrator accesses all the smart meters using the well-known DLMS protocol, which demands higher data usage to gather all metering data values. As telecommunication gateways do not provide temporary data storage, metering data availability greatly depends on the telecommunications network reliability. For this reason, features such as dual SIM for assuring a continuous link with central system are mandatory. Also, it is very important to know the connectivity status with all the smart meters attached to the subnetwork created by the telecommunication gateway. To do so, PLC technologies such as PRIME (http://www.prime-alliance.org/) have internal mechanisms (ALIVE messages) that are regularly exchanged between the telecommunication gateway and every smart meter in the subnetwork.