Not so very long ago, there was little demand for low-voltage monitoring and control. The gradual proliferation of distributed resources – particularly wind and solar energy – has changed all that. As a result, distribution utilities find they increasingly need a solution for remote management and monitoring of their MV/LV infrastructure.
The trouble is that most distribution automation systems today use wired connections. Wiring is expensive to install and practically impossible to retrofit. Hence the DSOs’ reluctance to embark on what appears to be a major investment.
The good news is that wireless sensor technology for LV monitoring in an MV/LV substation offers an effective alternative that boasts a number of advantages. I’ll expand on those later.
An MV/LV distribution substation has a number of different communication needs – long distance with the SCADA; inter-substation; intra-substation; link to smart meters – each one supporting various levels of data volume, distance, space and security. Of these communication systems, the one that should be given priority in the transition to wireless technology is the intra-substation communication between the Distribution Substation Unit (DSU) and the LV feeder devices. There are on average 10 feeders of three phases each in the LV pillar; that means 30 or more wires with only 10 cm of space per feeder. It’s not difficult to imagine that this is an overwhelming challenge.
A wireless solution dispenses with the problems of wiring, which reduces costs, time to install and the risk of errors. And those are just the immediate benefits. There are others. For example, a specific tool is available to install the sensors. This means that personnel don’t have to touch the inside of the cubicle, so the procedure can be accomplished – safely – under voltage. Also, when the sensors are plugged in, a software module kicks in automatically to check and display the set-up. And should there be any errors, it automatically reconfigures the mapping to correct them. Furthermore, the risk of disconnection caused by vibrations in the substation is eliminated.
In addition to the above, the flexibility of wireless technology is also an advantage. New feeders can be equipped with sensors practically without limit, whereas with wired connections, expanding the system is limited by the number of terminal blocks in the DSU.
There are essentially no drawbacks. The issue of power supply is solved by the use of self-powered sensors. Cyber security is taken care of through the choice of the right wireless standard. Interference with other devices is also avoided by choosing a wireless standard that selects a free channel.
At Schneider Electric, we have tested a number of wireless communication standards. The one that best fits the requirements is ZigBee PRO Green Power (ZGP), which is common in residential communication systems but a novelty in industrial applications. This is the system that has been integrated in our new range of DSUs, with a ZigBee transceiver function in the DSU and a set of three sensors for each feeder.
The wireless LV current sensor represents the first step in the next generation of sensors.
To learn more, read our technical paper on this topic.