How to efficiently use the electrical distribution underground cables for Power Line Communications and to achieve the Smart grid’s goals.

Energy Smart Grids

Spain

Data transmission over power distribution cables is now possible thanks to the medium voltage PLC coupling units.

This type of communication is known as Power Line Communications (PLC) or Broadband over Power Line (BPL).

Different types of couplers allow the physical connection of the modems to the power lines to be carried out, achieving the required electrical security and safety for the communication equipment.

There are two main technologies for couplers: capacitive and inductive.

The coupling capacitor (Ca) offers high impedance at power frequency (50 or 60 Hz) and low impedance at the high frequencies used by the PLC modems.

The LC tuning elements and the transformer are used to match the line and modem impedances, minimizing the coupling losses and increasing the performances of the PLC link.

Capacitive coupling

Capacitive couplers are based on the following schematic:

PLC coupler schema

Inductive couplers are based on the electromagnetic induction principle, acting as toroid signal transformers. The couplers have usually N:1 ratio, and transmits through the cable conductor or through the ground connection of the underground cables sheath.The sheath-transmitting couplers can be non- intrusive or intrusive couplers, depending on the installation method: clamping the sheath or connecting among the sheath to ground connection respectively.In the pictures are shown the inductive principle of the conductor’s inductive coupler s and two different installed ZIV couplers.

Over conductor inductive transmission principle

PLC link attenuation

Different tested capacitive couplers

Using the proposed couplers in the Estabanell MV gridBroadband PLC links are used as network backbone. They are currently being installed in order to develop the Transformer Centers’ automation network, including Fault Detectors (DPF), Smart Metering, CCTV, etc..., and to create the basement for the future SmartGrid.

The measured attenuation is in the 30 – 40 dB range, which allows speeds as high as 20 Mbit/s to be achieved.

The reached speed is enough to provide different SmartGrid services such as telecontrol, fault detection and automatic metering reading among others.

When over-conductor inductive couplers are used, the MV / LV transformers’ impedances (Zt) at both ends of the link close the communications path, implementing a loop through the toroid couplers, and therefore allowing the transmission of the HF signals from the modem to the line.

Inductive couplers are very easy to install and can be used in those locations where the installation of capacitive couplers is not possible due to the limited available space.

As a result of our tests the best performances in our MV network are achieved by means of capacitive couplers.

Second choice is the “intrusive” inductive devices, which use the grounded sheath of the MV cable as transmission support.

Behavior of couplers during a transient over the MV gridMV grids are the common way for transmitting electrical power and telecommunications signals (PLC).Therefore, couplers aren’t immune to the transients produced during electrical failures of any kind.

We are currently installing and testing the “intrusive” inductive couplers on distances over three kilometers and with Spread Spectrum PLC achieving a safe and efficient complement to the main communication network.

Illustration path overcourrent produced by lightning (Source Electricidad Aplicada)

Smart Grid

Communications technologically

efficient

Improve return on

invesments

improved data

security

Independence from

communication suppliers

Conclusion:

The achievedperformancefacilitates:

José Antonio Moreno j.moreno@ziv.es

Ramon GallartRGallart@estabanell.cat