Komunikasyon sa Carrier ng Linya ng Kapangyarihan | PLCC

Tinatawag din itong wired wireless, ang Power Line Carrier Communication (PLCC) ay lumago nang malayo mula sa kanyang pinakaunang paggamit sa pagsukat sa mga malalayong lugar hanggang sa kanyang kasalukuyang mga aplikasyon sa home automation, high speed internet access, smart grid atbp. Noong maagang bahagi ng ika-20 siglo, ginamit ng mga kompanya ng kuryente ang telepono bilang medium ng komunikasyon para sa pagpapadala ng mensahe ng boses para sa operasyonal na suporta, maintenance, control atbp. at bilang isang paraan ng koneksyon sa mga malalayong lugar. Ang mga linya ng telepono ay tumatakbo parehistro sa mga power lines. Ito ay may maraming di-pabor:

• Ang paggamit ng mga telephone circuits sa malalayong distansya at sa mahirap na terreno tulad ng mga bundok ay napakamahal.

• Noise interference dahil sa currents na umuusbong sa parallel power lines sa mga telephone circuits.

• Mabilis na shutdown ng mga telephone cables sa matinding kondisyon ng panahon tulad ng yelo sa taglamig, bagyo atbp. na nagpabawas ng reliabilidad nito.

Ito ang nag-udyok sa ideya ng pagbuo ng mas robust at mas mura na paraan ng komunikasyon. Ang paggamit ng power line bilang paraan ng telephony ay isang matagal nang ideya at ang kanyang unang matagumpay na test ay naganap sa Japan noong 1918. At pagkatapos nito, nagsimula ang kanyang komersyalisasyon noong 1930s.

Power Line Carrier Communication

Ang figure 1 ay nagpapakita ng isang basic PLCC network na ginagamit sa mga power substations. Ang Power line carrier Communication (PLCC) ay gumagamit ng umiiral na power infrastructure para sa transmisyon ng data mula sa sender hanggang sa receiver. Ito ay gumagana sa full duplex mode. PLCC system binubuo ng tatlong bahagi:

1. Ang terminal assemblies kasama ang receivers, transmitters, at protective relays.

2. Ang coupling equipment ay ang kombinasyon ng line tuner, coupling capacitor, at ang wave o line trap.

3. Ang 50/60 Hz power transmission line ay nagsisilbing daan para sa pagpapadala ng data sa PLCC bandwidth.

Coupling Capacitor

It forms the physical coupling link between transmission line and the terminal assemblies for the relaying of carrier signals. Its function is to provide high impedance to power frequency and low impedance to carrier signal frequencies. They are usually made up of paper or liquid dielectric system for high voltage application. The ratings of coupling capacitors range from 0.004-0.01µF at 34 kV to 0.0023-0.005µF at 765kV (source: IEEE).

Drain Coil

As shown in the figure 1 the purpose of drain coil is to provide high impedance for carrier frequency and low impedance for power frequency.

Line Tuner

It is connected in series with the coupling capacitor to form a resonant circuit or carrier signal frequency high pass filter or band pass filter. Its function is to match the impedance of the PLC terminal with the power line in order to impress the carrier frequency over the power line. In addition it also provides isolation from power frequency and transient overvoltage protection.

Line Trap or Wave Trap

It is a parallel L-C tank filter or band-stop filter connected in series with the transmission line. It presents high impedance to carrier signal frequencies and very low impedance to the power frequency. It consists of

1. Main coil

   An inductor that is connected directly to the high voltage power line carries power frequency.

2. Tuning device

   It may be a capacitor or a combination of capacitor, inductor and resistor, connected across the main coil in order to tune the line trap to the desired blocking frequency.

3. Protective device

   It is usually a gap type surge arrester used to protect the line trap from damage due to transient over-voltages.

The line trap or wave trap prevents unwanted loss of carrier signal power and also prevents carrier signal transmission to adjacent power lines. Line traps or wave traps are available for narrow-band and wide-band carrier frequency blocking applications.

Power Line Channel Characteristics

• Characteristic Impedance

  The characteristics impedance of transmission line is given by :
  
  Where, L is the inductance per unit length in Henry(H).
  C is the capacitance per unit length in Farad(F).
  It varies in the range of 300-800 Ω for power line communication.

• Attenuation

  It is measured in decibels(db). Attenuation losses can be due to the impedance mismatching, resistive losses, coupling losses and various other losses that occur in the line trap, line tuner, power line etc.

• Noise

  The signal-to-noise ratio(SNR) must be high at the receiving end, otherwise the carrier frequency shows erratic patterns at the receiving end. The noise level limits the attenuation that PLCC channels can tolerate.

• Bandwidth

  The wider bandwidth