RFL offers a wide range of coupling equipment for a complete Power Line Carrier solution, including Line Tuners and Line Traps. Click here for information on Hybrids.
Coupling Equipment
About Coupling
The necessary isolation of a line section at carrier frequencies used for communication is accomplished using coupling equipment, such as by a line inductor connected in series with the line. It is usually tuned to form a line trap, so that it presents a high impedance over a band of frequencies which may be either narrow or wide.
Separation of the power-frequency energy from the carrier-frequency band is accomplished with the coupling capacitor, and the function of the line-tuning unit is to cancel the reactance of the coupling capacitor to achieve optimum impedance matching and power transfer of the carrier signal to and from the transmission line. The line-tuning unit may also tune out the reactance of the coupling capacitor over either a narrow or a wide band of frequencies.
Line Tuners
Line-tuning units, like the trap, may be resonant with the coupling capacitor at either one or two specific frequencies, or across a broad band of carrier frequencies. Frequently, the coupling capacitor and line-tuning unit form a highpass filter. The filtering required is very simple, but the tuning unit will have to pass carrier signals at powers up to 100 watts, and must usually be equipped with a drain coil, surge protector, safety shorting switch, etc. The tuning unit is normally located close to the coupling capacitor in the switchyard, and must be weatherproof. For phase-to-phase coupling, it's common to employ two line-tuning units, driven by a suitable push-pull transformer.
The RFL 9512 Line Tuner matches the impedance of the Power Line Carrier (PLC) terminal to the high voltage power line in order to reduce the insertion loss of the transmission of PLC signals over the power line. In addition, isolation from the power frequency voltage and transient overvoltage protection is provided.
The RFL 9512 Line Tuner is available for Phase-To-Ground or Phase-To-Phase Coupling.
Line Traps
Line Traps, also known as Wave Traps, are a critical part of Power Line Carrier communications.
A line trap is a large inductor, capable of continuously handling high values of power-frequency current, and rugged enough to withstand the stresses of higher current surges. It ranges in inductance from about 0.265 mH to about 3 mH. While large inductances are very expensive, smaller values do not normally have sufficient reactance to decouple adequately at lower PLC frequencies; so it is common practice to tune the line inductor with a tuning pack, which may form a resonant trap at one or two specific frequencies for narrow channels, or which may present an impedance of 400 to 600 ohms over a broad band of PLC frequencies. While narrowband traps are largely reactive, broadband traps are largely resistive within the resonant band, and thus they provide assurance against unwanted resonance with unpredictable reactance of the station bus or other line section.
