Line Matching Unit
The Line Matching Unit matches the impedance of the Power Line Carrier (PLC) terminal to the Impedance of the high voltage power line in order to reduce the insertion loss for the transmission of PLC signals over the power line. In addition, provide isolation from the power line and protect from transient overvoltage.
This LMU is used with PLC communication systems connected to coupling capacitors having a capacitance between 1,400 & 25,000 pF.
All of the characteristics of the LMU conform to the requirements of IEC 481-74 (Coupling devices for Power Line Carrier systems). The peak envelope power (PEP) can be supplied with rating of 400. 600, 800, and 1000 Watt.
The LMU is used for phase-to-phase coupling. Phase-to-ground and three phase versions are also available. Commissioning is simplified since no adjustments are necessary.
The high-pass or band-pass circuit consists of a drain coil, inductors, and capacitors. A matching Transformer provides potential insulation between line side and equipment (cable) side and provides the means to make the power line impedance match that of the PLC terminal. The power frequency current derived from the coupling capacitor is drained to ground by the integrated drain coil.
Limitation of voltage surges coming from the power line at the terminals of the tuner is performed by a lightning arrester connected in parallel with the drain coil. The line tuner will be short-circuited to ground when the grounding switch is closed.