Power Line Communication Degradation caused by Surge Protective Devices

Abstract

We have already reported^(3)-(6) that the capacitance of Surge Protective Devices (SPDs), such as varistor type SPDs, degraded the transmission rate of power line communication modems. Not only the capacitance of the varistor but also the inductance of the varistor and wiring of SPD cause LC series resonance and attenuate signal level at the resonant frequency. In this paper, we found that there is a close relationship among capacitance, maximum current, size of disk, and varistor voltage. The inductance is the sum of SPDs themselves and wiring connecting SPDs to AC power lines. Therefore how to install SPDs and connect them to Protection Earth (PE) is important. Typical varistor type SPDs that have 1000pF to 14000pF and wiring less than 50cm will have resonant frequency somewhere between 2MHz to 30MHz. We propose practical information to select and install SPDs on AC power lines, and to estimate PLC signal degradation.