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FAQ Frequently Asked Questions Ground Connections Two different ground connection systems What would happen if the ground connection were eliminated? Conclusions The ground connection is a element very important to guarantee the safety of all the devices installed in the power lines. As a result, this is one of the main issues to be considered during the installation of the couplers. The Capacitive Couplers for medium voltage power lines are used for the transmission of PLC-BPL signals on a frequency range from 2 to 100 MHz. The couplers have two different ground connections (the connection to the ground and the shield of the coaxial cable), so the installation of a coupler could, in some cases, involve two different ground systems. Some particular situations must be considered when we install a coupler. This paper has been prepared to give an answer to several questions received about what would happen if we eliminate the ground connection of any of the Capacitive Couplers, once they are installed. Two different ground connection systems ARTECHE Capacitive Couplers for medium voltage power lines used for the transmission of PLC-BPL signals are made up of a silicone module that houses the capacitive part and that provides the necessary electrical insulation, and a polyurethane plastic element which houses the tuning circuitry together with the ground connections and the TNC/BNC connector for the signal cable. The next picture/diagram shows the scheme of the internal configuration of the capacitive couplers (Pic.1). Pic. 1 In the installation of the capacitive couplers, two different grounds must be considered: When the ground references are the same, the whole ground system will be always at the same voltage. (1) The one connected by the ground screws of the coupler that is the ground connection of the power line to which the coupler must be connected to get a reference for the high voltage circuit. Otherwise, if the ground references are different, a voltage difference could appear between the two different ground systems, due to failures in elements in the power line or to the working conditions of the lightning arresters. (2) The ground of the coaxial cable connected to the TNC/BNC connector that corresponds to the shield of the coaxial cable. This shield should be grounded at the PLC-BPL repeater. In this case the capacitive coupler is an element connected to these two ground systems, so it is the device that should withstand this difference of voltages. To protect the device in this situation, the coupler has been designed to withstand a 5 kV insulation between the ground connections and the TNC/BNC signal connector. Depending on the situation in field and on how the distribution network has been designed, both ground connections could be connected to the same ground reference or to different ones. Ground connections www.arteche.com 1 FAQ Frequently Asked Questions What would happen if the ground connection were eliminated? On the side of the TNC/BNC connector, there is 0 Volts, because of the ground connection of the coaxial cable in the PLC-BPL repeater. If a capacitive coupler or any electrical device losses the ground reference, the working conditions of the device are different from the ones defined as normal working conditions. These situation should not happen because the device is not prepared to withstand the ground reference disconnection. The transformer insulation works up to 5 kV because it has been designed to withstand temporary overvoltages but not the voltage generated because of the elimination of the ground connection. Thus, the transformer will not withstand this voltage. Let’s see what would happen in this situation (Pic. 2): The ground reference is lost, so the whole system will be at V volts (the voltage of the line) on the side of the drain coil because of the voltage of the power line. The transformer will fail and the coupler will stop working in communications because of that. Pic. 2 This situation will provoke the following scenario (Pic. 3): ground but if the coaxial cable is disconnected from the PLC-BPL repeater, the ground reference will be lost again and a risky situation will come up. The system suddenly will have a new ground reference through the TNC/BNC connector and the coaxial cable connected to the PLC-BPL repeater. This connection maintains the reference of the system. In this case, if the coaxial cable has an extra ground connection (coax grounding block) before being connected to the PLC-BPL repeater, this will avoid possible risks for the people working in the PLC-BPL repeater. The voltage on the coaxial cable connected to the PLCBPL repeater will not be so high while it is connected to Pic. 3 Ground connections 2 www.arteche.com FAQ Frequently Asked Questions Conclusions The ground connection is a very important element in any power line to guarantee the coupler’s normal and safe working conditions and that can not be eliminated. The electrical safety of the device will depend on this connection. ARTECHE capacitive couplers have two different ground connections, one is the connection to the ground the coupler, grounded by a direct connection to ground and the other one is the shield of the coaxial cable, grounded at Ground connections www.arteche.com the PLC-BPL repeater. ARTECHE capacitive couplers have an internal 5 kV isolation to withstand the possible overvoltages between the two different ground connections. In every device connected to a voltage power line could happen the same. If the ground connection is removed, the working conditions and the safety of the entire system would change and a significant failure could happen. 3