PLCC Connections and Wave Trap in Substations

PLCC Connections

PLCC, Power Line Carrier Communication, is an approach to utilize the existing power lines for the transmission of information. In today’s world every house and building has properly installed electricity lines.

By using the existing AC power lines as a medium to transfer the information, it becomes easy to connect the houses with a high speed network access point without installing new wirings.

This technology has been in wide use since 1950 and was mainly used by the grid stations to transmit information at high speed. Now a days this technology is finding wide use in building/ Home automation as it avoids the need of extra wiring. The data collected from different sensors is transmitted on these power lines thereby also reducing the maintenance cost of the additional wiring. In some countries this technology is also used to provide Internet connection.

Wave trap in Substations

• Wave trap is a parallel tuned inductor - capacitor tank circuit made to be resonant at desired communication frequency . It reduces corona losses in transmission lines in power system.
• Wave trap is installed in the substation for trapping the high frequency communication signal sent on the line from remote substation and diverting them to the telecom panel in substation control room. These high frequency signal should not be coming on the buses as these may damage the equipment's .
• A wave trap is a device that allow only a particular frequency to pass through it that it filters the signals coming on to it . So a wave trap is connected between buses and the transmission line which allow only 50 Hz signal to pass through it.
• This is relevant in power carrier communication (PLCC) system for communication among various substation without dependence on telecom company network . The signals are primarily teleportation signal and in addition , voice and data communication signal.

Wave Trap is a basket looking coil having high inductance. It is used in  Power Line Carrier Communication (PLCC) system of substation. The wave trap is put in use along with a coupling capacitor or a capacitor voltage transformer (CVT) both of which possesses high capacitance value. It has to be kept in  mind that Inductive reactance (2*Pi *f*L) goes high when the value of frequency (f) is high whereas Capacitive reactance (1/2*Pi *f*C) goes low when the frequency is high and vice versa. Any substation is connected with another substations through power circuit / transmission line. . Now in order to improve communication between two substations connected with transmission line, PLCC system has been invented keeping in view that already there is a hard wire connected between the two stations. The Power circuit works on 50Hz frequency and the communication circuit works on High frequency of mega hertz value. So there is no chance of interference or cross over between them. Now the problem was that how to physically separate those two frequencies where 50 Hz frequency with high voltage level should not enter the communication panel and at the same time Mega Hertz frequency should not enter the circuit breakers or transformers. Here the wave trap is used along with CVT. The power line carrying both the frequencies is connected in series with wave trap enroute to circuit breaker. Through the wave trap power circuit finds no problem to pass through it but the high frequency communication wave cannot pass hence gets blocked there. Before the wave trap a bypass route is given to this high frequency through CVT and the out put wave is sent to Panel. Thus wave trap is used for blocking or trapping the high frequency waves from entering the power circuit.