# Wave trap is used to trap waves of

Wave trap is used to trap waves of

### Right Answer is: Higher frequencies entering generator or transformer units

#### SOLUTION

Wave trap is a parallel tuned inductor-capacitor tank circuit made to be resonant at desired communication frequency. The parallel tuned wave trap is connected in series with the load and is tuned to resonate at the unwanted frequency, so it presents a high impedance to this current component. A wave trap is a device that allows 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 allows only 50 Hz signal to pass through it.

Since the power transmission lines physically go between substations themselves, it is possible to use this metallic link as a communications line also. The figure shows a line between substations with a wave trap at each end.

The wave trap is nothing more than a parallel tuned inductor-capacitor “tank” circuit made to be resonant at the desired communication frequency. A coupling capacitor installed on the line side of each wave trap allows the communications signal to be superimposed onto the power conductor. If the frequency of the communications signal is 250 kilohertz (kHz), the tuned wave traps on each end will effectively block the signal from passing through them onto the substation bus and into transformers and other transmission lines.

Several lines between substations can have the frequency of their own communications and therefore do not interfere with each other. The impedance of the parallel tank circuit is almost nil at the power line frequency of 50 Hz and, therefore, very little power loss is experienced in the wave trap. On the other hand, the impedance of the coupling capacitor at 50 Hz is very high, so the power frequency current does not cause a phase-to-ground fault. At the same time, the impedance of the coupling capacitor at the communications frequency (250 kHz in this example) is very low; therefore, it does not take a very powerful transmitter to place the signal on the overhead power conductor.

Wave traps are used to prevent carrier current from entering the power equipment in the sub-station. The wave trap also reduces cross-talk with other PLC circuits connected to the same station.

One disadvantage of power line carrier applications is that a fault inside the protected zone may also short-circuit the communications channel. If a communications channel itself becomes faulted, the impedance relays may operate incorrectly during a fault or even operate when there is not a fault.

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