A wave trap is a device for isolating the carrier channel from certain detrimental conditions found in the power and to isolate carrier channels from one another to prevent interference. To accomplish this isolation, the trap must have an impedance at carrier frequencies and negligible impedance at power frequency.
Wave traps are installed in series with the power line conductors and therefore, must carry the power-frequency current that is present.
Line Trap has following Components.
1. Main Coil : Used to provide required inductance.
2. Bird Cage : Used to protect against Birds.
3. Tuning Device : Used to program to block Selected High Frequency Signals.
4. Protection Device : Protection against High Voltage Hazardous.
Line Traps are categorized into Two groups based on installations.
1. Mounted Line Traps.
2. Hanging Line Traps.
Mounted Line Traps are placed over CVT. Normally Line Traps with inductance less than 0.5mH fals under this category. Min reason behind it is actually the weight of Line Traps falls under allowable sustainable weight of CVT.
Lower the inductance lower the frequency band it offers. Which means in order to provide high bandwidth higher inductance is required such between 0.5mh – 2mH. As we all know for such high inductance size of coil increases, which in result increases the weight of Line Trap. These Higher weights Line Traps having weight more than sustainable capacity of CVT say 450 kg, a set separate insulator poles are installed to bare the Line Trap weight.
2. Hanging Type Line Traps are used where a parallel connection on any Transmission Line is practiced. This parallel path provides an additional path to High Frequency Signal, resulting in Loss once reached this new Substation. In order to block PLC Signal from propagation Line Traps are hanged over Transmission Lines as shown in figure.
Classification based on Frequency Band
Based on Frequency Band Line Traps are divided as follows.
1) SINGLE FREQUENCY TRAPS
2) TWO FREQUENCY TRAPS
3) BROAD BAND TRAPS: – The broad band traps comes in two categories, classified as fixed wide band and adjustable wide band.
i. Fixed Wide Band:-
Most wide band are fixed wide band traps, either to the appropriate geometric mean frequency to obtain maximum band width in the upper portion of the carrier frequency spectrum or to another geometric mean frequency specified for certain application.
ii.Adjustable Broad band Traps:
This type of tuning provides an adjustable tuning range and a selection of impedances. It also offers higher impedance than the fixed wide-band tuning.
Adjustable wide band wave traps are finding increasing use because their wider band width combined with a choice of blocking impedance means easier application and less re-tuning resulting from changes in user’s frequency.