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Wave traps (high-frequency stoppers)

Wave traps or line traps (high-frequency stoppers) are maintenance-free parallel resonant circuits, mounted inline on HV AC transmission power lines to prevent the transmission of high frequency (40 kHz to 1000 kHz) carrier signals of power line communication to unwanted destinations. Line traps are cylinder-like structures connected in series with HV transmission lines.

132 kV, 220 kV and 400 kV substation equipment and details
132 kV, 220 kV and 400 kV substation equipment and details

The wave trap acts as a barrier or filter to prevent signal losses. The inductive reactance of the line trap presents a high reactance to high-frequency signals but a low reactance to mains frequency. This prevents carrier signals from being dissipated in the substation or in a tap line or branch of the main transmission path and grounds in the case of anything happening outside of the carrier transmission path.

The line trap is also used to attenuate the shunting effects of high-voltage lines.

The wave trap consists of three major components: the main coil, the tuning device, and the protective device (also known as a surge arrester). The protective and tuning devices are mounted inside the main coil. A line trap may be covered with a bird barrier, in which case there are four components. The main coil is the outer part of the line trap which is made from stranded aluminum cable.

The reactor coil, depending on the device, can be made up of several aluminum wires, allowing equal distribution amongst the parallel wires. The next major component is the tuning device. This device is securely installed inside the main coil. It adjusts blocking frequency or bandwidth, and consists of coils, capacitors, and resistors.

This smaller coil is attached to both ends of the main coil.

Power Line Carrier Communication (PLCC) scheme
Power Line Carrier Communication (PLCC) scheme

Its purpose is to create a blocking circuit which provides high impedance. There are three types of tuning devices: wideband tuning, single frequency tuning, and double frequency tuning. The tuned circuit is usually a dual-circuit broadband type.

If the traps are self-tuned, they do not require the use of any tuning devices. With the use of a tuning device, a line trap can be tuned to a frequency of 1000 Hz. The last main component is the protective device, which is parallel with the main coil and the tuning device. It protects the main coil and the tuning device by lowering the over-voltage levels.

The bandwidth of a line trap is the frequency range over which the line trap can provide a certain specified minimum blocking impedance or resistance.

Line traps are connected in series with power line and thus their coils are rated to carry the full line current. The impedance of a line trap is very low at the power frequency and will not cause any significant voltage drop. In order to communicate, high-frequency line traps are used as they allow substations to communicate with each other through the power lines at the same time as they transmit electrical power.

In order to separate power from messages being sent, different frequencies are used. Electrical power has a frequency of 50 Hz or 60 Hz in most places, and the communication waves use frequencies such as 150 kHz and 200 kHz. Line traps consist of filter circuits that allow only power frequency waves to travel to that of electrical equipment.

They also stop communication waves from traveling to equipment. Communication is crucial for substations.

Title:132 kV, 220 kV and 400 kV networks and substation equipment – Ankur Paul at Department of Electrical Engineering, Girijananda Chowdhury Institute of Management and Technology (GIMT)
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132 kV, 220 kV, 400 kV grids and substation equipment for engineers beginners
132 kV, 220 kV, 400 kV grids and substation equipment for engineers beginners

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More Information


  1. GREEN Singoyi
    Feb 16, 2023

    Kindly arrange to provide the LIST of equipment that is required to lay and install the 132KV Overhead Transmission Line including mounting of the monopoles and other related line hardware.

    Looking forward to hearing from you.


    Aug 05, 2022

    Dear Sir

    Kindly answer Me Why 33 kv/415v Line more voltage fluctuation than 132 kv/33kv line even for both environment condition is same.

  3. Salim Shihab
    Jan 23, 2021

    We have been offered a supply for Line traps, we requested the frequency range to be 40-500Khz, the supplier mention that it is not possible to supply Line trap with this frequency, I need a clarify for the reason please.
    Our request was for 132kv substation with these specs:
    Continuous current =1600 Amp
    Short time current = 40/1 sec.
    Inductance at 50 HZ = 0.5 mh.
    Blocking impedance = 800 Ω.

  4. Tanveer Ahmad
    Apr 06, 2020

    We are looking for supply and purchase material, tools equipment for a 132 kg Grid station project , list will be provide through email . before purchase rate of each items according to list will be proved by supplier, place to deliver will be pakistan punjab province

    Contact Details
    Project Manager
    Email: [email protected]
    Name: Tanveer Ahmad
    Company Name: PEC
    Country/Region: Pakistan

  5. Laxmi B Shilpakar
    Apr 06, 2020

    I want to read materials related to the training materials on the subjects of Substation and Generator protection.

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