Everything You Didn’t Know About an AC Line Trap

Have you ever wondered how these huge powerhouses are working to provide us the electricity supply 24X7? You must have seen different sized transformers, electricity poles, and other huge electric wireline arrangements. The electricity that comes to our homes reaches us traveling a long way going through different electrical components and line trap is one of the most significant among them.

The AC line trap is actually a form of ‘parallel resonant circuit’ which is generally tuned to the carrier energy frequency.

A parallel resonant circuit usually has high impedance at the frequency it is tuned with, therefore makes most of the carrier energy to flow nicely toward the remote line terminal. Whereas, the line trap’s coil offers a low impedance path for the power frequency of energy to flow well. As the power flow may get large at times, the coil used in a line trap should also be large in size.

Hence a line trap is inserted between the connection of a coupling capacitor and busbar. It is a parallel tuned circuit made of inductance (L) and capacitance (C).

It has low impedance which can go even less than 0.1 for power frequency (50 Hz) while giving high impedance to the carrier frequency. All in all, an AC line trap maintains a fine difference between the high-frequency carrier signal and the neighboring line. However, the main function of the line trap unit is to deliver high impedance at the carrier frequency band while presenting insignificant impedance at the power frequency. Within the power system, the high impedance actually limits the attenuation of the carrier signal by preventing it from being:

·         Dissipated in the substation

·         Dissipated outside of the main transmission path

·         Grounded in case a fault found outside the carrier transmission path

Following are some of the features of the line trap

Use of special cables and encapsulated design cause low power losses

Designed to meet different technical requirements (mounting, ambient conditions, losses)

Designed to reach ANSI standard C93.3, IEC standard 353, and other international standards

A capacity of 72 kV to 800 kV

200 A to 6500 A

0.1 mH to 4.0 mH

Peak short circuit rating is up to 180 kA

Moreover, there are manufacturers who have more than 50 years of experience in design and manufacturing these AC line traps and there are several approved suppliers for utilities and contractors.

Line traps are widely used in transmission and distribution networks across the globe. It is actually a vital component in power line carrier systems typically used for remote metering, voice communication, remote control signals, and control between substations in the electrical transmission and distribution networks. High voltage transmission lines are often used to transmit carrier signals from 30 kHz to 500 kHz for voice communication, remote metering and protection, and other applications.

Line traps simply stop transmission of high-frequency signals to unwanted directions without loss of energy. Line traps are generally connected to the transmission lines in a series manner and are designed to bear the rated power frequency current and the short circuit current.