Line traps are connected in series with HV transmission lines. The main function of the line trap is to provide a high impedence at power-line-carrier frequencies (30-500 kHz) while introducing negligable impedence at power frequency (50 or 60 Hz).
The high impedence limits the attenuation of the carrier signal within the power system by preventing the carrier signal from being: – dissipated in the substation; – grounded in the event of a fault outside the carrier transmission path; – dissipated in a tap line or a branch of the main transmission path.
Up to kA rms
short circuit current
manufactured for Trench line traps
Line traps are installed in the HV transmission lines and can be mounted in various pedestal or suspension configurations.
Power Line Carrier [PLC] is a common method of Power System Communication such as teleprotection and voice and data communication, it has a reputation as being one of the most economical and reliable forms of communication, and for being versatile in its application. A basic PLC system consists of three distinct components:
- signal carrying medium [HV transmission line)
- communication apparatus [transmitters, receivers and associated components)
- coupling/blocking equipment such as coupling capacitors [CC), capacitive voltage transformers [CVT), line tuners [coupling devices) and line traps
Line traps are connected in series with HV transmission lines. The main function of the line trap is to present a high impedance at the carrier frequency band while introducing negligible impedance at the power frequency. The high impedance limits the attenuation of the carrier signal within the power system by preventing the carrier signal from being:
- dissipated in the substation
- grounded in the event of a fault outside the carrier transmission path
- dissipated in a tap line or a branch of the main transmission path
Types of tuning
Single Frequency Tuning lf narrow blocking bands are required, single frequency tuning is the simplest and most economical type of tuning available. Within the narrow band, high blocking impedance can be provided resulting in excellent PLC signal isolation.
Double Frequency Tuning
The double frequency tuning arrangement blocks two relatively narrow bands of frequencies. Otherwise, the blocking characteristic is similar to single frequency tuning. For proper operation and isolation of the tuned bands, a minimum frequency separation must be maintained between the peak tuning frequencies. The frequency must be a minimum of 25 kHz or 25% of the upper tuning frequency peak.
Wideband tuning is the most common type of tuning as it efficiently utilizes the main coil inductance. Wideband tuned line traps are suitable for multi-channel applications, since relatively constant impedance is obtained over a broad frequency range. This type of tuning provides high bandwidth flexibility for future changes or expansion of PLC frequencies. PLC channels can be placed anywhere within the blocked bandwidth.
Self-tuned Line Traps
Self-tuned line traps do not require tuning. The blocking characteristic is achieved by simply utilizing the self-capacitance of the main coil winding. The inductance of a self-tuned line trap is higher than a tuned line trap.
Mounting and connection
Trench line traps can be mounted in several configurations. Suspension mounted line traps are available with either single point or multi-point suspension brackets. Line traps can also be pedestal mounted directly onto coupling capacitors [CCs), capacitive voltage transformers [CVTs) or station post insulators. Trench offers several types of mounting pedestals:
- single insulator support pedestal
- multi-insulator support pedestal
- insulated pedestal
Other than the insulated pedestal, all pedestals are electrically connected to the lower terminal of the line trap and can be used as both the electrical and mechanical connection to the CC or CVT. lf necessary, the upper line trap terminal can be utilized as the connection to the CC or CVT. A pedestal insulated from the bottom end [bottom spider) of the line trap must be used in conjunction with a special insulated connection rod supplied by Trench.
Pedestals are standardized but can be custom made to suit customer requirements. Terminals supplied on the line traps can be either pad or stud type according to IEC or NEMA standards.