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This type of protection is used for protection of transmission lines. Carrier current
frequency ranges from 35kHz to 500kHz are transmitted and received through the
transmission lines for the purpose of protection.Each end of the line is provided with
identical carrier current equipment consisting of transmitter, receiver, line – tuning
unit, master oscillator, power amplifier etc. The carrier equipments is connected to the
transmission line through “Coupling capacitor” which is of such a capacitance that it
offers low reactance to carrier frequency but high reactance to power frequency.
Thus coupling capacitor allows carrier frequency signals to enter the carrier
equipment. A line trap unit is inserted between bus bar and connection of coupling
capacitor to the line. It offers low impedance to 50Hz and high impedance to carrier
frequencies. This unit prevents the high frequency signals from entering the
neighboring line, and carrier currents flow only in the protected line.
Frequencies between 50 to 500 kHz employed in different frequency bands through
transmitter carrier frequencies are generated in oscillator. The oscillators can be tuned
to a particular frequency selected for the application. The output of the oscillator is
fed into the amplifier to overcome the losses in the transmission path between the
transmitter and the receiver at remote end of the line.
The high frequency signals arriving from remote end are received by receiver
Receiving unit comprises an attenuator, which reduces the signals to a safe value.
Band pass filter, which restricts the acceptance of unwanted signals. Matching
transformer or matching elements to match the impedances of line and receiving unit.
Different frequencies are used in adjacent line sections. The choice of frequency
bands for various sections should be coordinated. The modulator, modulates 50Hz
gregorymasila answered the question on February 20, 2018 at 16:16
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