We all know that power transmission lines are used to carry electrical power from one end to another. It is majorly carried out with the help of substations.
But, do you know that these power lines can also carry communication signals apart from standard power signals? So, related to this concept, there is one important device used in electrical substations for helping this concept work properly. This device is called a wave or line trap.
In this post, we will learn the concept related to a wave trap.
Power Line Carrier Communication (PLCC)
First of all, let us, first of all, understand how we can transfer power and data communication in a single cable. This technique is called Power Line Carrier Communication (PLCC).
When you are transmitting and receiving data through power lines, you will require PLCC transmitters and receivers at both ends to communicate properly.
Basically, the normal data voltage is modulated to a very high frequency and superimposed on a standard low power frequency (in India, it is standard 50 Hz).
Due to superimposing, two separate frequencies can travel at the same time in the same line. When it is received at the PLCC receiver, the data frequency is separated from the power frequency and we can thus use the final received output then. Due to this, we can use both frequencies in the same line.
Wave Trap
Now, let us see a major issue related to this PLCC technique. As we saw, both signals are at different frequencies. The standard power frequency can be a maximum of 60 Hz, but the communication frequency can go up to a maximum of 800 kHz. The equipment used in a substation-like transformer is sensitive and designed only for the operation of up to 60 Hz.
Now, imagine two substations that have a power line in between for power transmission and data communication. When the data from one substation starts to travel and reaches the second substation, it meets various other devices in between apart from PLCC receivers. They can be transformers and other high-voltage switching equipment.
When this signal meets these devices, after a period of the operation time, it can either slowly or instantly damage the devices; as they are designed to operate at standard power frequencies. So, it is necessary that this data signal does not meet these devices and instead, just directly go to the respective communication receivers. For this purpose, a wave trap is used.
A wave trap or line trap is a device that is used to block communication signals from passing through it and only allows power signals to pass through it.
The wave trap acts as a filtering cum protective device that filters the high-frequency signals to low-frequency signal and give protection against surge voltage. You can also call it a frequency stopper.
Wave Trap Connection
A wave trap consists of three major components – the main coil, the tuning device, and the protective device.
The main coil is the outer body of the wave trap. It is directly in interface with the lines above it. It works basically as an inductor inside.
As you know, inductance provides a low-impedance path for current flow. Inductive reactance is directly proportional to frequency.
When the frequency increases, reactance increases. As the reactance increases, the impedance also increases which resists the high-frequency signals from passing through it.
As the power signal has a low frequency, it provides low reactance to them and automatically allows them to pass. So, the output of the main coil will be only a power signal.
The tuning device is installed inside the main coil and is used to tune the main coil to the blocking frequency. The protective device is also present inside the main coil and is used to protect the equipment from surge voltages.
Next comes the coupling capacitor. It works in inverse proportion to the frequency. As the frequency increases, the reactance decreases and it allows them to pass. So, naturally, it will block the power signals from passing through it.
LMU is a line-matching unit. LMU is used as a coupling device and provides proper communication signals with optimum impedance matching, to the PLCC receiver.
Thus, due to this setup, we get low-frequency output at the wave trap and desired high-frequency data signal at the coupling capacitor.
In this way, we understand the concept of a line or wave trap.
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