We all know that a Harmonic in an electrical term is a sinusoidal term having frequency multiples of its fundamental frequencies (ω). It is generated due to a non-linear load in the power systems. And yes harmonics is bad for the electrical power supply in the system. Power engineers always use a special type of filter/device in order to reduce the harmonics (non-fundamental component).
Let us consider a 3-Φ system, assuming that a-b-c is the phase and Ia, Ib, Ic is the phase current and In is a phase neutral.
From the above expression, we can say that the neutral current (In=0) is when the system is in a balanced or normal condition. It simply means that there is no current present in the neutral line.
Similarly, let us assume in the case of 3rd Harmonics or Triple, the frequency will be three times in all the phases. So, our expression will become:
[Note that here in current Ib & Ic the 360o Phase shift is actually 0o Phase shift]
In this case, we can say that the neutral current (In≠0). It simply means that there is a current present in the neutral line.
From the above expression, it can be concluded that:
- If the sum of three current is not zero, there will be a current and flux present in it. This flux present will link the communication links or lines (due to Magnetic coupling between a power line and a parallel conductor i.e, communication line) and act as interference. Thus, there will be a disturbance in the communication lines whenever it is placed near the power lines.
- If the sum of the three current is zero, there will be no current on the line due to which flux is also absent. Thus, no disturbance or interference will occur when the system is free from the harmonics.
So, I hope it is clear to you regarding the cause of disturbances in the communication lines due to harmonics. If you have any questions and opinions to share, feel free to drop your comments. Thanks!
