Quora says: "Single-phase power supplies for equipment such as electronic ballasts and PCs are the most significant source of Triplen harmonics. "
Wikipedia says: "In a normal
alternating current power system, the current varies
sinusoidally at a specific frequency, usually 50 or 60
hertz. When a
linear electrical load is connected to the system, it draws a sinusoidal current at the same frequency as the voltage (though usually not in
phase with the voltage).
Current harmonics are caused by non-linear loads. When a non-linear load, such as a
rectifier is connected to the system, it draws a current that is not necessarily sinusoidal. The current waveform can become quite complex, depending on the type of load and its interaction with other components of the system. Regardless of how complex the current waveform becomes, as described through
Fourier series analysis, it is possible to deconstruct it into a series of simple sinusoids, which start at the power system
fundamental frequency and occur at integer multiples of the fundamental frequency.
Further examples of non-linear loads include common office equipment such as computers and printers, Fluorescent lighting, battery chargers and also
variable-speed drives.
In
power systems, harmonics are defined as positive integer multiples of the fundamental frequency. Thus, the third order harmonic is the third multiple of the fundamental frequency. This type of harmonics is generated in non-linear loads. Semiconductor devices like transistors, IGBTs, MOSFETS, diodes etc are all non-linear loads. Transformers on saturation can also generate harmonics. Electrical motors do not contribute to harmonics generation. Motors needs to reach saturation level to generate harmonics current which is a very very rare occurrence. So semiconductors are the major contributors to harmonics generation. Non-linear loads create disturbances in the fundamental harmonic, which produce all types of harmonics. However, in this section we focus on the 3rd order harmonic due to its certain special characteristics in the context of powers systems.
[1]
3rd Order Harmonic Addition
Power is supplied by a three phase system, where each phase is 120 degrees apart. This is done for two reasons: Firstly it is because generators/motors that use three phases are more efficient due to the constant torque the phases supply, and secondly, after power is supplied to a load, the three phases can theoretically be added onto a neutral wire and cancel each other out. This saves the utility from creating return wiring to the
power plant. However, if the three phases contain 3rd order harmonics, the currents will not fully add to zero. As seen in the figure, the 3rd harmonic will add constructively with the 3rd harmonics within the other phases. This leads to an oscillating current in the neutral wire, which can be dangerous since it is designed (i.e. small-size conductors) to carry minimal current.
[1] To avoid 3rd order harmonics adding together
delta connections are used, and the current is cycled around the connection instead of combining into the neutral of a
wye connection."
