What are Triplen Harmonics and where do they happen?

Triplen harmonics are the odd multiples of third harmonics.The triplen harmonics orders are 3,9,15,21,. The triplen harmonic frequency is 150Hz,450 Hz,,750Hz etc.

What are Harmonics?

Any non periodical waveform has sinusoidal component and integral multiples of the sinusoidal components. The integral multiples of the sinusoidal component or fundamental components are called harmonics. If the current exactly follow the same waveform as of the voltage, the current waveform has only fundamental current and no harmonics exist.

Read More : Harmonics in AC circuit
additive triplen harmonics

However, if the current waveform is non linear to the voltage waveform, the current waveform contains harmonics. The order of harmonics depends on the shape of the current waveform, If the current waveform is symmetrical about the x- axis it does not contain even harmonics and it contains odd harmonics.

The order of harmonics can be categories as even and odd harmonics. The even harmonic order is 2,4,,6, 8 etc. and odd harmonics order is 3,5,7,9,11 etc. The frequency of harmonics order is;
fn = n x f
fn = Harmonic frequency
n  = Harmonic Order
f   =  Fundamental frequency

If fundamental frequency is 50 Hz,the second order harmonic frequency is 2 x50 = 100 Hz.

Apart from categorizing harmonics in the even and odd order, one more category of the harmonic order is triplen harmonics.

What are Triplen Harmonics?

The odd multiples of third harmonics is triplen harmonics .The order of triplen harmonics orders are 3,9,15,21,.

Triplen Harmonic Sources

The single phase non linear loads like computer,printer or any single phase electronic equipment draws non linear current from the sinusoidal voltage source and generates substantial third order harmonics. 

Why Triplen Harmonics are Troublesome?

If the single phase non linear loads are connected to the three phase four wire system, the triplen harmonic current caused by non linear loads does not cancel out rather it gets added. If the triplen harmonic current in each phase of three phase four wire system is 1 ampere, the current in the neutral wire will be 3 amperes. Thus the current flowing in the neutral overheats the conductor. 

The third harmonics cause following adverse effect on power system.

• Overloading and overheating of neutral conductors (up 173% of phase current).
• Overheating of delta winding in distribution transformers.
• High earth to neutral voltages.
• Distortion of voltage waveform (including ‘flat topping’).
• Poor power factor.

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