Definition
Triplen harmonics are the odd multiples of the third harmonic: the 3rd, 9th, 15th, 21st, and so on. They are a special concern in three-phase systems serving many single-phase nonlinear loads, because unlike most harmonics they do not cancel in the shared neutral conductor. Instead they arrive in phase across all three line conductors and add together in the neutral.
Why the neutral overheats
In a balanced three-phase system, the fundamental currents in the three phases sum to roughly zero in the neutral. Triplen harmonics break that cancellation: because they are in phase, the third-harmonic currents combine arithmetically, so the neutral can carry far more current than any single phase. Under heavily distorted load the neutral current can exceed the phase current, which is dangerous on installations where the neutral was sized assuming near-zero return current.
Relevance to mining power distribution
A facility powering many single-phase ASIC supplies off a three-phase panel is exactly the scenario where triplen harmonics accumulate. The practical response is to oversize the neutral conductor, treat it as a current-carrying conductor, and apply harmonic mitigation where distortion is severe. Transformers feeding the load may also need derating.
This is a specific case of the broader harmonics problem and a key reason power quality engineers worry about neutral sizing. See also power quality.
In Simple Terms
Triplen harmonics are the odd multiples of the third harmonic: the 3rd, 9th, 15th, 21st, and so on. They are a special concern in three-phase…