In a three-phase wye circuit, which harmonic currents are known to be additive in the neutral?

In a three-phase wye circuit, triplen harmonics are known to be additive in the neutral. Triplen harmonics are defined as the harmonics that are multiples of three, such as the 3rd, 9th, 15th, and so on.

These harmonics have a unique characteristic in a wye configuration: in each phase, the triplen harmonics add constructively in the neutral wire. This is because, for every phase in a balanced three-phase system, the phase currents can be expressed as sine waves. When you take these sine waves for triplen harmonics, the phase components will be in phase, leading to an increase in the current that flows through the neutral wire.

In contrast, even harmonics, such as the 2nd, 4th, 6th, etc., do not exhibit this behavior in a three-phase system because they cancel each other out due to their symmetry. Similarly, two-phase and odd harmonics behave differently, either not contributing constructively to neutral current or being canceled in the balanced conditions of a three-phase system. Hence, the specific nature of triplen harmonics makes them additive in the neutral point of a three-phase wye circuit.