Triplen harmonics, also known as the “third-order harmonics”, refer to harmonics that are multiples of the third harmonic. These include the 3rd, 9th, 15th, 21st harmonics, and so on. They have unique properties and effects when compared to other harmonics, especially in three-phase power systems:
- Zero Sequence: Triplen harmonics are of the zero-sequence type, which means they add algebraically in the neutral of a wye-connected transformer or load. This can lead to high neutral currents in a three-phase system, even if the phase currents are balanced.
- Causes: Equipment like computers, fluorescent lighting, and certain types of motor drives can produce significant triplen harmonics.
- Effects: Overheating in neutral conductors and transformers can occur due to high neutral currents caused by triplen harmonics. They can also lead to problems in power factor correction capacitors and can disrupt the operation of sensitive electronic equipment.
- Mitigation: To address triplen harmonic issues, delta-wye transformers can be used, which block zero-sequence currents. Additionally, larger neutral conductors, harmonic filters, or dedicated transformers can be deployed for loads known to produce significant triplen harmonics.
Note: Triplen harmonics are particularly problematic in four-wire, wye-connected systems since they can lead to high neutral currents. In three-wire systems, these harmonics are not problematic as there is no neutral for them to circulate in.