Harmonics in Multi-Pulse Rectifier Transformer
Multi-pulse rectifier transformers have been used in various HVDC power supplies, including electrification systems, telecommunication base station UPS, electric power substation UPS, supercomputing or data centre UPS, and so forth [13, 14, 15].
-Pulse Rectifier Transformer
Conventional three-phase rectifiers cause harmonics pollution at input current side, and therefore bring some hazard to AC electric network and the other electronic equipment, as shown in Figure 2.14. A three phase rectifier transformer (6-pulse transformer) with Y connection at secondary side of transformer is shown in Figure 2.14(a), and waveforms of 6-pulse output voltage for three phase rectifier transformer with delta connection at the secondary side is shown in Figure 2.14(b).
The current in phase A can be expressed as below, where the existing harmonics are 5, 7, 11, 13, ... Waveforms of input voltage and current for the 6-pulse transformer are presented in Figure 2.15. This 6-pulse rectifier transformer can reduce the total harmonics distortion (THD) of the input current.
Figure 2.14 Three phase rectifier transformer (6-pulse transformer). (a) three phase transformer with Y connection at secondary side. (b) waveforms of 6-pulse output voltage for three phase rectifier transformer with delta connection at the secondary side
Figure 2.15 Waveforms of 6-pulse input voltage and current