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| Table 1: THDI levels with phase-shifting transformers | ||||
| Number of UPS units | Dominant harmonics | Phase shift | Redundant operation ½ Sn to Sn | Downgraded operation* Sn |
| 2 | 12k 6 1 | + 30° | < 10% | 30% |
| 3 | 18k 6 1 | 6 20° | 5% | 13% |
| 4 | 24k 6 1 | 6 15°, + 30° | < 3% | 12% |
| 5 | 30k 6 1 | 6 12°, 6 24° | < 3% | 9% |
| 6 | 36k 6 1 | 6 10°,6 20°,+ 30° | < 3% | 7% |
| Table 2: Compliance with industry standards | |||||
| Harmonic | %H1Limit of IEC 61 000-3-4 | Without filter | LC Filter | 12-Pulse | THM |
| H3 | 21.6% | – | – | – | – |
| H5 | 10.7% | 32% | 2.9% | 2.8% | 2.5% |
| H7 | 7.2% | 3.5% | 1.9% | 1.5% | 1.5% |
| H9 | 3.8% | – | – | 6 | – |
| H11 | 3.1% | 7% | 3.8% | 9.1% | 2% |
| H13 | 2.0% | 2.7% | 1.9% | 4.7% | 0.5% |
| H17 | 1.2% | 2.5% | 1.7% | 1% | 1.1% |
| H19 | 1.1% | 2.1% | 1.3% | 0.7% | 0.9% |
| HDI | 25% | 35% | 6% | 10% | 4% |
| *Downgraded operation = UPS unit failure or disconnected for maintenance. Non-compliant figures: | |||||