CHITEK mitigates UPS input harmonics, phase imbalance and reactive swing in data centres using AHF on the UPS feeder and SVG on the mechanical bus. Harmonic current raises transformer temperature and can circulate between parallel UPS units; imbalance loads the neutral. Both are measured in a single survey at the point of common coupling before sizing.
UPS rectifiers, single-phase IT loads and VFD-driven cooling all sit on the same feeder. Harmonic current raises transformer temperature, phase imbalance loads the neutral, and reactive swing from chillers drags power factor down at part load. CHITEK conditions the feeder upstream of the UPS and on the mechanical bus.
Reviewed by the CHITEK power quality engineering team · Last updated
Data centres usually separate the two buses: the UPS feeder is a harmonic problem, the mechanical bus is a reactive problem. They are measured and sized independently.
| Aspect | AHF (Active Harmonic Filter) | SVG (Static Var Generator) |
|---|---|---|
| What it does | Injects a compensating current that cancels the harmonic current drawn by non-linear loads. | Supplies or absorbs reactive power continuously to hold power factor and support voltage. |
| Primary target | Current distortion (THDi) and harmonic spectrum at the point of common coupling. | Power factor, voltage fluctuation and reactive demand across the load cycle. |
| Typical trigger | VFD banks, rectifiers, welding sets, induction furnaces, LED drivers, UPS rectifiers. | Low or swinging power factor, voltage sag and rise, weak or long feeders, EV load steps. |
| Behaviour at light load | Compensation scales with the measured harmonic current, so output falls as load falls. | Holds output as required to reach the target power factor even at near-zero active load. |
| Use in this sector | Harmonic correction on the UPS input feeder, where rectifier harmonics circulate between parallel units. | Reactive and voltage support on the chiller and CRAC bus, where VFD starting and part-load operation move power factor. |
Installing a filter downstream of the UPS output is usually unnecessary, because the UPS already conditions its own output.
HPC / Cloud Provider / Colocation
Reflective pollution from UPS rectifiers
>12%
THD
Phase imbalance from single-phase IT load
>15%
Unbalance
Reactive impact from VFD chillers/CRAC
PUE
Deterioration
Bank / Securities / Insurance
Sag sensitive trading infrastructure
< 3ms
Sag Tolerance
Transfer shock during genset test/outage
±15%
Voltage Step
Harmonic source from VFD compressors
>8%
THD
5G Base / IoT / Distributed Room
Unstable supply at remote/rural sites
>20%
Sag Depth
Overload risk at single-cabinet sites
>80%
Load Ratio
Phase imbalance from single-phase 5G/IoT
>10%
Unbalance
Each case below is written up the same way: what the site was, what the survey measured before anything was specified, what was installed, and what the acceptance test showed afterwards. Projects marked Typical Configuration are illustrative — sizing for those always starts from a site survey rather than from the table.
Colocation / IDC
Harmonic current 204.96 A → 19.18 A; distortion 26.94% → 3.12%
The TR1 feeder of an IDC hall, running between 200 A and 850 A with a displacement power factor of 0.975 before the retrofit. The existing filter cabinet was rebuilt rather than replaced.
TR1 feeder of an IDC hall, running current 200–850 A, displacement power factor 0.975 before retrofit. The existing filter cabinet was rebuilt around a new 500 A active filter. At 814.13 A load current (82% load factor) the measured harmonic current peaked at 204.96 A with 26.94% distortion.
Harmonic current 204.96 A → 19.18 A · Distortion 26.94% → 3.12%
Covers one feeder of the hall, not the whole site. The figures are taken at 814.13 A load current (82% load factor), which is the point the commissioning report used for acceptance.
At the feeder upstream of the UPS, or on the mechanical bus feeding chillers and CRAC units. Installing downstream of the UPS output is possible but usually unnecessary, because the UPS already conditions its own output.
Indirectly. Harmonic current causes extra loss in transformers and cables and can force a transformer to run hotter than designed, so removing that current reduces those losses. PUE depends on the whole mechanical and electrical design, so the effect has to be measured rather than assumed.
Yes. Single-phase IT loads spread unevenly across the phases create negative-sequence and zero-sequence current. Harmonics are a waveform problem, imbalance is a distribution problem, and both are normally measured in the same survey.
Yes, in smaller ratings. Remote and rural edge nodes often have worse supply quality than a core data centre, so the survey step matters more there, not less.
Every project on this page started with a measured survey. Send us your single-line diagram and load list and we will tell you what we would measure first.
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