CHITEK supplies AHF and SVG for traction substations, rail feeders and EV charging sites, where large single-phase and pulsed loads inject harmonics and negative-sequence current. Traction rectifiers and DC fast chargers also pull power factor down at peak. Ratings follow a survey of harmonic spectrum, unbalance and reactive profile at the supply point.
Traction rectifiers, 27.5 kV single-phase feeds and DC fast chargers are all large single-phase or pulsed loads. They inject harmonics and negative-sequence current into the supply and pull power factor down at the charging peak. CHITEK supplies AHF for the harmonic feeders and SVG for reactive support at the transformer.
Reviewed by the CHITEK power quality engineering team · Last updated
Traction and charging loads are pulsed and often single-phase, so unbalance and reactive step appear alongside distortion.
| 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 feeders dominated by traction rectifiers and charger rectification. | Reactive support at the transformer, where charging peaks and standby states each pull power factor in a different direction. |
Charging sites are mostly an SVG problem; AHF is added when charger harmonics also have to be held inside limits.
Traction / Station / Depot
Harmonic injection from 24-pulse rectifier
>15%
THD
Equipment bank imbalance
>10%
Unbalance
Energy feedback voltage rise
Voltage
Rise
Traction Substation / AT / Section
Negative sequence from V/V connection
>8%
Unbalance
Wideband harmonic from 4Q converter
>12%
THD
Voltage loss along long-distance AT feed
>10%
Drop
Highway / Urban Fast / Bus Depot
Power impact from DC fast charging
120kW+
Load Step
Harmonic stack from 12-pulse chargers
>15%
THD
Overload & imbalance at charging station
>90%
Load
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.
EV Charging
Power factor held at target in both standby and charging; payback inside two years
A charging site on two transformers, 2,500 kVA and 2,000 kVA. Measured at the LV incoming panel the site sat at 0.1–0.2 capacitive power factor, because chargers draw almost no active power on standby while their rectifiers continue to exchange reactive power.
Charging site on two transformers (2,500 kVA and 2,000 kVA). Measured at the LV incoming panel, the site ran at 0.1–0.2 capacitive power factor because chargers draw almost no active power on standby while their rectifiers still exchange reactive power — a conventional capacitor bank cannot follow that. One existing capacitor cabinet was stripped and reused to house the SVG modules.
Power factor 0.1–0.2 capacitive → target value held in standby and under load
The savings figure follows from the site's own tariff and load profile and is not transferable to another site. CT accuracy of 0.2 class or better is a prerequisite, not an option.
A single-phase traction load connected between two phases of a three-phase system produces negative-sequence current. That heats three-phase machines on the same network and can push unbalance past the grid limit.
Mostly SVG. The main issue at a charging site is reactive demand and power factor across the standby and charging states, plus the load step when several vehicles start together. AHF is added when charger harmonics also have to be held inside limits.
Yes. Energy fed back during braking raises voltage on the DC and AC side, and converters may trip on overvoltage. Handling it belongs to the traction power study rather than to a filter on its own.
For a charging site the payback is driven mainly by avoided power factor penalties. It depends on the local tariff and the site load profile, so the number comes from your tariff rather than from a product sheet.
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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