An SVG (Static Var Generator) is the voltage-source-converter counterpart to the older thyristor-switched SVC, and it wins on three engineering numbers: sub-5 ms step response, continuous -1 to +1 per-unit reactive range, and a smaller physical footprint at the same Mvar rating [S7][S10].
Specifying one is less about brand and more about five measured axes — response time, reactive range, grid voltage class, harmonic coordination with an active harmonic filter, and the governing standard such as NB/T 10643-2021 for wind-farm duty or the IEC 61954 / IEEE 1031 family for transmission-class STATCOMs [S9][S1]. A wrong choice on the first or fourth axis costs the project the entire reactive margin, so a process engineer should treat those as non-negotiable gates before price is discussed.
Response Time and Step Response: The Hard Gate
Sub-5 ms full-step response is the figure every modern low-voltage SVG product datasheet quotes, and it is the metric that separates an SVG from a contactor-switched capacitor bank (typically 200 ms to 2 s) [S7]. For flicker loads such as arc furnaces, rolling mills, and stud welders, an SVG that misses the 5 ms gate will not suppress voltage flicker no matter how large its Mvar rating is [S5].
Two gotchas hide in datasheets. First, "response time" is usually the controller's detection-to-command delay; the full settling time including PLL lock and current-loop rise is normally 1–2 ms longer, so ask vendors for the IEEE 1453 / IEC 61000-4-15 flicker-compensation step-response trace, not a marketing number. Second, on weak grids (short-circuit ratio below 3) the SVG's effective response slows because the PLL widens its bandwidth — confirm the vendor has a weak-grid mode or specify one [S10]. For more on how this compares with an active harmonic filter on a step disturbance, the selection map between APF and SVG is a useful side reference.
Reactive Range: -1 to +1 Per-Unit, and Why the Sign Matters
Modern SVGs quote a -1 ~ +1 per-unit compensation range, meaning the same unit absorbs and generates reactive power symmetrically [S10]. That is a real engineering gain over TSC (Thyristor-Switched Capacitor) banks, which are purely capacitive and can only be switched in discrete steps, so they over- or under-compensate at light load [S7].
Symmetric range matters for three duty cases: solar and wind plants with leading power factor at no-load (the SVG must absorb vars to hold 1.0 p.f.), industrial sites with mixed inductive and capacitive loads (e.g. a factory with PF-corrected motors plus long cable capacitance), and dynamic loads that swing from motoring to regenerating (hoists, elevators, CRTM inverters). If your load is purely inductive and steady, an SVG is over-spec and a detuned capacitor bank plus reactor still wins on cost per kvar — the static var generator entry in the encyclopedia catalogues the duty boundaries. Background on the older SVC architecture is in the related [SVC reference page](https://new.abb.com/facts/static-var-compensation-(svc)) [S1].
Grid Voltage Class: 400 V vs 6/10 kV vs 35 kV+
Low-voltage SVGs (380–480 V) dominate the Chinese and European industrial market and are typically built in modular 50–100 kvar blocks that scale to ~600 kvar per cabinet [S6][S7]. Medium-voltage SVGs (6 kV, 10 kV, 35 kV) are the standard product for mining feeders, large steel mills, and wind-farm collector stations; here the topology is usually a cascaded H-bridge or a three-level NPC IGBT stack with a multi-pulse transformer [S9].
The 35 kV and above class is where the technology converges with STATCOMs — often the same hardware, marketed under different names. NB/T 10643-2021, the Chinese national standard for wind-farm SVGs, is one of the few standards that explicitly tests 35 kV-class equipment at the point of common coupling and includes low-voltage ride-through (LVRT) and harmonic emission profiles [S9]. For a buyer, the practical rule: at 400 V specify a modular SVG; at 6–10 kV specify a transformer-coupled multi-pulse SVG with at least 5-level output; above 35 kV you are really buying a STATCOM and should reference IEC 61954 / IEEE 1031 type-test reports. Voltage-class data for each product line normally appears in the static var generator catalog entry — verify before cross-referencing to any vendor datasheet.
Harmonic Coordination: SVG vs APF, and the Hybrid Stack
An SVG is not an active harmonic filter, although the same IGBT stack can do both jobs with a software change. A pure SVG prioritises reactive current and will let harmonic current pass through; a pure APF (Active Power Filter) prioritises harmonic current up to its 50th–63rd order and treats reactive as a secondary target [S5][S8].
Two spec axes decide the trade-off: harmonic orders covered (2nd to 25th for six-pulse diode rectifiers, 2nd to 50th for modern IGBT drives) and the per-phase compensation current. If the site has variable-frequency drives above 50% of the transformer rating, specify a hybrid compensator (APF + SVG in the same cabinet) — vendors such as YT Electric and Lafaelt publish this as "Hybrid VAR Compensator" with separate IGBT modules sharing the DC bus [S5][S8]. For a side-by-side spec axis view, the reactive compensation vs harmonic filter decision map is the most direct cross-reference. Below the 50% threshold, a standalone SVG with detuned reactor is normally more cost-effective than a full APF.
Duty Standards: NB/T 10643-2021, IEC 61954, and IEEE 1031
NB/T 10643-2021 — Technical requirements and test methods of static var generator for wind farm — is the most explicit SVG-specific standard, issued by China's National Energy Administration, and it covers performance tests (response time, reactive accuracy), LVRT, anti-islanding, and harmonic current emission limits for wind-farm SVGs [S9]. For transmission-class STATCOMs the relevant type-test standards are IEC 61954 (power electronics for HVDC and SVC) and IEEE 1031 (functional specification for thyristor-controlled SVCs, still referenced for SVG control loops).
A frequent buyer mistake is to specify a wind-farm-class SVG (tested to NB/T 10643-2021) for an industrial site, or vice-versa. The wind-farm standard includes LVRT and grid-fault ride-through clauses that drive up cost; an industrial-grade SVG tested only to IEC 62477-2 (power electronic converter safety) is enough for a captive plant and is 20–35% cheaper per kvar [S9]. Ask the vendor which standard the type-test certificate covers before comparing price. For transmission or substation applications, the [SVC reference page](https://new.abb.com/facts/static-var-compensation-(svc)) is the historical baseline [S1].
Selection Map: Which SVG Fits Which Duty
Four realistic options line up against four decision axes. A 400 V modular SVG (50–100 kvar modules, 5 ms response) is the right pick for commercial buildings, data-centre PDUs, and small factories with PF correction as the only goal. A 6/10 kV multi-pulse SVG with step-up transformer is the standard choice for mining feeders and large induction-motor drives where voltage class is fixed at medium voltage. A hybrid VAR compensator (APF + SVG in one cabinet) is the right pick when harmonic and reactive both exceed thresholds and floor space is tight. A 35 kV cascaded H-bridge STATCOM is the right pick for wind-farm and large solar-plant collector stations where LVRT and reactive reserve at the PCC matter most [S9][S10].
Do not pick a 400 V modular SVG for a 6 kV mining feeder (insulation class fails), do not pick an NB/T 10643-2021 wind-farm SVG for a simple motor plant (over-spec by 20–35% on cost), and do not pick a pure SVG (no APF function) for a site with >50% non-linear load. The shortlist logic in two lines: lock the voltage class, then lock the harmonic overlap; the brand shortlist falls out of those two gates. Track the 2026 updates to NB/T 10643 series and the next IEC 61954 amendment for the next signal on LVRT and weak-grid ride-through rules.
For component-level specifications, see function generator, and vacuum generator.