Power quality & compensation
Harmonics, resonance, capacitor switching and PV DC side
This content now lives on its own page under the left menu; the card was removed from this page to avoid rendering the same result twice.
About Power quality hub
This page is the power-quality hub: it holds no study of its own and sends no engine request. Its six entries route to the pages that own the engine calls - harmonics (study.harmonics and the harmonic load flow, judged against the IEEE 519 and GB/T 14549-1993 limit tables and the IEC 61000 planning levels), resonance (resonance-scan: the full spectrum and the risky bands), voltvar (the volt-var optimisation, GB/T 12325-2008 and GB/T 14549-1993), filters (passive filter design under IEEE 519-2022 and GB/T 14549-1993 plus reactor selection), pv (PV and DC-side studies) and dc (the DC network per IEC 61660-1). The navigation status of this item is the aggregate of those six entries, so a single amber or red badge here means one of them still needs attention.
Power quality is judged as a package: a scheme can satisfy the voltage and loading limits and still be rejected because the distortion or the flicker exceeds the limit at the point of common coupling. Keeping every power-quality subject in one hub makes the verdict traceable - each number comes from the page that owns the study, and the hub badge tells you which of them is still open.
There is no calculation chain on this page: it links to six child pages, each of which runs its own engine study behind its own switch (harmonics, resonance-scan, volt-var optimisation, passive filter design, the PV study group, the DC network). The chain for each of them is described on its own page, always as input, then engine study, then the value read straight from the response. Linkage: the compensation, transformer and PV/DC equipment entered in the scheme are shared by all six, so a change made for one subject (a larger transformer, a capacitor step, a filter) shows up in the others - which is exactly why the hub exists.
| Parameter | What it means in the calculation |
|---|---|
| Max harmonic order | Highest order the spectrum is computed for: default 25, maximum 50. An explicit value switches the engine from the legacy 3/5/7/9/11 set to a full 2 to hMax sweep with the 1/h spectrum envelope extrapolated for the remaining orders. |
| Per-order harmonic current (%) | Harmonic current of each order as a percentage of the fundamental. The engine builds the spectrum from device type (VFD / EV charger / UPS / PV / nonlinear load) weighted by capacity, optionally vector-summed when the loads declare harmonic phase angles. |
| Comparison standard | Which limit table the per-order pass/fail follows. All four standards come back in one response, so switching between IEEE 519 / IEC 61000 / GB/T 14549 / ER G5/5 re-renders the limits locally without a new request. |
| Resonance scan band | The scan covers 50–2500 Hz (orders 1–50) with a coarse grid plus local refinement around each peak (scanPolicy=coarse+refine). Above 2.5 kHz the lumped-parameter network model no longer holds, so no out-of-band result is quoted. |
480 kWp PV on a 2500 kVA transformer with a 300 kvar capacitor bank: the engine locates a parallel resonance at h0 about 12.37 (about 618 Hz) with an impedance peak of 179.6 mohm against 3.5 mohm system impedance, i.e. an amplification factor of 4.15 at the busbar — which is why the 13th harmonic (650 Hz) sits only 4.3% away from the peak and must be checked against the GB/T 14549 limit instead of the IEEE 519 value.
IEEE 519-1992 Table 11.1 (voltage and current distortion limits), IEC 61000-2-2 / 61000-3-6 (LV and MV planning levels), GB/T 14549-1993 (harmonic limits for public supply networks, 0.38 kV band), EREC G5 Issue 5 (planning levels, 400 V), IEC 60287-1-1 / GB/T 50217 (cable capacitance feeding the resonance check) and IEC 60076-1 (transformer impedance).
- Why does the resonance matter if THDu is only 1.4%?
- Because THD averages over all orders while a parallel resonance amplifies one specific order. In the example the 11th and 13th harmonics see 3.4 to 3.7 times the system impedance, so a single order can exceed its own limit even when the total distortion looks comfortable — that is exactly what the near-resonance table flags.
- Does the capacitor bank always improve the network?
- No. Switching the planned bank in raises the bus voltage and the power factor and lowers the network loss, but it also creates a parallel resonance whose order h0 = sqrt(Ssc/Qc) falls as the kvar grows. That is why the engine reports the located h0 and the amplification factor next to the before/after numbers, and why a series reactor is recommended when h0 drifts close to a characteristic order.
- How long does the resonance scan take, and is it triggered automatically?
- It is lazy: nothing is computed until you press Run. The engine answers in a few milliseconds for the default plan (a coarse grid plus local refinement, well inside the 2.5 s time gate), reports whether the result was truncated (partial) or moved to the async task endpoint, and caches it by fingerprint — pressing Run again sends zero requests.
Every section is triggered on demand — this page sends no engine request when it opens (only the scheme-library read). All numbers are exactly what the engine returned; the planned capacitor bank is a what-if input and is never written back to the topology.