Voltage stability · continuation power flow
Load / DG scaling factor λ is increased in adaptive steps and the existing load-flow solver is solved for real at every point: the P–V curve, the nose (critical) point, the Q–V curve and the per-bus voltage-stability margin and risk level come from the engine.
Pick a scheme first — then this column can calculate
This column runs the real engine on your project scheme, and there is none yet — that is why no calculation buttons are shown here (they are not broken). Start with any of the ways below; the fastest is the built-in example (one click, real parameters).
10 kV incoming (200 MVA short-circuit level) → 1250 kVA transformer (Dyn11) → LV main switchboard → busbar → 5 feeders plus a fire/emergency ATS branch. 1000 kW calculated load, cosφ 0.85, power-factor target 0.95.
Load the real example scheme and start calculating →The scheme and its parameters go straight into your browser; replace the data with your own at any time.
Calculator mode computes the few outputs that only depend on parameters you type in yourself. Anything that genuinely needs the whole system (full-network load flow, coupling with other devices) is shown as “needs a scheme” and no number is given.
Calculator mode is not available for this column yet — use one of the ways below.
Nothing is pre-filled and nothing is invented: leave a required field empty and the result area says “unavailable”.
In the studio, place devices, wire them and pick models — that becomes your project scheme (drawings / BOM / report can be exported).
Open the studio →Use the chat bubble bottom-right, or Contact us — we will set the example to your site parameters.
Note: every number comes from the engine. With no scheme, nothing is invented here.
Definitions, units and why the number matters for selection and quotation. Searchable, grouped by topic, collapsed by default.
Every ? mark on this page opens the same explanation in place — no page change.
7 term(s) shown of 7
Per-unit bus voltage in a load-flow result: the node voltage divided by its base voltage, so 1.00 pu is nominal.
Why it matters: It is the acceptance number of every voltage-drop check (commonly 0.95–1.05 pu). A node below the band means equipment malfunction and a grid-code breach, and the answer is a larger cable, a different transformer tap or a compensation device — a quotation change, not a note.
Point of common coupling (PCC): the interface in the network where the customer installation and the utility network are coupled, and therefore where the connection conditions apply.
Why it matters: It defines what the utility may complain about and what you must prove: voltage band, harmonic distortion, flicker and voltage-dip behaviour are all specified at the PCC, not at the equipment terminals. Studies or measurements made somewhere else do not demonstrate compliance.
Reactive compensation rating Qc: the output of the capacitor bank, sized as Qc = P × (tan φ1 − tan φ2) to move the installation from its present to its target power factor.
Why it matters: It is the item being quoted, and its usable output drops in a harmonic-rich network unless a detuned (reactor-protected) bank is used. The target power factor is a customer input, not a default — quoting a bank without stating the target pf is not a complete offer.
Maximum loadability factor λmax of the continuation power flow: the multiplier applied to all loads at the nose point of the PV curve, the point where the voltage collapses.
Why it matters: It is the loading margin of the design: λmax = 1.35 means the network only collapses at 135 % of today load. Planners require a minimum margin (the number differs between grid codes — state the criterion used), and it decides whether a line reinforcement or more reactive compensation has to be quoted.
Low-voltage ride-through: the duty (and the capability) of a generator or inverter to remain connected while the voltage at the PCC dips along a specified voltage-versus-time profile, instead of tripping off.
Why it matters: It is a grid-connection condition in most markets: a plant that cannot ride through the required curve cannot be connected or must be retrofitted. Confirm the required LVRT curve before sizing the inverters, because it decides the hardware class.
Per-unit value: a quantity expressed as a fraction of a chosen base value (1.00 pu = nominal voltage or rated power), the standard language of power-system studies.
Why it matters: It lets a 0.4 kV LV board and a 110 kV network be compared on one axis and one chart. Voltage 0.95–1.05 pu is the usual acceptance band, so any per-unit figure in a report can be read directly against the criterion.
Loading: the current (or power) carried by a branch expressed as a percentage of its rated capacity.
Why it matters: It is the acceptance number for cables and transformers. Above 100 % the element will trip or have to be derated, and the margin left at the design case is exactly what the customer is paying for — so it must be shown with the assumption (load factor, ambient temperature) that produced it.
Frequently asked questions
- What can this calculator do?
- Switch the continuation power flow on, choose whether λ scales the load only or the generation only (DG), and press Run: the engine solves the load flow for real at every λ step and returns the P–V nose curve with the critical point (λmax, the critical voltage vCrit and the weakest bus), the Q–V curve and the per-bus voltage-stability margin with a risk level. Typical uses: finding how much extra load the network accepts before the nose point, identifying the weak bus to reinforce, and comparing the load-only with the generation-only direction. If the base load flow fails or does not converge, every stability number is null and the engine reports the reason instead of a value.
- What is λmax and how is the margin read?
- λ scales the load — or the generation in DG mode — from the base case, and the margin reported is λmax × 100, with the critical point being the first infeasible step. The nose curve shows the P–V trajectory up to it, vCrit is the voltage at the critical point and the weakest bus is the bus that limits the transfer, i.e. the one to reinforce.
- Why does the switch matter so much?
- With the switch off the request carries no studyOptions.enableContinuationPowerFlow, so the response is byte-identical to a run without this study and no continuationFlow block is returned at all. With it on, the engine solves every λ step for real; then either a nose point is found or the engine reports why the study is not evaluable — no number is invented in between.