Power System Tools & Calculators

Free, browser-based calculators for power system engineering. Every tool on this page runs entirely on your device: nothing you type is uploaded, stored, or logged. Each one shows the governing equation in full, classifies the answer against the relevant industry guidance, and links to the standards and textbooks behind the numbers, so you can check the result rather than take it on faith.

These are the calculations that come up constantly in interconnection studies, protection reviews, and graduate coursework. They are built for screening and for teaching: fast enough to try ten scenarios in a minute, honest enough to tell you where the model stops being valid. For a signed study you still need EMT or full network simulation, and each tool says so.

The calculators

Short-Circuit Ratio Calculator Grid strength at a point of interconnection, from fault level or Thévenin impedance. Classifies the result against the weak / moderate / strong bands used in IBR interconnection screening, adds the post-contingency (N-1) case, and computes the ERCOT-style weighted SCR when several plants share one electrical neighborhood. SCRWSCRX/Rfault current Open the calculator → Symmetrical Components Calculator Fortescue decomposition of any unbalanced three-phase set into positive, negative, and zero sequence, with draggable phasor diagrams for both the phase quantities and the sequence sets. Reports the voltage unbalance factor against IEC 61000-2-2, EN 50160, and NEMA MG-1 limits, and includes fault presets so you can see each fault type’s signature. V₁ V₂ V₀VUFfault signaturesphasors Open the calculator → Two-Bus Load Flow & Voltage Stability The exact closed-form solution of a slack bus feeding one load through a series impedance, drawn as a live single-line diagram. Traces the PV nose curve and the QV reactive-margin curve as you move the load, and reports maximum loadability, critical voltage, and the distance to voltage collapse. power flowPV curveQV curveloadability Open the calculator → Inertia, RoCoF and Frequency Nadir The frequency response to the loss of the largest infeed, from system inertia, load damping and aggregate governor droop. Reports the initial rate of change of frequency, then integrates the swing equation to find the nadir depth and timing and whether the trajectory reaches the first under-frequency load shedding stage. inertiaRoCoFnadirUFLS Open the calculator → Cable Sizing Calculator Checks a proposed cable against the three constraints that actually decide the size: derated ampacity after ambient, grouping and soil corrections; voltage drop against the permitted limit; and short-circuit thermal withstand from the adiabatic equation. Reports which of the three is binding. Tabulated inputs come from your standard, not from the tool. ampacityderatingvoltage dropwithstand Open the calculator → SRF-PLL Tuning Calculator Design a synchronous reference frame PLL from a bandwidth or settling-time target and a damping ratio, or analyse the loop gains you already have. Reports kp, ki, natural frequency, phase margin, overshoot, settling time, and the frequency-ramp phase error, with a numerically integrated step response, an open-loop Bode plot, and a screening check of bandwidth against short-circuit ratio. PLLbandwidthdampingweak grid Open the calculator → Per-Unit Calculator Base impedance, base current, and base admittance from a three-phase MVA and line-to-line kV base, with conversion between ohms, per-unit, and percent. Applies the change-of-base relation to move a device impedance from its nameplate rating onto the system base, and propagates voltage bases across a radial chain of transformer zones. per-unitZ basechange of basetransformer zones Open the calculator → Transmission Line Parameter Calculator Series and shunt parameters of a fully transposed line straight from tower geometry: GMD, effective bundle GMR, inductance, capacitance, total Z and Y, characteristic impedance, and surge impedance loading. Solves the exact long-line hyperbolic ABCD constants, reports the nominal-π error, voltage regulation, and the Ferranti rise, and draws the tower cross-section to scale alongside the voltage profile that only goes flat at SIL. GMD & GMRbundlingSILABCDFerranti Open the calculator → Fault Current Calculator Short-circuit current for three-phase, single-line-to-ground, line-to-line and double-line-to-ground faults from the positive, negative and zero sequence impedances. Draws the sequence-network interconnection for the selected fault, compares the severity of all four fault types, and reports the X₀/X₁ and R₀/X₁ ratios behind the effectively grounded classification. short circuitSLGsequence networksgrounding Open the calculator → Transformer Connections & Vector Groups Vector group decoder for two-winding transformers. Pick the HV and LV connections and the clock number to get the phase displacement, the line voltage ratio against the true winding turns ratio with its √3 factor, the nameplate impedance converted onto your system base and split into R and X, and a live zero-sequence equivalent circuit that shows which side can source earth-fault current. Dyn11clock numberzero sequencechange of base Open the calculator →

How to use these tools

Every calculator follows the same layout, so once you have used one you know all of them. Inputs sit on the left and update the results as you type; there is no submit button. The headline number is paired with a coloured classification chip and a plain-English note explaining what that classification means and what an engineer would normally do about it. Below that sit the secondary quantities and the equation the tool actually evaluated, typeset properly so you can compare it against your reference.

Three buttons let you take the result with you. Copy link (top right) puts a URL on your clipboard that reopens the tool with your exact inputs, which is the quickest way to send a case to a colleague or paste one into study notes. Save PNG (top right) downloads a summary card suitable for a slide or a report appendix. Copy results, beside the equation, gives you a plain-text block of the inputs and outputs for an email or a spreadsheet.

Each tool page also carries a worked example, an explanation of the underlying theory, a section on how to read the classification bands, and references to the standards and textbooks the thresholds come from. If you are teaching, the shareable links make it easy to hand students a specific case to explore.

What these tools are, and are not

They are screening and teaching instruments. The models are exact for what they represent, but what they represent is deliberately small: a single interconnection point, a single unbalanced phasor set, a single line between two buses. That is enough to build intuition and to sanity-check a result you got somewhere else, and it is often enough for a first-pass feasibility answer.

They are not a substitute for a study. Real interconnection work needs a full network model, credible contingency sets, and, in weak-grid or high-IBR cases, electromagnetic transient simulation with vendor-specific inverter models. Treat a number from this page the way you would treat a hand calculation: useful, checkable, and never the final word.

More on the way

If there is a calculation you keep redoing by hand, tell me which one and it will go on the list.