This simulator models a 10 MVA, 69 kV / 13.8 kV three-phase transformer, letting you compare standard vector-group connections, study independent phase loading on a three-unit bank, and see how the neutral connection (solid, resistive, or open/floating) affects behavior under balanced and unbalanced conditions.
• Operate tab: a real-time 3D model of the core, windings and cooling with Home view, Toggle casing (cutaway), Auto rotate and Expand camera controls, a clickable component list with a callout, colored arrows showing signed ideal phase flux at the current snapshot angle, live stats, an operating-history chart of neutral current, and a control desk to pause/advance simulated time (60 s steps or a 1-hour thermal-study jump), open/energize the primary, choose Connected load vs. Open circuit, toggle a leading (capacitive) load, select the vector-group design (Dyn11, Yyn0, Dd0, Yd1), toggle independent phase loads (three-unit bank), choose the load neutral (solid, resistive, open/floating), and view the energy pathway including neutral-conductor loss. • Circuit & measurements tab: a phase voltage/current/flux scope (solid normalized source voltages with dashed ideal flux waves lagging 90°, each phase a distinct color), a phase-current phasor chart showing each phase current plus their vector sum in white, an equivalent-circuit table with calculated values, and design & loss settings. • Experiments & diagnostics tab: a fault-injection menu (healthy circuit, Phase A load connection open, load neutral conductor open), a trip-logic toggle with protection thresholds and trip-reset, an event recorder with JSON export, a neutral comparison fixture that compares solid vs. open neutral behavior, a built-in calculation verification suite (Run verification suite), and guided investigation scenarios. • Learn & assess tab: lesson content on how three-phase transformer systems work, a knowledge-check quiz with reset, and a reference/model-scope note with a link to an external transformer-connection reference.
A three-phase transformer bank links three phase voltages that are 120° apart, and the way each side's windings are connected — Delta or Wye, with or without a grounded neutral, and at which relative clock-position — defines its vector group (Dyn11, Yyn0, Dd0, Yd1 here). The vector group determines the phase shift between HV and LV sides and, crucially, whether the connection provides a path for zero-sequence (neutral) current, which matters for unbalanced loads and ground faults.
With a solid neutral and unequal phase loads, current can flow back through the neutral conductor, keeping each phase's load voltage close to its intended value. With an open or floating neutral, that return path disappears — the model then forces the vector sum of the three phase currents toward zero even with unbalanced loading, which shifts the phase voltages at the load away from their nominal values instead. Selecting independent phase loads switches the underlying model to a three-unit grounded-wye bank, solved by complex nodal analysis with its own leakage impedance per unit, since a single balanced positive-sequence model can't represent genuinely unequal phase loading.
The phase voltage/current/flux scope shows each phase's source voltage as a solid curve with its ideal flux wave dashed and lagging 90° behind it — flux lags voltage because flux is the time-integral of voltage in an ideal inductive relationship. The phase-current phasor chart plots amber/cyan/violet phase currents together with their vector sum in white; in floating-neutral mode watch that white sum vector shrink toward zero even when the individual phase currents are unequal, which is the defining signature of an open neutral.
The neutral comparison fixture runs solid-neutral and open-neutral cases side by side under the same loading so the difference in phase voltages and neutral current is easy to see directly. The Run verification suite checks the model's internal invariants and limiting cases rather than a specific manufacturer's unit, and the bank model itself is an approximation: it does not claim to reproduce a three-limb core's true zero-sequence magnetic path, nonlinear saturation, harmonics, or earth faults, and the flux animation shows the ideal balanced source-voltage relationship rather than a field solution.
Balanced vector-group studies use an approximate positive-sequence equivalent circuit on a 10 MVA, 69 kV / 13.8 kV reference unit. When you select unequal loads, a non-solid neutral, or a load-open fault, the simulator switches to a three-unit grounded-wye bank model solved by complex nodal analysis, with independently prescribed leakage impedances and a stiff grounded source.
The load neutral selector lets you choose solid neutral, resistive neutral, or open/floating neutral. With a solid neutral, unbalanced phase currents can return through the neutral conductor; with an open/floating neutral, the vector sum of the phase currents is forced toward zero even under unequal loading, which changes the phase voltages seen at the load.
Enabling independent phase loads switches the model from a single balanced three-phase transformer to a three-unit grounded-wye bank, where each phase can carry its own leakage impedance and loading independently, letting you study unbalanced conditions that a simple balanced positive-sequence model cannot represent.
You can inject a Phase A load connection open fault or a load neutral conductor open fault. The neutral comparison fixture runs a side-by-side comparison of solid-neutral and open-neutral behavior so you can see directly how the neutral connection affects phase voltages and currents under the same loading.