This simulator models a balanced three-phase, 10 MVA, 69 kV / 13.8 kV substation transformer — the kind that steps transmission-level voltage down to a distribution bus. Switch vector-group connections, toggle automatic tap regulation, connect or open the secondary load, run factory-style tests, and inject faults while watching voltage, current and winding temperature respond.
• 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, live stat readouts, an operating-history chart of LV line voltage, 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 the automatic tap regulator, and view the energy pathway power balance. • Circuit & measurements tab: an HV/LV line-voltage phasor scope (separate HV and LV voltage bases, solid HV phases and dashed corresponding LV phases), a load & voltage-regulation sweep chart against the 13.8 kV / selected MVA base, an equivalent-circuit table with calculated values, and design & loss settings. • Experiments & diagnostics tab: a fault-injection menu (healthy unit, balanced secondary short circuit, HV supply sag to 80%, tap mechanism stuck at neutral, core-loss increase, cooling impairment), a trip-logic toggle with protection thresholds and trip-reset, an event recorder with JSON export, a virtual factory open-/short-circuit test runner, a built-in calculation verification suite (Run verification suite), and guided investigation scenarios. • Learn & assess tab: lesson content on how step-down transformation works, a knowledge-check quiz with reset, and a reference/model-scope note with links to external transformer-connection references.
A substation step-down transformer receives power at transmission or subtransmission voltage (69 kV here) and reduces it to distribution voltage (13.8 kV) so it can be safely delivered to feeders serving homes and businesses. The three-phase transformer's winding connection — Delta or Wye, with or without a grounded neutral — determines the phase-shift between HV and LV sides and how the unit handles unbalanced loads and ground faults; that's what the vector-group selector lets you compare.
Because distribution loads vary through the day, an automatic tap changer can adjust the effective turns ratio in discrete steps to keep secondary voltage within a target band despite HV-side sag or swell and changing load current. In this model, changing the vector-group selection preserves the nameplate line-to-line ratio by recalculating the internal coil turns ratio needed for that connection.
The HV/LV phasor scope plots each phase's HV voltage (solid) against its corresponding LV voltage (dashed) using separate per-side bases, so you can read relative phase shift introduced by the chosen vector group directly, independent of the magnitude difference between 69 kV and 13.8 kV. The load & voltage-regulation sweep shows how the 13.8 kV secondary sags as load admittance rises at the selected power factor — the automatic tap regulator, if enabled, counteracts part of that sag.
The equivalent-circuit table reports the calculated series impedances used to produce these curves, and the Run verification suite checks the model's internal power-balance and limiting-case invariants rather than validating a specific manufacturer's unit. Trip thresholds here are training values (primary current above roughly 6 pu, winding temperature above 120°C, or V/Hz above 1.2 pu for 1 second) and the model is a balanced positive-sequence approximation — it excludes zero-sequence networks, saturation, inrush and detailed OLTC mechanics.
It models a balanced three-phase, 10 MVA, 69 kV / 13.8 kV substation transformer using a balanced positive-sequence approximate equivalent circuit, with all main voltage readings as line-to-line RMS. It does not solve an unbalanced or earth-fault network, zero-sequence circuit, nonlinear saturation, inrush, or detailed on-load tap-changer switching.
The vector-group selector lets you choose between Dyn11, Yyn0, Dd0 and Yd1 winding connections. Changing the connection preserves the nameplate line-voltage ratio by changing the required coil turns ratio internally, letting you compare how different standard connections behave.
Enabling the automatic tap regulator lets the simulator adjust the transformer's tap position to help hold the secondary (13.8 kV) voltage steady as the HV supply or load conditions change, similar to an automatic on-load tap changer on a real substation transformer.
You can inject a balanced secondary short circuit, an HV supply sag to 80%, a tap mechanism stuck at neutral, a core-loss increase, or cooling impairment, then observe how trip logic (with thresholds like winding temperature above 120°C or V/Hz above 1.2 pu for 1 second) responds.