This simulator models a generator step-up (GSU) transformer as a balanced, positive-sequence RMS circuit — series resistance and leakage reactance, a shunt magnetizing/core-loss branch, winding connection ratios, and two thermal lags. Follow generator energy from the low-voltage windings, through the magnetic core, out through the high-voltage windings, and onto the transmission connection.
• A 3D cutaway of the generator, step-up transformer and transmission connection, with tank-cutaway, auto-rotate and expand controls, plus a component legend. • A choice of network fixture — balanced impedance load or infinite transmission bus — and vector group (YNd11, YNd1, YNyn0, Dd0), with an off-circuit HV tap that requires isolating all sources first. • Controls to run time, advance minutes, energize the generator, open/connect the output breaker, apply an HV three-phase short-circuit fault fixture, and reset a trip. • Charts for thermal response (hot spot and top-oil temperature), power transfer (MW/MVAr), the three-phase winding phasor diagram, and a power accounting breakdown of output versus losses. • Guided experiments, a 19-check model-verification bench, a diagnostic challenge on current vs. voltage ratios, and a knowledge-check quiz.
The model's base case is 200 MVA at 13.8/230 kV, 50 Hz. The turns ratio is set from a = VHV,line / VLV,line = (230/13.8) × (1 + HV tap%/100), adjusted for winding connection factors (√3 for wye, 1 for delta) to get NHV/NLV. Internally E = a·VLV, and terminal voltage is V = E − I·Z, so current flowing out is limited by the equivalent series impedance.
Because power is conserved (S = 3·Vphase·Iphase*), a transformer that steps voltage up by roughly 16.7× steps current down by about the same factor — this is why the generator side carries several thousand amperes while the transmission side carries only hundreds, with power, not current, staying comparable across the ratio (minus losses). The load slider sets impedance-load admittance at nominal voltage, so power drawn actually varies with voltage squared; in grid mode, the infinite bus fixes terminal voltage and power instead follows source magnitude, angle and impedance.
Total input power splits as Pinput = Poutput + copper loss + core loss, with copper loss equal to |I_pu|²·R_pu times the MVA base — so copper losses grow with the square of loading while core losses stay roughly constant. Thermal response uses two lags: an 1800-second oil time constant and a 300-second hot-spot time constant, with cooling conductance of 0.018 MW/K when healthy and 0.006 MW/K when the cooling system has failed.
The short-circuit fixture uses an ideal generator source and transformer impedance only. Protection is an illustrative envelope: current above 2 pu, or V/Hz above 1.2 pu sustained for 0.3 s, or a hot spot above 130°C removes both source fixtures. Vector-group phase displacement (e.g. YNd11's 30° shift) is applied to the phasor display, and changing the vector group or network mode creates a fresh operating fixture. These are teaching thresholds, not plant relay settings, and the model excludes saturation, inrush, harmonics, zero-sequence/grounding currents and switching transients.
This is the normal, expected behavior of a step-up transformer, not a sign of loss. Voltage and current scale inversely across the turns ratio to conserve power: stepping voltage up by roughly 16.7× (13.8 kV to 230 kV in this model) steps current down by about the same factor, so power delivered stays comparable on both sides aside from the relatively small copper and core losses.
The ratio is a = VHV,line / VLV,line = (230/13.8) × (1 + HV tap%/100) in this model's base case, adjusted by winding connection factors (√3 for a wye connection, 1 for delta) to get the physical turns ratio NHV/NLV. Internally, induced voltage E equals a times the LV voltage, and terminal voltage equals E minus the voltage drop across the series impedance, I·Z.
Total input power splits into useful output plus copper loss plus core loss. Copper loss is proportional to the square of per-unit current times winding resistance, so it grows sharply as loading increases. Core loss comes from the shunt magnetizing/core-loss branch and stays comparatively constant with load, since it depends mainly on applied voltage.
The simulator applies an illustrative protection scheme: current above 2 per-unit, or volts-per-hertz above 1.2 per-unit sustained for 0.3 seconds, or a winding hot-spot temperature above 130°C removes both the generator and grid source fixtures. The short-circuit fault fixture itself uses only an ideal generator source and the transformer's own impedance to compute fault current.