This simulator models a three-phase rack PDU and branch panel feeding single-phase server power supplies. Adjust rack real power, push load onto one phase, tighten the branch breaker rating, change power factor or line voltage, and watch how a total kW figure that looks fine can still hide an overloaded branch.
• 01 Facility laboratory tab: a real-time 3D workbench of the rack PDU, three-phase branch panel, phase A/B/C server groups and a neutral current sensor, with Home view, Focus selected part, Show full enclosure / cutaway, Exploded view, Auto rotate, Expand and Hide/show labels camera controls, clickable numbered components with callouts, live stats, a "what is happening" sequence readout, switch-state tokens and a cell-readings table. Experiment controls include Pause/resume simulation, Advance 10 ms, Advance 1 s, a playback-speed selector (10× slow motion, real time, 10× faster, 1 minute per second), Enable facility / Stop experiment / Reset branch protection actions, and sliders for rack real power (3–40 kW), additional load fraction on phase A (0–60%), phase branch rating (16–63 A), load power factor (0.7–1) and three-phase line voltage (380–480 V). • 02 Curves & measurements tab: a torque/load operating-point chart, a speed-and-current history chart, the model equations (phase voltage, phase current, neutral current formula and the branch thermal-accumulator trip equation) and snapshot measurement readouts for phase A/B/C current, fundamental neutral current, served rack load and disconnected load. • 03 Experiments tab: guided experiment presets (balanced rack, phase A crowded, lower power factor, reset a persistent overload) plus a Model verification bench ("Run model checks") that checks the model with independent fresh instances, and a timestamped event log with a trial-report export. • 04 Learn & assess tab: lessons on three-phase distribution, balanced currents, unbalance and branch thermal trips, a two-question knowledge-check quiz with reset, and a scope-and-references note linking to external UPS/PDU documentation.
A three-phase rack PDU splits its incoming feed into three phase-to-neutral branches, each protected by its own breaker, and single-phase server power supplies are distributed across those branches. When the load is perfectly balanced across phases A, B and C at equal power factor, the three phase currents are equal and their vector sum — the fundamental neutral current — is close to zero.
Shifting load onto one phase (the imbalance control) raises that phase's current and its branch loading even though the rack's total kW figure hasn't changed, and it also raises the fundamental neutral current since the phasors no longer cancel. In this model, an illustrative I² thermal accumulator tracks each branch's exposure over its rating and latches the branch open once accumulated exposure reaches its threshold, which is why the same total kW can trip cleanly when balanced but overload a single branch when skewed.
The live stats readouts show phase A, B and C current, the fundamental neutral current, served rack load and any disconnected load — a nonzero disconnected-load figure means a branch has tripped on thermal accumulation. The model equations panel gives the phase voltage (line-to-line voltage divided by √3), phase current, the neutral-current vector-sum formula, and the trip-accumulator rate equation, so you can check the readouts against the underlying math.
The Run model checks button in the Experiments tab runs the built-in verification bench against independent fresh model instances without disturbing your current trial, confirming the implemented equations behave consistently. This is a sinusoidal, equal-power-factor teaching model: it excludes harmonic neutral current, real conductor voltage drop and manufacturer time-current breaker curves, and phase load fractions are constrained to stay nonnegative.
Total kW is the sum across all three phases. Shifting load onto phase A with the imbalance control raises that phase's current and thermal exposure independently of the total, so a rack that looks fine on aggregate kW can still overload one branch.
The fundamental neutral current is the vector sum of the three phase currents (IN² = IA²+IB²+IC²−IAIB−IBIC−ICIA). It approaches zero when phases are balanced and rises as load is shifted toward one phase. Triplen harmonic neutral currents are outside this model's scope.
Each branch has an illustrative I² thermal accumulator: dθ/dt = [(I/Irating)²−1]/20, and the branch trips once θ reaches 1. Resetting branch protection clears the accumulated thermal memory, but a persistent overload — such as 35 kW on 32 A branches — will trip again.
The Run model checks button in the Experiments tab runs a set of automated checks against independent, freshly created model instances, leaving your current trial untouched, to confirm the phase-current, neutral-current and thermal-accumulator equations behave correctly.