This simulator focuses on the single most consequence-heavy moment in generator operation: paralleling onto a live bus. Match voltage, frequency, phase sequence and phase angle, watch the synchroscope sweep, then practice closing the breaker within the correct window — or see what happens when a close is attempted out of tolerance.
• A 3D synchronizing switchboard with rotor motion and selectable components, plus a stats panel of live electrical readings. • A synchroscope where 12 o'clock means in-phase and clockwise rotation means the incoming generator is running fast, alongside an ANSI 25 sync-check relay panel showing live permissives. • Operator controls to run or step time, arm an autosynchronizer, and manually close or open the breaker, plus an incoming phase-sequence selector (ABC matched vs. ACB reversed) and a phase-angle fixture for the open-circuit starting condition. • Instrument views: three-phase voltage waveforms (incoming generator vs. bus), the three-dark-lamp method, and a phase-slip recorder tracking wrapped angle over time. • Post-close load sharing controls showing how governor demand sets real power and excitation sets reactive power once paralleled to a stiff grid. • Diagnostic fault injection — reversed phase wiring, VT measurement loss, blocked dead-bus energization, breaker failing to close, or a slow breaker — with an optional ANSI 25 closing interlock that can be disabled for a deliberate out-of-phase closing experiment. • A verification suite, guided experiments, an event log with JSON export, and a closing-impact current estimate for any contact closure attempted outside tolerance.
Before a generator's breaker can safely close onto an already-energized bus, four conditions must be satisfied together: matching phase sequence, voltage magnitude within tolerance, frequency within tolerance, and phase angle within a closing window. Get any of these wrong and closing the breaker connects two out-of-step voltage sources, which can drive a large transient current and mechanical shock through the machine and its shaft.
The synchroscope and three-dark-lamp method are the classic manual indicators: the lamps bridge corresponding phases and approach darkness together only when sequence, voltage and frequency all agree, while the synchroscope pointer's rotation rate and direction show the remaining frequency and phase mismatch. An ANSI device 25 sync-check relay automates this by permitting a close command only when its angle, voltage and frequency windows are all satisfied — and this simulator's angle check specifically predicts the contact-touch angle using the configured breaker travel time, so the close command is issued early enough for the contacts to actually touch near zero phase difference.
If a breaker close is attempted outside the permitted window, the simulator estimates the resulting initial symmetrical RMS current as the voltage difference between the two sources divided by the combined R + jX″ (subtransient reactance) of the circuit. This captures the basic severity of an out-of-phase or unmatched close, but it excludes DC offset, point-on-wave effects, shaft torsional stress, magnetic saturation and detailed relay clearing times — so treat it as an order-of-magnitude teaching estimate, not a protection study.
The model assumes balanced sinusoidal sources, a stiff bus, a four-pole machine, first-order voltage and speed actuators, and delayed breaker contacts, with post-close real/reactive power ramping over about 2 seconds rather than solving full electromechanical swing transients. Dead-bus energization is deliberately blocked in this lab, since paralleling procedure and safety wiring depend on the bus already being live.
Phase sequence must match (both sources rotating A-B-C or both A-C-B), voltage magnitude must be within tolerance, frequency must be within tolerance, and the phase angle between the two sources must be within the permitted closing window at the instant the contacts touch.
Each lamp is connected across corresponding phases of the incoming generator and the bus. Lamp brightness reflects the voltage difference across it, so all three lamps dim together and approach darkness only when phase sequence, voltage and frequency all agree between the two sources — a clear visual confirmation before closing.
It monitors voltage difference, frequency difference and phase angle between two sources and only issues a permissive to close the breaker when all three are within configured limits. This simulator's angle check also accounts for breaker travel time, predicting the angle at contact touch rather than at the moment the close command is sent.
Closing while voltage, frequency or phase are mismatched connects two out-of-step sources, which can drive a large transient current and mechanical torque through the generator and its shaft. This simulator estimates that initial symmetrical RMS current as the voltage difference divided by the combined subtransient impedance, as a teaching approximation of closing severity.