GridEd · Module 2

Generator & Three-Phase AC

A B C (D/E/F added at 6 phases) Solid = voltage · dashed = current · the angle between them is the power factor
Frequency
60.0 Hz
Terminal voltage (RMS)
480 V
Shaft speed
1800 RPM
Power factor
1.00 —
Prime-mover effort
0 %

Spin the machine and connect a load. Then try disconnecting the prime mover and watch the frequency spin down.

f = (poles ÷ 2) × (RPM ÷ 60) = 60.0 Hz
Power factor = cos θ = 1.00  (θ = 0°)
Swing equation: 2H · dω/dt = Pmech − Pelec
Add load and Pelec jumps above Pmech, so the rotor slows and frequency dips until the governor raises the prime mover to catch up (primary frequency response). Disconnect the prime mover and Pmech=0 — the load drains the rotor's stored kinetic energy and it spins down, slower when inertia H is large. Only real power (the in-phase current) brakes the rotor, so a resistive load spins it down fast while a reactive load barely slows it. The reactive part still reshapes the voltage: inductive loads make it sag, capacitive loads prop it up (armature reaction).

Teaching notes

  • Power factor: with a load on, switch Resistive → Inductive. The current phasor swings behind the voltage; PF drops below 1 with no change in load size.
  • Supply follows demand: raise Load level — frequency dips, then the governor lifts prime-mover effort and frequency recovers. That's the whole grid's balancing act in miniature.
  • Inertia & blackout risk: set Inertia low, then Disconnect prime mover under load — frequency collapses fast. High inertia buys time. This is the crux of the renewables/low-inertia debate (Module 5).
  • Poles vs. phases: both are shown on the machine. More poles or higher RPM → higher frequency; number of phases sets how many evenly-spaced windings and waveforms.
1800 RPM
60
1.0×
3.0 s
40%
0°
Vₐ V_b V_c neutral current Wave height = voltage, spacing = frequency. Slow-motion so it's visible.
System frequency (real time) dashed = target · watch it dip under load and recover, or spin down when disconnected