GridEd · Module 3

Synchronization & Paralleling

Incoming generator Live grid Synchroscope pointer at 12 o'clock + dark lamps = in phase. Then it's safe to close.
Slip (gen − grid)
+0.60 Hz
Voltage difference
+40 V
Phase angle
0 °
Status
NOT SAFE

The incoming generator isn't matched to the grid yet. Match its speed and voltage, wait for the synchroscope to reach 12 o'clock, then close the breaker.

Slip: fslip = fgen − fgrid = +0.60 Hz  (synchroscope turns at this rate)
ΔV = +40 V  ·  Δphase = 0°
Inrush at closing ∝ |Vgen − Vgrid| (phasor difference) = 0.00 pu
Close only when all three are near zero: same frequency (pointer stops), same voltage (equal wave heights, dark lamps), same phase (pointer at 12 o'clock). Close out of step and the machine is yanked violently into synchronism — a large inrush current and shaft-torque shock that trips breakers or damages equipment. (Phase sequence must match too, assumed correct here.)

Teaching notes

  • The one move to make live: with the two waves clearly drifting past each other, press Close breaker. You'll get a red inrush spike, a shake, and a protection trip. That single failure sells why synchronizing is disciplined.
  • Then do it right: adjust speed until the waves stop drifting (pointer stops), adjust excitation until the wave heights match (lamps go dark), and close as the pointer passes 12 o'clock. Clean lock.
  • Three conditions: frequency, voltage, and phase must all match (plus phase sequence). Real plants use auto-synchronizers to hit the window.
  • Bridge to Module 4: every unit that joins the grid — including during a black-start restoration — must be synchronized exactly like this.
60.60 Hz
Grid is fixed at 60.00 Hz. Match this to stop the drift.
520 V
Grid is 480 V. Match this so the lamps go dark.
Grid voltage Generator voltage Two voltages on one time axis. They slide past each other until the frequencies match, then lock when in phase.