GridEd · Module 4

Grid, Black Start & the Daily Cycle

light load heavy at limit substation Dots show power-flow direction & loading. Lines trip if overloaded. Click a plant, line, or load.
Frequency
— Hz
Generation
0 MW
Demand served
0 MW
Renewable share
0 %
State
BLACKOUT

The grid is dark. The black-start plants (★ Hydro and the Gas turbines) can start with no external power. Start one, energize outward through a substation, and pick up load in blocks.

Power balance: 2H·df/dt ∝ (Pgen − Pload) = 0 MW  ·  f = —
Net load = demand − (solar+wind) = 0 MW, carried by dispatchable plants
Meshed DC power flow: parallel paths split by impedance; a line trips at >103%, or >100% for 30 min
The network now has loops: two lines feed the Factory, and an east substation ties the Hospital and Airport to a local gas unit. Power splits across parallel paths by impedance, so unloading one path loads the other. If a line trips on overload, its flow reroutes — which can overload the next line and cascade. Solar and wind are must-take with no inertia; the dispatchable plants follow the net load.

Teaching notes

  • Cascading trips: overload a line (concentrate demand, or trip a parallel path) and watch it open, reroute, and possibly take the next line with it. Lines trip at >103% instantly, or after 30 sim-minutes above 100%.
  • Loops & redundancy: the second Substation–Factory line and the east substation ring give alternate paths — open one and power finds another route (until that one overloads).
  • Who can black-start: hydro and combustion turbines (both gas units) can self-start; the big Coal steam plant must be cranked from a live grid.
  • Daily cycle: the profile keeps the last three days (today bright, older faded, weather varies). Net load dips midday under solar and ramps into the evening — the duck curve.
Clock speed:
demand solar wind dispatchable (net load) last 3 days overlaid · today bright, prior days faded · line = now