Interactive simulator of a grid-forming battery black-starting a dead grid section, with animated breakers, a step-by-step sequence tracker, an event log, oscilloscope traces, and a live transformer magnetization curve

BESS.engineer / visualsCTRL / GFM / BLACK START

Black Start from a GFM Battery

A grid-forming battery energizes a dead network from zero volts: soft transformer magnetization versus inrush, converter current limiting, and load blocks picked up one at a time.

dλ/dt = ω·v bus voltage delivered current demanded current core flux dead
t = 0.0 s
00 / standby 01 / energize 02 / island live 03 / load pickup 04 / complete
bus voltage0.00pu
frequency—
load served0.00pu
peak current0.00/ 1.5 pu
SLD-BS / island energization1 × GFM BESS · 4 load blocks
One-line diagram of the black start island GFM BESS PCS · GFM Q1 open MV XFMR 0.69 / 34.5 kV Q2 open 34.5 kV bus · dead section
FIG. BS-1 / one-line of the black-start islandclick a feeder breaker (or focus + enter) to pick up a block
CH 1 / bus voltagepu · 4 s window
Bus voltage trace
CH 2 / inverter currentpu · stiff-source demand vs delivered
Inverter current trace
CH 3 / transformer core fluxpu · knee at 1.15
Transformer flux trace
CH 4 / magnetization curveλ vs i · live point
Magnetization curve with live operating point
CTRL / parametersper-unit on PCS rating
2.0 s
0.15 pu
SOE / event loglatest first
NOTES / inrush and black startread with FIG. BS-1

01 / Core flux is the time-integral of voltage: λ(t) = ∫v·dt. The core remembers volt-seconds, not volts.

02 / Closing a breaker at a voltage zero drives flux toward 2 pu (the 1−cos ωt offset). Past the ≈1.15 pu knee the core saturates and, from a stiff source, magnetizing current jumps to 5–10× rated — the red demand spikes on CH 2.

03 / A GFM converter carries only 1.2–2 pu. Against real inrush it either rides its limiter (distorted voltage, protection stress) or trips. That is why black start uses a soft V/f ramp: raise the envelope slowly and flux never crosses the knee, so the inrush current is never demanded at all.

04 / Path breakers close on the dead network: Q1 (LV) and Q2 (MV) shut before any voltage exists, so their closures are transient-free. The ramp then magnetizes transformer, bus, and cables together. Transients only come from closing onto a live system — Q1 in instant mode, or the feeder breakers during pickup.

05 / Load pickup: every block adds a current step plus short motor inrush, and droop dips the island frequency. Blocks must fit inside the headroom between served load and the current limit — oversized blocks collapse the island (EXP-04).

06 / Waveforms are slowed (display ≈6 Hz, default 0.5× speed) so individual cycles are visible; readouts show the modeled 60 Hz island.

07 / Model limits: single-phase worst-case equivalent — no per-phase point-on-wave spread, no core remanence, no sympathetic inrush between transformers. Inrush decay is compressed along with the timebase, and frequency is droop-only (no secondary control), so a loaded island settles below 60.00 Hz by design.

Control visualization — run EXP-01…04, or set the parameters yourself and click breakers on the one-line. © BESS.engineer / visuals library