Glossary
The single alphabetical reference for the terms of art this manual uses: the power-systems vocabulary of the solver, the GB/regulatory vocabulary of the frequency and evidence work, and the GridSim-specific coinages. Each entry gives the definition at the level the code supports, the canonical value where the term carries one, and the grounding symbol or file.
Family tags: [PS] general power-systems usage; [GB] a GB grid, regulatory or NESO term; [GS] a GridSim-specific coinage, class name or in-code convention.
Canonical figures used throughout (a figure that reappears with a different value is a bug, not a variant):
| Figure | Value | Ground |
|---|---|---|
| case9 total real loss | ~ 4.641 MW | docs/benchmarking.md sec. 2a |
| case9 convergence | 4 iterations to 1.84e-14 pu | docs/benchmarking.md sec. 2a |
| WSCC inertia constants | H = 23.64 / 6.40 / 3.01 s | docs/benchmarking.md sec. 2c |
| WSCC total inertia | ~ 7.465 GVA.s | docs/benchmarking.md sec. 2c |
| gb-full size | 3,539 buses / 5,918 branches (raw 4,240) | docs/benchmarking.md sec. 2b |
| gb-spine size | ~316 buses (GSP level) | GDA NetworkModel/emit_spine_case.py |
| Residual worst mismatch | ~ 2e-7 MW | docs/benchmarking.md sec. 2a |
| RoCoF thresholds | legacy 0.125 Hz/s, modern 1.0 Hz/s | Core/Dynamics/FrequencyLimits.cs |
| LFDD stage 1 / working set-point | 48.8 Hz / 49.2 Hz | FrequencyLimits.cs, StabilityMetrics.cs |
| Horizon | 169 hours (7 days + 1 h) | Core/Diagnostics/ForwardInferenceGuard.cs:HorizonHours |
| Bridge clock-skew allowance | 15 minutes | Core/Net/GridBridgeClient.cs:ClockSkewToleranceMinutes |
| Solve tolerance / iteration cap | 1e-8 pu / 30 | Core/PowerFlow/PowerFlowOptions.cs |
| Test suite | 552 tests | dotnet test tests/GridSim.Tests |
A
Admittance [PS]. The reciprocal of impedance, Y = 1/Z (per-unit in
GridSim). A branch's series admittance is ys = 1/(R + jX); real part
conductance, imaginary part susceptance. See Y-bus and
02-data-model-and-per-unit.
ALoMCP [GB]. Accelerated Loss of Mains Change Programme - the GB programme that retuned distributed-generation loss-of-mains relays from the legacy 0.125 Hz/s RoCoF setting to 1.0 Hz/s by around 2022. GridSim carries both thresholds and the MECHANICAL tab shows margin against each. See RoCoF (dual threshold).
Assessment [GS]. A FrequencyAssessment (Core/Dynamics/FrequencyLimits.cs)
- the graded verdict on a frequency excursion: RoCoF, nadir, settle, per-limit breach flags and a worst-first summary string. See 05-frequency-dynamics.
Avoided cost [GS]. The pound figure the evidence engine attaches to a
counterfactual: recorded LFDD MW shed x Value of Lost Load x outage duration
(Core/Evidence/AvoidedCost.cs). Computed only when the record actually shed
load and the modelled device would have held the nadir above LFDD. The VoLL
default (£6,000/MWh) is a curated placeholder. See VoLL,
07-evidence-engine.
B
Backward-forward sweep (BFS) [PS]. The distribution-class solver
(Core/PowerFlow/BackwardForwardSweep.cs) for strictly radial feeders;
SolverSelector routes radial networks to it. Exact only at unity transformer
tap (tracked limitation). See 03-power-flow.
Bad data (identification) [PS]. The largest-normalized-residual loop: after
a converged fit that fails chi-square, the measurement with the largest normalised
residual is removed and the estimate re-run, pass by pass, with critical
measurements protected (Core/Estimation/BadDataAnalysis.cs). See Critical
measurement, Prior-backfill, 06-state-estimation.
Base MVA [PS]. The system-wide power base every per-unit conversion is
taken against (GridModel.BaseMva, 100 MVA for the WSCC and GB cases). See
Per-unit.
BiCGSTAB [PS]. ILU0-preconditioned biconjugate-gradient-stabilised Krylov
solver (Core/Numerics/Sparse.cs), the sparse Newton fallback when the direct
sparse LU reports singular. See 04-sparse-and-gpu-numerics.
BM - Balancing Mechanism [GB]. The near-real-time market through which
NESO accepts BIDs (turn down) and OFFERs (turn up). BM acceptances stream over
the bridge (BalancingActionDto with fuelType and synchronous); the RP1
tab grades each by its effect on intrinsic inertia.
Boundary [GB]. An ETYS transmission boundary - a defined cut across the GB
network (e.g. B6, Scotland-England) with a transfer limit. Modelled as
Boundary/BoundaryBranch in Core; carried by case boundaries.json, by the
bridge topology's boundaries block, and per-period by the estimated_state
lake's boundary_json. See 09-gda-integration.
Bus / bus type [PS]. A network node (Bus record, Core/Model/Model.cs)
classified Slack, Pv or Pq - the classification that decides which of a
bus's four electrical quantities are specified and which are solved. See
02-data-model-and-per-unit.
C
Chi-square (chi-square) consistency test [PS]. The global fit test on a converged
estimate: the objective J is compared against the chi-square 95 % threshold for the
fit's degrees of freedom (Core/Estimation/ChiSquare.cs). PASS means the
residuals are consistent with the declared sigmas; FAIL triggers bad-data
identification. NaN without redundancy. See
06-state-estimation.
Chi-square pill [GS]. The per-frame chi-square verdict shown on the WPF bridge
status bar when replaying source=estimated - driven by the state message's
estimate.chiPassed (src/GridSim.Wpf/MainWindow.xaml, bridge status pill;
BridgeProtocol.EstimateBlock). The honesty indicator a measurement-fitted
frame carries that a demand-scaled re-solve cannot.
Comp-range [GS]. The switchable reactive range (capacitive + inductive
MVAr) of a site's compensation plant, from the ETYS Appendix B table
(GDA NetworkModel/build_reactive_compensation.py). A switched MSC/reactor/
SVC's state is unobservable from settlement data, so a compensated bus's Q
pseudo-measurement carries the range as extra sigma (uniform-range standard
deviation, range/sqrt12), tagged pseudo-demand+comp-range
(build_estimator_measurements.py:_comp_range_by_bus). Declaring the real
uncertainty ended the systematic QInj rejections at compensated sites.
Convergence [PS]. Max mismatch below tolerance (default 1e-8 pu). The full Jacobian gives quadratic convergence: case9 in 4 iterations to 1.84e-14 pu.
Counterfactual [GS]. A "what the device would have done" result -
ProvenanceTag.Counterfactual. Never an input to another replay, and gated:
no counterfactual until the recorded baseline is reproduced with no device.
See Reproduced-baseline gate.
Critical measurement [PS]. A measurement that is the sole observer of some
state direction: its residual is structurally zero, its error undetectable,
and it is protected from bad-data removal (flagged critical in the export;
normalised residual NaN). se_residual_check.py --leverage arbitrates the
flags independently.
Crosswalk (BMU -> GSP) [GS]. The bounded table binding every Elexon BM unit
to its best GSP identity with an explicit method + confidence per row
(GDA NetworkModel/build_bmu_crosswalk.py ->
resolved/bmu_crosswalk.parquet). Ladder: name-match 0.9 (bmUnitName only) ->
strong TEC-register 0.75 (curated station codes + >=2-token matches) ->
OSUKED-nearest 0.7 -> weak TEC 0.75 -> interconnector 0.6 -> gsp-group-only
0.5 -> unmapped 0. See 09-gda-integration.
CSR - Compressed Sparse Row [PS]. The sparse-matrix storage of the large
solves (CsrMatrix, Core/Numerics/Sparse.cs); memory O(nnz). See
04-sparse-and-gpu-numerics.
CuratedPlaceholder [GS]. The ProvenanceTag for a figure standing in for
data not yet sourced, always accompanied by a [VERIFY] text marker. The tag
makes a number's provisional status travel with it; preserving these markers
is required. See [VERIFY] convention,
08-provenance-and-invariants.
D
Design basis (3,600 MW) [GS/GB]. The largest credible loss the stability
panels are measured against - Dogger Bank A+B+C
(NesoRp1Vm.DesignBasisLossMw), shown beside the superseded 1,800 MW
"secured event" convention.
Dispatch [PS]. Assignment of real-power output to generators.
Core/Dispatch/Dispatcher.cs applies default GB capacity factors by fuel and
balances the slack.
DNO [GB]. Distribution Network Operator (NGED, UKPN, NPg, SPEN, SSEN, ENWL). Their LTDS datasets are the raw material of the GDA case assembly. See LTDS, 09-gda-integration.
Dynamic MIF [GS]. The live intrinsic-energy floor a current credible loss
needs to hold a RoCoF limit: GVA.s = f0*deltaP/(2*RoCoF_limit)
(StabilityMetrics.DynamicMifGvaS). See MIF.
E
E - stored energy [PS]. Kinetic energy in a machine's rotating mass at
synchronous speed, E = H*MBase (MW.s). Summed over the fleet it is the
system inertia.
Era-mismatch [GS]. The documented reason the ETYS circuit overlay is
opt-in: ETYS 2025 describes today's network, so applying its real circuits
to a historical day injects reinforcements that did not exist then - the 2019
event day regressed from 46/46 chi-square-clean periods to 32/46 under the overlay.
Until the overlay is era-aware, the validated synthetic+curated spine is the
default (GDA NetworkModel/spine/build_spine.py:apply_etys_circuits). See
Spine overlay.
Estimated source [GS]. The bridge stream source source:"estimated": the
measurement-conditioned WLS lake (Derived/estimated_state) replayed frame by
frame, each frame carrying its own estimate quality block (J, chi-square verdict,
dof, removals). Contrast presolved (demand-scaled deterministic re-solve
lake) and live (static solve + per-period scalars). See
09-gda-integration.
ETYS [GB]. Electricity Ten Year Statement - NESO's published network and boundary data (boundaries + transfer limits; Appendix B circuit parameters). Grounds the boundary bars, the spine boundary limits and the opt-in circuit overlay.
Evidence dossier [GS]. The evidence verb's umbrella output, schema
gridsim-evidence/1: recorded vs simulated vs counterfactual columns, inertia
risk curve, fleet comparison and avoided cost, gated on a reproduced baseline.
See 07-evidence-engine,
10-file-and-wire-formats.
F
FFR - Fast Frequency Response [GB]. Sub-second active-power injection from converter-connected resources. In the swing model FFR is a separate power injection, never folded into stored energy E; across a staggered fleet it is non-additive. See Fleet dynamics.
Fleet dynamics [GS]. The result that a fleet of small units is not one big
device: intrinsic inertia is N-additive but staggered fast response is not, so
an equal-budget fleet reaches a deeper nadir (Core/Fleet/FleetDynamics.cs).
Fold map [GS]. fold_map.json - the gb-full-bus -> owning-spine-bus map
(plus spine-bus -> PES group) produced by the gb-spine fold's simultaneous BFS
and written to both case directories; resolves any bus to its PES group for
per-group demand scaling (GDA NetworkModel/emit_spine_case.py:_fold_map).
Forward-inference guard [GS]. The structural invariant that GridSim only
processes data at least 169 hours (7 days + 1 h) old:
ForwardInferenceGuard.HorizonHours = 169.0
(Core/Diagnostics/ForwardInferenceGuard.cs; widened from 25 h in July 2026).
Every dated input - event onsets, measurement takenUtc stamps, bridge state
ticks - passes through RejectFuture, which throws
ForwardInferenceException on anything newer. Enforced by construction, not
policy. See Horizon, 08-provenance-and-invariants.
Frame [GS]. A SimFrame(Model, Result, Hour, Tick, FrequencyHz, GenerationMw, DemandMw, ...) - the unit the UIs bind to. SimFrame.Model
carries post-solve tap ratios. Live simulation, presolved replay and the
bridge all produce frames.
G
gb-full [GS]. The materialised GB network - 3,539 buses / 5,918 branches,
assembled from normalised DNO LTDS tables plus the transmission spine
(GDA NetworkModel/assemble/run.py), reduced from a raw 4,240 buses by
busbar-section deduplication. Solves to a machine-epsilon residual; the sparse
estimation target.
gb-spine [GS]. The ~316-bus GSP-level reduction of gb-full
(emit_spine_case.py): one bus per NESO spine node, demand/generation folded
on by the BFS owner map, sub-GSP impedances dropped by design. The network
whose granularity matches the per-GSP measurement layer one-to-one - the
default estimation target. See Fold map.
GDA [GS]. Grid Data Archive - the read-only lake of GB grid data (DNO LTDS, Elexon settlement, NESO ETYS/TEC/inertia/frequency) GridSim's GB networks, measurements and estimated history are built from. Kept out of this repository. See 09-gda-integration.
Generator [PS]. The Generator record (Core/Model/Model.cs): Pg/Qg,
setpoint Vg, limits Qmin/Qmax/Pmax, machine base MBase, inertia
constant H (dynamics only - never enters the load flow).
gsp_ic_flows [GS]. Derived/gsp_ic_flows - per-period net interconnector
import at each landing GSP, from B1610 settlement volumes (ic_mw = 2 x sum signed MWh of the I_* units). Settlement-grade and era-deep (2019+); the
estimator's preferred interconnector source, with the operator-frames columns
as fallback. See 09-gda-integration.
GSP [GB]. Grid Supply Point - a transmission/distribution interface substation. The NESO anchor scheme's GSP names key the measurement layer, the crosswalk and the spine nodes.
GVA.s [PS]. Gigavolt-ampere-seconds - the unit of system inertia (total stored energy / 1000). The GB inertia risk curve sweeps 260/155/120/102/50 GVA.s.
H
H - inertia constant [PS]. Stored kinetic energy per MVA of machine
rating, in seconds (Generator.H). WSCC: 23.64 / 6.40 / 3.01 s.
Horizon [GS]. The 169-hour (7 days + 1 h) minimum lag every dated datum
must satisfy. Anything newer - recent or future - is rejected at ingestion
with a thrown ForwardInferenceException. The GDA side enforces the same
cutoff (Scripts/horizon.py; the bridge server masks every emitted tick and
rejects future starts/queries). The bridge client adds a 15-minute clock-skew
allowance when checking streamed ticks. See Forward-inference guard.
HVDC [PS]. High-voltage direct current - GB interconnectors and offshore links. Converter-connected (zero intrinsic inertia); corridor-correlated trips drive the credible loss.
I
ILU0 [PS]. Incomplete LU keeping the exact sparsity pattern
(Core/Numerics/Sparse.cs), the BiCGSTAB preconditioner.
Inertia (intrinsic vs market/contracted) [GS]. GridSim splits system
inertia into intrinsic (real synchronous rotating mass, GVA.s(i)) and
market/contracted (converter-provided response; may include real
synchronous condensers). Only intrinsic inertia enters the purchased-time
denominator. The bridge operator block streams the stratification
(synchronousInertiaGvaS, outturnInertiaGvaS, marketInertiaGvaS).
Interconnector [GB]. A cross-border HVDC link (IFA, IFA2, BritNed, Moyle, Nemo, NSL, ElecLink, Viking, Greenlink, EastWest). Its flow enters the estimator as a landing-GSP injection (see gsp_ic_flows) and its correlated-trip status the RP1 credible loss.
IWlsStep [GS]. The estimation-step seam
(Core/Estimation/WlsStep.cs:IWlsStep) - the estimator-side sibling of
ILinearSolver/IPowerFlowSolver. The estimator owns the loop (start point,
damping, convergence, chi-square, bad-data removal); the step backend owns
representation: how H is held, how the gain matrix is formed and solved, how
observability is gated, how residual covariance is computed. Implementations:
DenseWlsStep (<= threshold), SparseWlsStep (Gilbert-Peierls, structure
built once per pass), ConstrainedDenseWlsStep (Hachtel-style KKT); robust
reweighting drops in behind the same seam. See
06-state-estimation.
J
Jacobian [PS]. The matrix of partial derivatives of calculated injections
with respect to the voltage unknowns, in four polar blocks. Each Newton step
solves J*deltax = f. GridSim uses the full exact Jacobian. See
03-power-flow.
L
LFDD [GB]. Low-Frequency Demand Disconnection - automatic demand shedding
to arrest a falling frequency; GB stage 1 arms at 48.8 Hz
(FrequencyLimits.LfddFirstStageHz). An LFDD shed is a RecordedAction
(positive deltaP) and the substrate for avoided cost. Distinct from the 49.2 Hz
working set-point.
LNR - largest normalised residual [PS]. The bad-data identification
statistic: r/sqrtOmega with Omega the residual covariance diagonal. See Bad data.
LTDS [GB]. Long Term Development Statement - the DNO-published network dataset (nodes, circuits, transformers, demand, generation) that ingestion normalises into the per-licence tables the assembler consumes.
M
MATPOWER [PS]. The open power-system package whose .m case format and
published cases GridSim parses and validates against; case9's published
solution is the ground truth.
MBase [PS]. A machine's own MVA rating (Generator.MBase), the base its H
is quoted on.
Measurement set [GS]. A gridsim-measurements/1 document
(Core/Estimation/MeasurementSet.cs): case telemetry with per-measurement
kind, value, sigma and source, addressed by bus id / branch endpoints.
Horizon-checked on load when takenUtc is present. See
10-file-and-wire-formats.
MIF - Minimum Intrinsic Floor [GS/GB]. The intrinsic stored energy needed to hold a RoCoF limit for a given loss (720 GVA.s for 3,600 MW at 0.125 Hz/s). Computed live as the Dynamic MIF.
Mismatch [PS]. Per-bus difference between specified and calculated
injection, per-unit on BaseMva; convergence is max|f| < tolerance.
N
Nadir [PS]. The lowest frequency a fall reaches before response arrests
it (FrequencyAssessment.NadirHz).
NESO [GB]. National Energy System Operator - the GB system operator. Source of the limit ladder, ETYS, TEC, inertia outturn and frequency traces.
Newton-Raphson [PS]. The iterative power-flow method: linearise via the
Jacobian, solve J*deltax = f, step, repeat. Dense and sparse forms share the
same physics.
N-1 [PS]. The security standard requiring survival of any single-element
loss; nminus1/nminus1-sweep screen it.
O
Observability [PS]. Whether the measurement set determines the whole
state. The dense backend proves gain-matrix rank and names free directions;
the sparse backend runs an island sweep and reports rank = -1 (honest weaker
proof). Unobservable runs exit non-zero. See
06-state-estimation.
OLTC [PS]. On-load tap changer (Oltc record): regulates a controlled bus
voltage within a deadband; the SteadyStateSolver outer loop moves taps on
model clones and exposes the result via RegulatedModel.
P
Per-unit (pu) [PS]. Quantities as fractions of a base: power / BaseMva,
voltage / BaseKv, impedance x S_base/V_base^2. Actual kV = Vm x BaseKv.
PN fallback [GS]. The B-3 source ladder rung: when a settlement day has no
(or a partial, < 40-period) B1610 file, the per-GSP generation measurements
build from Physical Notification levels instead - submitted intent, not
metering - with looser sigmas (10 MW / 10 % vs B1610's 2 MW / 2 %),
provenance = "pn" end to end, and no group-demand sibling. Extends estimable
history to 2016-03 (GDA NetworkModel/build_gsp_measurements.py). See
09-gda-integration.
Prior-backfill [GS]. Observability restoration on bad-data removal
(--backfill-removals; EstimationOptions.BackfillRemovedFromPrior): a
removed real-power measurement is replaced by a pseudo evaluated at the start
state (the warm start / solved prior) with a deliberately looser sigma (3x,
floored at 5 % of value), tagged source = "removal-backfill-prior"
(WlsStateEstimator.BackfillSource) and itself never removable. Stops a
removal in a weakly-redundant region letting the state run away from the
prior. Reactive kinds are deliberately not backfilled. Off by default - it
changes what "removed" means (excluded -> replaced-by-prior).
Provenance tag [GS]. The six-value trust enum every evidence series
carries (Core/Diagnostics/Provenance.cs): Recorded,
DerivedFromRecorded, CuratedPlaceholder, Synthetic, Counterfactual,
Interpolated. Only Recorded is admissible as a real event input. See
08-provenance-and-invariants.
Pseudo-measurement [PS]. A prior dressed as a measurement with an honest,
loose sigma - the folded-demand injections (pseudo-demand, 25 %; group-
anchored 15 %), the reactive pseudos (pseudo-reactive), the voltage
schedule (pseudo-voltage-schedule, 1.01 +/- 0.03 pu). Tagged by source,
never presented as telemetry. See Virtual measurement.
Purchased time [GS]. Seconds from a credible loss to the 49.2 Hz working
set-point on the initial-RoCoF approximation, given intrinsic stored energy
(StabilityMetrics.PurchasedTimeSeconds). A physical duration: for a
3,600 MW loss, 720 GVA.s -> 6.4 s, 155 -> 1.4 s, 102 -> 0.9 s.
Q
Q-limit switching (PV->PQ) [PS]. The outer-loop model of a generator's excitation ceiling: a PV bus whose aggregate reactive output violates its limits is released to PQ with Q pinned at the binding limit, and the flow re-solves.
R
Recorded [GS]. The highest-trust provenance tag - a datum directly from an archived record; the only class admissible as a real event input.
Reproduced-baseline gate [GS]. No counterfactual until the recorded
event's RoCoF and nadir are reproduced with no device (RoCoF +/-15 %, nadir
+/-0.15 Hz -> Reproduced/Marginal/Failed; ReplayValidator, exit code 3 on
failure). See 07-evidence-engine.
Residual check [GS]. The independent NumPy instrument
(tools/crossval/residual_check.py) that rebuilds Y and evaluates
S = V ⊙ conj(Y*V)*baseMVA at every bus. Its estimation sibling is
se_residual_check.py (honesty / objective / optimality / leverage). See
11-validation.
RoCoF [PS]. Rate of change of frequency, df/dt = f0*deltaP/(2E) at the
instant of loss - a clean window onto inertia.
RoCoF (dual threshold) [GB]. GB carries two loss-of-mains relay settings:
legacy 0.125 Hz/s and modern (ALoMCP-retuned) 1.0 Hz/s
(FrequencyLimits). Every assessment reports breaches against both.
S
Settle [PS]. The frequency the system stabilises at after primary response
deploys (FrequencyAssessment.SettleHz).
Sigma (sigma) [PS]. A measurement's declared standard deviation, in its own
units; the WLS weight is 1/sigma^2. The GDA sigma models are documented per
product in 09-gda-integration; their calibration in
docs/benchmarking.md sec. 2f.
Slack bus [PS]. The reference bus: voltage magnitude and angle fixed, absorbing the system balance including losses. One per electrical island.
SolverSelector [GS]. The single source of truth for engine choice
(Core/PowerFlow/SolverSelector.cs): radial -> BFS; > 3,000 buses -> sparse
Newton; else dense Newton. CLI and GUI both route through it.
Sparse LU [PS]. Gilbert-Peierls-style sparse Gaussian elimination with
partial pivoting and RCM ordering (Core/Numerics/SparseLu.cs); null on a
singular matrix.
Spine [GS]. The GSP-level GB transmission backbone built by
GDA NetworkModel/spine/build_spine.py: one bus per deduplicated NESO GSP
site, synthetic Delaunay->Gabriel->prune+MST topology, curated corridor
overlay, boundary limits from NESO constraint files. gb-full's DNO fragments
attach to it; gb-spine is its estimation-grade reduction.
Spine overlay (SPINE_ETYS=1) [GS]. The opt-in replacement of the spine's
synthetic per-km impedances with the real ETYS Appendix B circuit list
(parallel-combined per site pair, provenance etys-appendix-b). Off by
default because of the era-mismatch caveat; enable it for investigations
of the present-day network only. See Era-mismatch.
Synthetic GB [GS]. The licence-free GB case (Core/Synthetic/SyntheticGb)
that lets the GB workflow run with no GDA lake present. Distinct from the
materialised gb-full.
System inertia [PS]. Total stored kinetic energy,
sum H*MBase / 1000 GVA.s (GridModel.SystemInertiaGvaS).
T
Tap ratio [PS]. A transformer's off-nominal turns ratio
(Branch.TapRatio, 1.0 nominal; a wire tap of 0 reads as 1.0).
TEC [GB]. Transmission Entry Capacity - the NESO register of contracted transmission-connected capacity; a crosswalk rung and a fleet-assembly source.
Tolerance [PS]. The convergence threshold on the mismatch
(PowerFlowOptions.Tolerance, default 1e-8 pu). The estimator's is
EstimationOptions.Tolerance (default 1e-8) on max |deltax|.
TSGB [GS]. Twin Scroll Grid Balancer - the device the frequency/evidence
apparatus models; TsgbSizer inverts the swing equation to size inertia and
FFR for target RoCoF and nadir.
V
[VERIFY] convention [GS]. The in-source marker that always accompanies a
CuratedPlaceholder figure. It describes the trust level of the software's
data and is preserved deliberately - stripping a [VERIFY] without sourcing
the figure defeats the integrity apparatus. See
08-provenance-and-invariants.
Virtual measurement [PS]. A structural zero-injection constraint at a pure
switching node, tagged virtual-zero-injection - soft (tight-ish sigma) under
WLS, promoted to a hard KKT equality under --method constrained
(ConstrainedDenseWlsStep.ConstraintSource).
VoLL [GB]. Value of Lost Load, £/MWh of unserved demand. Default £6,000/MWh, a curated placeholder (GB estimates span roughly £6k-£17k/MWh).
W
Warm start [PS]. Seeding a solve or estimate from a previous solution.
The assembler bakes a converged operating point into GDA cases; the estimator
accepts --warm-start (iterate from the case's solved point - standard EMS
practice, needed for real data) and --prior solve (solve the
measured-injection power flow first; its solution replaces the flat voltage
schedule as source = "prior-solved" and becomes the warm start -
Core/Estimation/MeasuredInjectionPrior.cs).
Working set-point (49.2 Hz) [GS/GB]. The operational floor purchased time
is measured to (StabilityMetrics.LfddWorkingSetpointHz) - deliberately
distinct from the 48.8 Hz LFDD relay arming point.
WSCC [PS]. The Western System Coordinating Council 9-bus system
(IeeeCases.Case9()), GridSim's physics ground truth.
Y
Y-bus [PS]. The nxn complex bus admittance matrix, Y*V = I. Extremely
sparse for real grids - the fact behind the CPU-first numerics
(04-sparse-and-gpu-numerics).
Reference tables
The GB frequency-limit ladder (Core/Dynamics/FrequencyLimits.cs;
StabilityMetrics.cs):
| Rung | Constant | Value |
|---|---|---|
| Nominal | NominalHz |
50.0 Hz |
| Operational | OperationalLow/HighHz |
49.8 / 50.2 Hz |
| Statutory | StatutoryLow/HighHz |
49.5 / 50.5 Hz |
| Working set-point | LfddWorkingSetpointHz |
49.2 Hz |
| LFDD stage 1 | LfddFirstStageHz |
48.8 Hz |
| RoCoF legacy | RocofLimitLegacyHzPerS |
0.125 Hz/s |
| RoCoF modern | RocofLimitModernHzPerS |
1.0 Hz/s |
The six provenance tags (Core/Diagnostics/Provenance.cs):
| Tag | Rule |
|---|---|
Recorded |
Only class admissible as a real event input |
DerivedFromRecorded |
Computed from records |
CuratedPlaceholder |
Unsourced stand-in; always carries [VERIFY] |
Synthetic |
Model-generated; never fed to the integrator as a record |
Counterfactual |
Device what-if; never an input to a replay |
Interpolated |
Gap-filled; usable for fidelity, never as an event source |
Protections & asset dynamics
| Term | Meaning |
|---|---|
| Asset dynamics | Authored per-asset behaviour (grid-following/forming inverters, passive plant) contributing a pAssetFleet swing term; ch. 5, 13 |
| Protection stage | Monitored quantity → threshold + dwell → action (TripInfeed/ShedDemand/OpenBranch); ch. 15 |
| LoM / RoCoF trip | Loss-of-Mains protection tripping embedded generation on rate-of-change-of-frequency (legacy 0.125, modern 1.0 Hz/s) |
| LFDD | Low-Frequency Demand Disconnection - a demand-shed protection arming at 48.8 Hz (modelled dynamically) |
| Recloser | A protection that opens a branch (topology) and auto-recloses after a delay |
| Island partition | The pre-pass that finds connected components over in-service branches and elects a per-island slack or blacks out a dead island (IslandPartition) |
| Reduction gate | The invariant that an absent/never-operating fleet leaves the frequency AND power-flow solve byte-identical |
See also
- 08-provenance-and-invariants.md - the provenance and horizon apparatus in depth
- 06-state-estimation.md - the estimation vocabulary in its mathematical setting
- 09-gda-integration.md - the GDA-side terms (crosswalk, fold, spine, lake products)
- 10-file-and-wire-formats.md - the schemas behind the format names used here
- ../manual/02-loading-networks.md - the case library the case-family terms refer to