Conventions

gpf uses these units, bases, and sign conventions in every device model. The other modeling pages assume these conventions.

Per-unit system

Network equations are solved in per unit on the system MVA base (the case SBASE). Quantities entered on other bases, such as winding-base transformer impedances or converter ratings in amperes, are converted onto the system base during case loading. Bus voltage magnitudes are expressed in per unit of the bus base voltage (BASKV).

Units in inputs and results

Power quantities in input records and in reported results are in MW and Mvar. Voltage magnitudes are reported in per unit. Voltage angles are entered in degrees, and rendered reports display degrees; the solution arrays of the Python API carry angles in radians. Impedance-related record fields carry the unit stated by their data code (for example the transformer CZ code); converted values are per unit on the system base.

Sign conventions

Generation is positive when power is injected into the bus: a machine with positive PG supplies active power. Consumption is positive for loads: a load with positive PL withdraws active power. Shunt reactive components are positive when capacitive, so a positive shunt susceptance injects reactive power. Branch flows are reported at each terminal and are positive when power flows from the bus into the branch. HVDC converter results are an exception: they are reported as injections into the AC bus, so a converter that withdraws power (for example a rectifier) reports a negative active power.

Bus power balance

At every in-service bus the injections sum to zero: generation, minus load, minus shunt consumption, minus the flows into connected branches and devices. The mismatch reported during a solve is the residual of this balance in per unit on the system base, and the convergence tolerance bounds its largest absolute value over all buses.

Solver settings in case files

A revision 34 file's NEWTON record supplies the solve defaults: TOLN (in MW/Mvar, converted to per unit on the system base) becomes the convergence tolerance and ITMXN the iteration limit. An explicit solve option overrides the file. The same file's THRSHZ sets the zero-impedance threshold, described under zero-impedance ties. The remaining solution-parameter records (ACCN, the GAUSS, ADJUST, and TYSL records) are preserved for round-trip and carry no solve effect.