Definitions and units

Sign convention

Generators and loads in an AC power system can behave like an inductor or a capacitor, which corresponds to two different sign conventions — one from the generator’s and one from the load’s perspective, defined by the direction of power flow. Like PyPSA, eDisGo uses both conventions depending on the component.

Generator sign convention

../_images/cosphi-sign-convention_generation.png — Fig. 12 Generator sign convention in detail

Time series for generators and storage units (Generator, Storage) use the generator sign convention.

Load sign convention

../_images/cosphi-sign-convention_load.png — Fig. 13 Load sign convention in detail

Time series for loads (Load) use the load sign convention.

Reactive power sign convention

Using the generator sign convention, a positive reactive power (Q) means capacitive behaviour and a negative Q means inductive behaviour.

Using the load sign convention this is reversed: a positive Q means inductive behaviour and a negative Q means capacitive behaviour.

See Reactive power for how reactive power is set from a fixed power factor.

Units

Table 1 List of variables and units
Variable	Symbol	Unit	Comment
Current	I	kA
Length	l	km
Active Power	P	MW
Reactive Power	Q	MVar
Apparent Power	S	MVA
Resistance	R	Ohm or Ohm/km	Ohm/km applies to lines
Reactance	X	Ohm or Ohm/km	Ohm/km applies to lines
Voltage	V	kV
Inductance	L	mH/km
Capacitance	C	µF/km
Costs		kEUR