Line - Inputs

Lines represent AC transmission lines connecting two buses with impedance parameters. Below are all input attributes that you can set for line components.

WARNING

Lines can only use AC carriers. For DC transmission, use Link components instead.

Basic

Attribute	Data Type	Unit	Default	Required	Storage Type	Description
type	string	n/a	(empty)	No	static	Name of a predefined line standard type. If set, the line standard impedance parameters are automatically calculated from the line length and number of parallel lines, overriding any manually set values for x, r, and b. Leave empty to manually specify impedance parameters.
carrier	string	n/a	(empty)	No	static	Carrier type for the line. Must be "AC" (alternating current) as lines only support AC transmission.
active	boolean	n/a	True	No	static	Whether this line is active and should be included in network calculations. Set to False to temporarily disable the line without deleting it.

Capacity

Attribute	Data Type	Unit	Default	Required	Storage Type	Description
s_nom	float	MVA	0	Yes	static	The maximum apparent power capacity of the line in MVA. This sets the thermal limit for power flow through the line.
s_nom_mod	float	MVA	0	No	static	The unit size for capacity expansion. When extending the nominal apparent power (s_nom), it can only be increased in multiples of this module size.
s_nom_extendable	boolean	n/a	False	No	static	Switch to allow the nominal apparent power (s_nom) to be extended in optimization.
s_nom_min	float	MVA	0	No	static	If the nominal apparent power (s_nom) is extendable in optimization, set its minimum value.
s_nom_max	float	MVA	inf	No	static	If the nominal apparent power (s_nom) is extendable in optimization, set its maximum value (e.g. limited by technical potential or right-of-way constraints).
build_year	int	year	0	No	static	The year when the line can be built or commissioned. Essential for multi-year capacity expansion planning models, which determine optimal investment timing and line retirement schedules.
lifetime	float	years	inf	No	static	The operational lifetime of the line in years. Essential for multi-year capacity expansion planning models, which use this to determine when lines retire (build year + lifetime). Set to "inf" for lines that never retire.

Electrical

Attribute	Data Type	Unit	Default	Required	Storage Type	Description
x	float	Ohm	0	Yes	static	The series reactance of the line in Ohms. Must be non-zero for AC lines in power flow calculations. If the line has series inductance L in Henries, then x = 2πfL where f is the frequency in Hertz. The series impedance is z = r + jx. Ignored if line type is set.
r	float	Ohm	0	No	static	The series resistance of the line in Ohms. Must be non-zero for DC lines in power flow calculations. The series impedance is z = r + jx. Ignored if line type is set.
g	float	Siemens	0	No	static	The shunt conductance of the line in Siemens. The shunt admittance is y = g + jb, where b is the shunt susceptance.
b	float	Siemens	0	No	static	The shunt susceptance of the line in Siemens. If the line has shunt capacitance C in Farads, then b = 2πfC where f is the frequency in Hertz. The shunt admittance is y = g + jb. Ignored if line type is set.
length	float	km	0	No	static	The physical length of the line in kilometers. Required when line type is set to calculate impedance parameters automatically. Also used for calculating capital costs.
terrain_factor	float	per unit	1	No	static	Multiplier for capital cost to account for difficult terrain. Values greater than 1 increase the capital cost to reflect higher construction costs in challenging terrain (e.g., mountains, water crossings).
num_parallel	float	n/a	1	No	static	The number of parallel transmission circuits (can be fractional). When line type is set, this is used to calculate the total impedance (more parallel lines reduce effective impedance). If line type is empty, this value is ignored.
v_ang_min	float	Degrees	-inf	No	static	Minimum voltage angle difference across the line in degrees. This is a placeholder attribute and is not currently used by any functions.
v_ang_max	float	Degrees	inf	No	static	Maximum voltage angle difference across the line in degrees. This is a placeholder attribute and is not currently used by any functions.

Power Limits

Attribute	Data Type	Unit	Default	Required	Storage Type	Description
s_max_pu	float	per unit	1	No	static or timeseries	The maximum allowed absolute flow per unit of the nominal apparent power (s_nom). Can be set less than 1 to account for security margins (e.g., n-1 contingency), or can be time-varying to represent weather-dependent dynamic line rating for overhead lines.

Costs

Attribute	Data Type	Unit	Default	Required	Storage Type	Description
capital_cost	float	currency/MVA	0	No	static	The cost per MVA of adding new line capacity. Includes investment costs (spread over the planning period) and fixed operations & maintenance costs. Only relevant when s_nom_extendable is True.