Transformer

Create Function

Transformers can be either created from the standard type library (create_transformer) or with custom values (create_transformer_from_parameters).

pandapower.create_transformer(net, hv_bus, lv_bus, std_type, name=None, tap_pos=nan, in_service=True, index=None, max_loading_percent=nan, parallel=1, df=1.0, tap_dependent_impedance=nan, vk_percent_characteristic=None, vkr_percent_characteristic=None, pt_percent=nan, oltc=nan, xn_ohm=nan, **kwargs)

Creates a two-winding transformer in table net[“trafo”]. The trafo parameters are defined through the standard type library.

INPUT:

net - The net within this transformer should be created

hv_bus (int) - The bus on the high-voltage side on which the transformer will be connected to

lv_bus (int) - The bus on the low-voltage side on which the transformer will be connected to

std_type - The used standard type from the standard type library

Zero sequence parameters (Added through std_type For Three phase load flow) :

vk0_percent - zero sequence relative short-circuit voltage

vkr0_percent - real part of zero sequence relative short-circuit voltage

mag0_percent - ratio between magnetizing and short circuit impedance (zero sequence)

z_mag0 / z0

mag0_rx - zero sequence magnetizing r/x ratio

si0_hv_partial - zero sequence short circuit impedance distribution in hv side

OPTIONAL:

name (string, None) - A custom name for this transformer

tap_pos (int, nan) - current tap position of the transformer. Defaults to the medium position (tap_neutral)

in_service (boolean, True) - True for in_service or False for out of service

index (int, None) - Force a specified ID if it is available. If None, the index one higher than the highest already existing index is selected.

max_loading_percent (float) - maximum current loading (only needed for OPF)

parallel (integer) - number of parallel transformers

df (float) - derating factor: maximal current of transformer in relation to nominal current of transformer (from 0 to 1)

tap_dependent_impedance (boolean) - True if transformer impedance must be adjusted dependent on the tap position of the trabnsformer. Requires the additional columns “vk_percent_characteristic” and “vkr_percent_characteristic” that reference the index of the characteristic from the table net.characteristic. A convenience function pandapower.control.create_trafo_characteristics can be used to create the SplineCharacteristic objects, add the relevant columns and set up the references to the characteristics. The function pandapower.control.trafo_characteristics_diagnostic can be used for sanity checks.

vk_percent_characteristic (int) - index of the characteristic from net.characteristic for the adjustment of the parameter “vk_percent” for the calculation of tap dependent impedance.

vkr_percent_characteristic (int) - index of the characteristic from net.characteristic for the adjustment of the parameter “vk_percent” for the calculation of tap dependent impedance.

xn_ohm (float) - impedance of the grounding reactor (Z_N) for shor tcircuit calculation

OUTPUT:

index (int) - The unique ID of the created transformer

EXAMPLE:

create_transformer(net, hv_bus = 0, lv_bus = 1, name = “trafo1”, std_type = “0.4 MVA 10/0.4 kV”)

pandapower.create_transformer_from_parameters(net, hv_bus, lv_bus, sn_mva, vn_hv_kv, vn_lv_kv, vkr_percent, vk_percent, pfe_kw, i0_percent, shift_degree=0, tap_side=None, tap_neutral=nan, tap_max=nan, tap_min=nan, tap_step_percent=nan, tap_step_degree=nan, tap_pos=nan, tap_phase_shifter=False, in_service=True, name=None, vector_group=None, index=None, max_loading_percent=nan, parallel=1, df=1.0, vk0_percent=nan, vkr0_percent=nan, mag0_percent=nan, mag0_rx=nan, si0_hv_partial=nan, pt_percent=nan, oltc=nan, tap_dependent_impedance=nan, vk_percent_characteristic=None, vkr_percent_characteristic=None, xn_ohm=nan, **kwargs)

Creates a two-winding transformer in table net[“trafo”]. The trafo parameters are defined through the standard type library.

INPUT:

net - The net within this transformer should be created

hv_bus (int) - The bus on the high-voltage side on which the transformer will be connected to

lv_bus (int) - The bus on the low-voltage side on which the transformer will be connected to

sn_mva (float) - rated apparent power

vn_hv_kv (float) - rated voltage on high voltage side

vn_lv_kv (float) - rated voltage on low voltage side

vkr_percent (float) - real part of relative short-circuit voltage

vk_percent (float) - relative short-circuit voltage

pfe_kw (float) - iron losses in kW

i0_percent (float) - open loop losses in percent of rated current

vector_group (String) - Vector group of the transformer

HV side is Uppercase letters and LV side is lower case

vk0_percent (float) - zero sequence relative short-circuit voltage

vkr0_percent - real part of zero sequence relative short-circuit voltage

mag0_percent - zero sequence magnetizing impedance/ vk0

mag0_rx - zero sequence magnitizing R/X ratio

si0_hv_partial - Distribution of zero sequence leakage impedances for HV side

OPTIONAL:

in_service (boolean) - True for in_service or False for out of service

parallel (integer) - number of parallel transformers

name (string) - A custom name for this transformer

shift_degree (float) - Angle shift over the transformer*

tap_side (string) - position of tap changer (“hv”, “lv”)

tap_pos (int, nan) - current tap position of the transformer. Defaults to the medium position (tap_neutral)

tap_neutral (int, nan) - tap position where the transformer ratio is equal to the ratio of the rated voltages

tap_max (int, nan) - maximal allowed tap position

tap_min (int, nan): minimal allowed tap position

tap_step_percent (float) - tap step size for voltage magnitude in percent

tap_step_degree (float) - tap step size for voltage angle in degree*

tap_phase_shifter (bool) - whether the transformer is an ideal phase shifter*

index (int, None) - Force a specified ID if it is available. If None, the index one higher than the highest already existing index is selected.

max_loading_percent (float) - maximum current loading (only needed for OPF)

df (float) - derating factor: maximal current of transformer in relation to nominal current of transformer (from 0 to 1)

tap_dependent_impedance (boolean) - True if transformer impedance must be adjusted dependent on the tap position of the trabnsformer. Requires the additional columns “vk_percent_characteristic” and “vkr_percent_characteristic” that reference the index of the characteristic from the table net.characteristic. A convenience function pandapower.control.create_trafo_characteristics can be used to create the SplineCharacteristic objects, add the relevant columns and set up the references to the characteristics. The function pandapower.control.trafo_characteristics_diagnostic can be used for sanity checks.

vk_percent_characteristic (int) - index of the characteristic from net.characteristic for the adjustment of the parameter “vk_percent” for the calculation of tap dependent impedance.

vkr_percent_characteristic (int) - index of the characteristic from net.characteristic for the adjustment of the parameter “vk_percent” for the calculation of tap dependent impedance.

pt_percent (float, nan) - (short circuit only)

oltc (bool, False) - (short circuit only)

xn_ohm (float) - impedance of the grounding reactor (Z_N) for shor tcircuit calculation

** only considered in loadflow if calculate_voltage_angles = True

OUTPUT:: index (int) - The unique ID of the created transformer
EXAMPLE:: create_transformer_from_parameters(net, hv_bus=0, lv_bus=1, name=”trafo1”, sn_mva=40, vn_hv_kv=110, vn_lv_kv=10, vk_percent=10, vkr_percent=0.3, pfe_kw=30, i0_percent=0.1, shift_degree=30)

Input Parameters

net.trafo

Parameter	Datatype	Value Range	Explanation
name	string		name of the transformer
std_type	string		transformer standard type name
hv_bus*	integer		high voltage bus index of the transformer
lv_bus*	integer		low voltage bus index of the transformer
sn_mva*	float	\(>\) 0	rated apparent power of the transformer [MVA]
vn_hv_kv*	float	\(>\) 0	rated voltage at high voltage bus [kV]
vn_lv_kv*	float	\(>\) 0	rated voltage at low voltage bus [kV]
vk_percent*	float	\(>\) 0	short circuit voltage [%]
vkr_percent*	float	\(\geq\) 0	real component of short circuit voltage [%]
pfe_kw*	float	\(\geq\) 0	iron losses [kW]
i0_percent*	float	\(\geq\) 0	open loop losses in [%]
vk0_percent***	float	\(\geq\) 0	zero sequence relative short-circuit voltage
vkr0_percent***	float	\(\geq\) 0	real part of zero sequence relative short-circuit voltage
mag0_percent***	float	\(\geq\) 0	z_mag0 / z0 ratio between magnetizing and short circuit impedance (zero sequence)
mag0_rx***	float		zero sequence magnetizing r/x ratio
si0_hv_partial***	float	\(\geq\) 0	zero sequence short circuit impedance distribution in hv side
vector_group***	String	‘Dyn’,’Yyn’,’Yzn’,’YNyn’	Vector Groups ( required for zero sequence model of transformer )
shift_degree*	float		transformer phase shift angle
tap_side	string	“hv”, “lv”	defines if tap changer is at the high- or low voltage side
tap_neutral	integer		rated tap position
tap_min	integer		minimum tap position
tap_max	integer		maximum tap position
tap_step_percent	float	\(>\) 0	tap step size for voltage magnitude [%]
tap_step_degree	float	\(\geq\) 0	tap step size for voltage angle
tap_pos	integer		current position of tap changer
tap_phase_shifter	bool		defines whether the transformer is an ideal phase shifter
parallel	int	\(>\) 0	number of parallel transformers
max_loading_percent**	float	\(>\) 0	Maximum loading of the transformer with respect to sn_mva and its corresponding current at 1.0 p.u.
df	float	1 \(\geq\) df \(>\) 0	derating factor: maximal current of transformer in relation to nominal current of transformer (from 0 to 1)
in_service*	boolean	True / False	specifies if the transformer is in service
oltc*	boolean	True / False	specifies if the transformer has an OLTC (short-circuit relevant)
power_station_unit*	boolean	True / False	specifies if the transformer is part of a power_station_unit (short-circuit relevant).

*necessary for executing a balanced power flow calculation
**optimal power flow parameter
***necessary for executing a three phase power flow / single phase short circuit

Note

The transformer loading constraint for the optimal power flow corresponds to the option trafo_loading=”current”:

Note

vkr_percent can be calculated as follow :

\begin{align*} vkr\_percent &= \frac{P\_cu}{S\_trafo} \cdot 100 \end{align*}

Where
P_cu is the power loss in the copper in kW
S_trafo is the rated apparent power of the transformer in kW

Electric Model

The equivalent circuit used for the transformer can be set in the power flow with the parameter “trafo_model”.

trafo_model=’t’:

sequence = 0:

trafo_model=’pi’:

Transformer Ratio

The magnitude of the transformer ratio is given as:

\begin{align*} n &= \frac{V_{ref, HV, transformer}}{V_{ref, LV, transformer}} \cdot \frac{V_{ref, LV bus}}{V_{ref, HV bus}} \end{align*}

The reference voltages of the high- and low voltage buses are taken from the net.bus table. The reference voltage of the transformer is taken directly from the transformer table:

\begin{align*} V_{ref, HV, transformer} &= vn\_hv\_kv \\ V_{ref, LV, transformer} &= vn\_lv\_kv \end{align*}

If the power flow is run with voltage_angles=True, the complex ratio is given as:

\begin{align*} \underline{n} &= n \cdot e^{j \cdot \theta \cdot \frac{\pi}{180}} \\ \theta &= shift\_degree \end{align*}

Otherwise, the ratio does not include a phase shift:

\begin{align*} \underline{n} &= n \end{align*}

Impedance Values

The short-circuit impedance is calculated as:

\begin{align*} z_k &= \frac{vk\_percent}{100} \cdot \frac{net.sn\_mva}{sn\_mva} \\ r_k &= \frac{vkr\_percent}{100} \cdot \frac{net.sn\_mva}{sn\_mva} \\ x_k &= \sqrt{z^2 - r^2} \\ \underline{z}_k &= r_k + j \cdot x_k \end{align*}

The magnetising admittance is calculated as:

\begin{align*} y_m &= \frac{i0\_percent}{100} \\ g_m &= \frac{pfe\_kw}{sn\_mva \cdot 1000} \cdot \frac{net.sn\_mva}{sn\_mva} \\ b_m &= \sqrt{y_m^2 - g_m^2} \\ \underline{y_m} &= g_m - j \cdot b_m \end{align*}

The values calculated in that way are relative to the rated values of the transformer. To transform them into the per unit system, they have to be converted to the rated values of the network:

\begin{align*} Z_{N} &= \frac{V_{N}^2}{S_{N}} \\ Z_{ref, trafo} &= \frac{vn\_lv\_kv^2 \cdot net.sn\_mva}{sn\_mva} \\ \underline{z} &= \underline{z}_k \cdot \frac{Z_{ref, trafo}}{Z_{N}} \\ \underline{y} &= \underline{y}_m \cdot \frac{Z_{N}}{Z_{ref, trafo}} \\ \end{align*}

Where the reference voltage \(V_{N}\) is the nominal voltage at the low voltage side of the transformer and the rated apparent power \(S_{N}\) is defined system wide in the net object (see Unit Systems and Conventions).

Tap Changer

Longitudinal regulator

A longitudinal regulator can be modeled by setting tap_phase_shifter to False and defining the tap changer voltage step with tap_step_percent.

The reference voltage is then multiplied with the tap factor:

\begin{align*} n_{tap} = 1 + (tap\_pos - tap\_neutral) \cdot \frac{tap\_st\_percent}{100} \end{align*}

On which side the reference voltage is adapted depends on the \(tap\_side\) variable:

	tap_side=”hv”	tap_side=”lv”
\(V_{n, HV, transformer}\)	\(vnh\_kv \cdot n_{tap}\)	\(vnh\_kv\)
\(V_{n, LV, transformer}\)	\(vnl\_kv\)	\(vnl\_kv \cdot n_{tap}\)

Note

The variables tap_min and tap_max are not considered in the power flow. The user is responsible to ensure that tap_min < tap_pos < tap_max!

Cross regulator

In addition to tap_step_percent a value for tap_step_degree can be defined to model an angle shift for each tap, resulting in a cross regulator that affects the magnitude as well as the angle of the transformer ratio.

Ideal phase shifter

If tap_phase_shifter is set to True, the tap changer is modeled as an ideal phase shifter, meaning that a constant angle shift is added with each tap step:

\begin{align*} \underline{n} &= n \cdot e^{j \cdot (\theta + \theta_{tp}) \cdot \frac{\pi}{180}} \\ \theta &= shift\_degree \end{align*}

The angle shift can be directly defined in tap_step_degree, in which case:

\begin{align*} \theta_{tp} = tap\_st\_degree \cdot (tap\_pos - tap\_neutral) \end{align*}

or it can be given as a constant voltage step in tap_step_percent, in which case the angle is calculated as:

\begin{align*} \theta_{tp} = 2 \cdot arcsin(\frac{1}{2} \cdot \frac{tap\_st\_percent}{100}) \cdot (tap\_pos - tap\_neutral) \end{align*}

If both values are given for an ideal phase shift transformer, the power flow will raise an error.

Result Parameters

net.res_trafo

Parameter	Datatype	Explanation
p_hv_mw	float	active power flow at the high voltage transformer bus [MW]
q_hv_mvar	float	reactive power flow at the high voltage transformer bus [MVar]
p_lv_mw	float	active power flow at the low voltage transformer bus [MW]
q_lv_mvar	float	reactive power flow at the low voltage transformer bus [MVar]
pl_mw	float	active power losses of the transformer [MW]
ql_mvar	float	reactive power consumption of the transformer [Mvar]
i_hv_ka	float	current at the high voltage side of the transformer [kA]
i_lv_ka	float	current at the low voltage side of the transformer [kA]
vm_hv_pu	float	voltage magnitude at the high voltage bus [pu]
vm_lv_pu	float	voltage magnitude at the low voltage bus [pu]
va_hv_degree	float	voltage angle at the high voltage bus [degrees]
va_lv_degree	float	voltage angle at the low voltage bus [degrees]
loading_percent	float	load utilization relative to rated power [%]

\begin{align*} p\_hv\_mw &= Re(\underline{v}_{hv} \cdot \underline{i}^*_{hv}) \\ q\_hv\_mvar &= Im(\underline{v}_{hv} \cdot \underline{i}^*_{hv}) \\ p\_lv\_mw &= Re(\underline{v}_{lv} \cdot \underline{i}^*_{lv}) \\ q\_lv\_mvar &= Im(\underline{v}_{lv} \cdot \underline{i}^*_{lv}) \\ pl\_mw &= p\_hv\_mw + p\_lv\_mw \\ ql\_mvar &= q\_hv\_mvar + q\_lv\_mvar \\ i\_hv\_ka &= i_{hv} \\ i\_lv\_ka &= i_{lv} \end{align*}

net.res_trafo_3ph

Parameter	Datatype	Explanation
p_a_hv_mw	float	active power flow at the high voltage transformer bus : Phase A [MW]
q_a_hv_mvar	float	reactive power flow at the high voltage transformer bus : Phase A [MVar]
p_b_hv_mw	float	active power flow at the high voltage transformer bus : Phase B [MW]
q_b_hv_mvar	float	reactive power flow at the high voltage transformer bus : Phase B [MVar]
p_c_hv_mw	float	active power flow at the high voltage transformer bus : Phase C [MW]
q_c_hv_mvar	float	reactive power flow at the high voltage transformer bus : Phase C [MVar]
p_a_lv_mw	float	active power flow at the low voltage transformer bus : Phase A [MW]
q_a_lv_mvar	float	reactive power flow at the low voltage transformer bus : Phase A [MVar]
p_b_lv_mw	float	active power flow at the low voltage transformer bus : Phase B [MW]
q_b_lv_mvar	float	reactive power flow at the low voltage transformer bus : Phase B [MVar]
p_c_lv_mw	float	active power flow at the low voltage transformer bus : Phase C [MW]
q_c_lv_mvar	float	reactive power flow at the low voltage transformer bus : Phase C [MVar]
pl_a_mw	float	active power losses of the transformer : Phase A [MW]
ql_a_mvar	float	reactive power consumption of the transformer : Phase A [Mvar]
pl_b_mw	float	active power losses of the transformer : Phase B [MW]
ql_b_mvar	float	reactive power consumption of the transformer : Phase B [Mvar]
pl_c_mw	float	active power losses of the transformer : Phase C [MW]
ql_c_mvar	float	reactive power consumption of the transformer : Phase C [Mvar]
i_a_hv_ka	float	current at the high voltage side of the transformer : Phase A [kA]
i_a_lv_ka	float	current at the low voltage side of the transformer : Phase A [kA]
i_b_hv_ka	float	current at the high voltage side of the transformer : Phase B [kA]
i_b_lv_ka	float	current at the low voltage side of the transformer : Phase B [kA]
i_c_hv_ka	float	current at the high voltage side of the transformer : Phase C [kA]
i_c_lv_ka	float	current at the low voltage side of the transformer : Phase C [kA]
loading_percent	float	load utilization relative to rated power [%]

\begin{align*} p\_hv\_mw_{phase} &= Re(\underline{v}_{hv_{phase}} \cdot \underline{i}^*_{hv_{phase}}) \\ q\_hv\_mvar_{phase} &= Im(\underline{v}_{hv_{phase}} \cdot \underline{i}^*_{hv_{phase}}) \\ p\_lv\_mw_{phase} &= Re(\underline{v}_{lv_{phase}} \cdot \underline{i}^*_{lv_{phase}}) \\ q\_lv\_mvar_{phase} &= Im(\underline{v}_{lv_{phase}} \cdot \underline{i}^*_{lv_{phase}}) \\ pl\_mw_{phase} &= p\_hv\_mw_{phase} + p\_lv\_mw_{phase} \\ ql\_mvar_{phase} &= q\_hv\_mvar_{phase} + q\_lv\_mvar_{phase} \\ i\_hv\_ka_{phase} &= i_{hv_{phase}} \\ i\_lv\_ka_{phase}&= i_{lv_{phase}} \end{align*}

The definition of the transformer loading depends on the trafo_loading parameter of the power flow.

For trafo_loading=”current”, the loading is calculated as:

\begin{align*} loading\_percent &= max(\frac{i_{hv} \cdot vn\_hv\_kv}{sn\_mva}, \frac{i_{lv} \cdot vn\_lv\_kv}{sn\_mva}) \cdot 100 \end{align*}

For trafo_loading=”power”, the loading is defined as:

\begin{align*} loading\_percent &= max( \frac{i_{hv} \cdot v_{hv}}{sn\_mva}, \frac{i_{lv} \cdot v_{lv}}{sn\_mva}) \cdot 100 \end{align*}

net.res_trafo_sc

The short-circuit (SC) results are put into net.res_trafo_sc with following definitions:

Parameter	Datatype	Explanation
ikss_hv_ka	float	magnitude of the initial SC current at HV transformer bus [kA]
ikss_hv_degree	float	degree of the initial SC current at HV transformer bus [degrees]
ikss_lv_ka	float	magnitude of the initial SC current at LV transformer bus [kA]
ikss_lv_degree	float	degree of the initial SC current at LV transformer bus [degrees]
p_hv_mw	float	active SC power flow at HV transformer bus [MW]
q_hv_mvar	float	reactive SC power flow at HV transformer bus [MVAr]
p_lv_mw	float	active SC power flow at LV transformer bus [MW]
q_lv_mvar	float	reactive SC power flow at LV transformer bus [MVAr]
vm_hv_pu	float	voltage magnitude at the high voltage (HV) bus [p.u.]
va_hv_degree	float	voltage angle at the high voltage (HV) bus [degrees]
vm_lv_pu	float	voltage magnitude at the low voltage (LV) bus [p.u.]
va_lv_degree	float	voltage angle at the low voltage (LV) bus [degrees]