Transformer

Transformers provide a means to change the voltage from one node to another in the distribution system. Similar to the different line objects, a transformer object requires a configuration object to specify the details of the implementation.

For technical details on transformer modeling, see Lines and Transformers Theory. A typical transform implementation is

object transformer {
    name xfrmr_709_775;
    phases "ABC";
    from node_709;
    to node_775;
    configuration xfrmr_config_400;
    }

Transformer Parameters

Properties

transformer objects are derived from link objects, so any parameters of the link object are available as well.

The I/O column indicates whether a property is user-settable input (I), simulation-computed output (O), or both (IO).

Table 1: transformer table 1

Property Name	Type	Unit	I/O	Description
configuration	object	N/A	I	transformer_configuration object that describes the specific transformer implementation.
climate	object	N/A	I	climate object that determines the outside ambient temperature around the transformer.
ambient_temperature	double	degC	IO	Output of the ambient temperature around the transformer. The default is 22.8 C.
top_oil_hot_spot_temperature	double	degC	IO	The hot spot temperature of the top-oil in the transformer. Default initial value is the ambient temperature.
winding_hot_spot_temperature	double	degC	IO	The hot spot temperature of the transformer windings. Default initial value is the ambient temperature.
percent_loss_of_life	double	N/A	O	The percent amount of transformer's operational life used. If no initial value is given then the transformer is considered brand new.
aging_constant	double	N/A	I	Experimental value used in determining the transformer insulation breaking point. The default is 15000 K.
use_thermal_model	bool	N/A	I	Flag used to enable use of the thermal/aging model. Default is FALSE.
transformer_replacement_count	double	N/A	IO	Counter of the number times the transformer has been replaced due to lifetime failure
aging_granularity	double	s	I	The maximum time step between transformer age and internal temperature updates. The default is 300 seconds.
phase_A_primary_flux_value	double	Wb	IO	Instantaneous magnetic flux in phase A on the primary side of the transformer during saturation calculations
phase_B_primary_flux_value	double	Wb	IO	Instantaneous magnetic flux in phase B on the primary side of the transformer during saturation calculations
phase_C_primary_flux_value	double	Wb	IO	Instantaneous magnetic flux in phase C on the primary side of the transformer during saturation calculations
phase_A_secondary_flux_value	double	Wb	IO	Instantaneous magnetic flux in phase A on the secondary side of the transformer during saturation calculations
phase_B_secondary_flux_value	double	Wb	IO	Instantaneous magnetic flux in phase B on the secondary side of the transformer during saturation calculations
phase_C_secondary_flux_value	double	Wb	IO	Instantaneous magnetic flux in phase C on the secondary side of the transformer during saturation calculations

Transformer Thermal/Aging Model

A newly added feature to transformers in 3.0 is a thermal/aging model. New parameters are placed within the transformer and and transformer_configuration in order to use this new feature. An implementation of the thermal model within transformer is

object transformer {
    name xfrmr_709_775;
    phases "ABC";
    from node_709;
    to node_775;
    configuration xfrmr_config_400;
        use_thermal_model TRUE;
        climate Seattle;
        aging_granularity 300;
        percent_loss_of_life 20;
    }

Transformer State of Development

Transformer is considered a highly developed and validated model in terms of powerflow solutions, however, models may be developed to include more advanced features in the future. Additionally, future work may include additional transformer configurations.

Transformer Configuration

The transformer_configuration object describes the details of a particular transformer implementation. It includes information like the power rating, connection type, and nominal voltage on each side. A typical delta-delta transformer configuration would be implemented as

object transformer_configuration {
    name xfrm_config_400;
    connect_type DELTA_DELTA;
    install_type PADMOUNT;
    power_rating 500;
    primary_voltage 4800;
    secondary_voltage 480;
    resistance 0.09;
    reactance 1.81;
    }

Transformer Configuration Parameters

Properties

transformer_configuration does not declare inherited parent classes.

The I/O column indicates whether a property is user-settable input (I), simulation-computed output (O), or both (IO).

Table 2: transformer table 2

Property Name	Type	Unit	I/O	Description
connect_type	enumeration	N/A	I	Describes the electrical connection between the high and low side of the transformer. These may be referenced by keyword or number 0 - UNKNOWN - An unknown transformer that will throw an error when used. 1 - WYE_WYE - A wye to wye connected transformer. 2 - DELTA_DELTA - A delta to delta connected transformer. 3 - DELTA_GWYE - A delta to grounded-wye connected transformer. 4 - SINGLE_PHASE - A single leg of a wye to wye connected transformer. 5 - SINGLE_PHASE_CENTER_TAPPED - A single-phase, center-tapped transformer or split-phase transformer. Used to connect three-phase distribution to triplex-distribution.
install_type	enumeration	N/A	I	Describes the type of transformer the object represents. Used for informational purposes only. Valid types may be referenced by keyword or number 0 - UNKNOWN - No information on the transformer physical type. 1 - POLETOP - A pole-mounted transformer. 2 - PADMOUNT - A pad, or ground level transformer. 3 - VAULT - An enclosed transformer "building," either underground or above ground.
coolant_type	enumeration	N/A	I	The type of coolant used in the transformer. Valid types may be referenced by keyword or number 0 - UNKNOWN - An unknown and unknown coolant type that will throw an error when used. 1 - MINERAL_OIL - A transformer immersed in mineral oil. 2 - DRY - A transformer with air as its coolant. This type is not handled yet.
cooling_type	enumeration	N/A	I	The type of cooling used in the transformer. Valid types may be referenced by keyword or number 0 - UNKNOWN - An unknown and unknown cooling type that will throw an error when used. 1 - OA - A liquid immersed self cooled transformer. 2 - FA - A forced air cooled liquid immersed transformer. 3 - NDFOA - A transformer with non-direction forced oil and air flow. 4 - NDFOw - A transformer with non-direction forced oil and water flow. 5 - DFOA - A transformer with direction forced oil and air flow. 6 - DFOw - A transformer with direction forced oil and water flow.
primary_voltage	double	V	I	Nominal voltage of the primary winding side of the transformer.
secondary_voltage	double	V	I	Nominal voltage of the secondary winding side of the transformer.
power_rating	double	kVA	I	Nominal power rating of the entire transformer.
powerA_rating	double	kVA	I	Nominal power rating of windings associated with phase A if wye-connected or AB if delta-connected.
powerB_rating	double	kVA	I	Nominal power rating of windings associated with phase B if wye-connected or BC if delta-connected.
powerC_rating	double	kVA	I	Nominal power rating of windings associated with phase C if wye-connected or CA if delta-connected.
resistance	double	pu*Ohm	I	De-referenced characteristic resistance of the transformer
reactance	double	pu*Ohm	I	De-referenced characteristic reactance of the transformer
impedance	complex	pu*Ohm	I	De-referenced characteristic impedance of the transformer. Note that resistance and reactance above directly write the real and complex portions of this parameter, so only resistance and reactance or just impedance need to be specified.
resistance1	double	pu*Ohm	I	Secondary series impedance (only used when you want to define each individual winding seperately), pu, real
reactance1	double	pu*Ohm	I	Secondary series impedance (only used when you want to define each individual winding seperately), pu, imag
impedance1	complex	pu*Ohm	I	De-referenced characteristic impedance of the transformer. Currently only used with center-tap transformers. Defaults to zero; not required for operation. Allows user to reflect impedance values on both the primary and secondary side of transformer (primary is specified by impedance, secondary by impedance1 and impedance2). Phase 1 equals phase 1 of split-phasing.
resistance2	double	pu*Ohm	I	Secondary series impedance (only used when you want to define each individual winding seperately), pu, real
reactance2	double	pu*Ohm	I	Secondary series impedance (only used when you want to define each individual winding seperately), pu, imag
impedance2	complex	pu*Ohm	I	De-referenced characteristic impedance of the transformer. Currently only used with center-tap transformers. Defaults to zero; not required for operation. Allows user to reflect impedance values on both the primary and secondary side of transformer (primary is specified by impedance, secondary by impedance1 and impedance2). Phase 2 equals phase 2 of split-phasing.
shunt_resistance	double	pu*Ohm	I	Shunt impedance on primary side, pu, real
shunt_reactance	double	pu*Ohm	I	Shunt impedance on primary side, pu, imag
shunt_impedance	complex	pu*Ohm	I	Some transformer models support a shunt impedance value to represent no load losses (only wye-wye and center-tap transformers use this value at this time).
core_coil_weight	double	lb	I	The weight of the transformer's core and coil assembly.
tank_fittings_weight	double	lb	I	The weight of the transformer's tank and fittings assembly.
oil_volume	double	gal	I	The amount of oil contained within the transformer.
rated_winding_time_constant	double	h	I	The winding's time constant.
rated_winding_hot_spot_rise	double	degC	I	The winding hot spot temperature rise over ambient at rated transformer load. Default is 80 degrees C.
rated_top_oil_rise	double	degC	I	The top oil temperature rise over ambient at rated transformer load.
no_load_loss	double	pu	I	The losses through the transformer when there is no load.
full_load_loss	double	pu	I	This is the losses of the transformer when at rated load.
reactance_resistance_ratio	double	N/A	I	The ratio the reactance to the resistance for both shunt and series impedances of the transformer. default is 10.
installed_insulation_life	double	h	I	The transformer's operational time span.
magnetization_location	enumeration	N/A	I	winding to place magnetization influence for in-rush calculations Valid values: NONE, PRIMARY, SECONDARY, BOTH.
inrush_saturation_enabled	bool	N/A	I	flag to include saturation effects during inrush calculations
L_A	double	pu	I	Air core inductance of transformer
phi_K	double	pu	I	Knee flux value where the air core inductance interstes the flux axis of the saturation curve
phi_M	double	pu	I	Peak magnetization flux at rated voltage of the saturation curve
I_M	double	pu	I	Peak magnetization current at rated voltage of the saturation curve
T_D	double	N/A	I	Inrush decay time constant for inrush current

Transformer Thermal/Aging Model

A new feature added to transformers in 3.0 is the thermal/aging model. New parameters are added to transformer_configuration for this new feature. This model only works with a SINGLE_PHASE_CENTER_TAPPED transformer. A typical implementation is

object transformer_configuration {
    name xfrm_config_400;
    connect_type SINGLE_PHASE_CENTER_TAPPED;
    install_type PADMOUNT;
    power_rating 500;
    primary_voltage 4800;
    secondary_voltage 480;
        full_load_loss 0.006;
        no_load_loss 0.003;
        reactance_resistance_ratio 10;
        core_coil_weight 50;
        tank_fittings_weight 60;
        oil_volume 5;
        rated_winding_hot_spot_rise 80;
        rated_top_oil_rise 30;
        rated_winding_time_constant 0.5;
        installed_insulation_life 175200;
        coolant_type MINERAL_OIL;
        cooling_type OA;
    }

Transformer Configuration State of Development

Transformer Configuration is considered a highly developed and validated model in terms of powerflow solutions, however, models may be developed to include more advanced features in the future, and additional models may be included as needed.