3-Phase Star-Star Auto Transformer with Tertiary

This component models a 3-phase auto transformer bank comprised of 3 single-phase banks and a tertiary winding. The tertiary winding may be configured as either delta or star configuration.

Options are provided so that the user may choose between either a magnetizing branch (linear core), or a current injection routine to model magnetizing characteristics. If desired, the magnetizing branch can be eliminated altogether, leaving the transformer in 'ideal' mode, where all that remains is a series leakage reactance.

Input Parameters

Transformer MVA	REAL	Constant	The apparent power rating of the transformer [MVA]

Base Operation Frequency	REAL	Constant	The base frequency of the electrical system, in which the transformer resides [Hz]

Leakage Reactance (H-L)	REAL	Constant	The leakage reactance between the high-side and the low-side windings. This can be calculated based on short-circuit test results [pu]

Leakage Reactance (H-T)	REAL	Constant	The leakage reactance between the high-side and the tertiary windings. This can be calculated based on short-circuit test results [pu]

Leakage Reactance (L-T)	REAL	Constant	The leakage reactance between the low-side and the tertiary windings. This can be calculated based on short-circuit test results [pu]

No Load Losses	REAL	Constant	The total no-load core losses of the transformer. Winding losses are not to be included in value [pu]

Ideal Transformer Model	Choice		Select Yes or No. This input must be Yes when modeling core saturation NOTE: 'Ideal' transformer should not be confused with an ideal ratio changer. 'Ideal' here simply means that the magnetizing branch has been eliminated (leakage reactance is still present as well)

Tertiary Winding	Choice		Select Star or Delta. This option determines the connection configuration of the tertiary windings only.

Delta Leading or Lagging			Select Lag or Lead. Select whether the delta-connected winding voltage will lead or lag the star-connected winding voltage. This input is enabled only if Tertiary Winding \| Delta is selected.

On-Load Tap Changer	Choice		Select Yes or No. Selecting Yes will enable the on-load tap changer, which requires an external signal input (see On-Load Tap Changer).

Winding Voltage (RMS)

REAL

Constant

The RMS voltage rating of the corresponding winding [kV]

NOTE: See Adjusting Saturation Properties for more details on these inputs

Saturation Enabled	Choice		Select Yes or No to enable or disable the core saturation routine NOTE: Always set the transformer to 'ideal' when enabling saturation. Otherwise, both the magnetizing branch and the saturation routine will both be used.

Air Core Reactance	REAL	Constant	Usually approximately twice the leakage reactance [pu]

Inrush Decay Time Constant	REAL	Constant	The decay time for the transformer inrush current [s]

Knee Voltage	REAL	Constant	The knee point voltage corresponding to the knee point of the saturation curve [pu]

Time to Release Flux Clipping	REAL	Constant	Time interval from start-up in which the model will 'clip' (limit) the calculated flux linkage values. This is simply a modeling 'trick' to prevent instability at start-up [s]

Magnetizing Current	REAL	Constant	The percentage of primary winding current that flows through the transformer magnetizing susceptance. This value can be calculated based on the open-circuit test results. The magnetizing susceptance is calculated based on this value [%]

Name for Winding Current	REAL	Output	Name for the specified winding current [kA]

Name for Magnetizing Current (pu)	REAL	Output	Name for the magnetizing current [pu]

Name for Flux Linkage (pu)	REAL	Output	Name for the calculated flux linkage [pu]


STAR Connected Tertiary	DELTA Connected Tertiary

3-Phase Star-Star Auto Transformer with Tertiary

Description

Input Parameters