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.
External connections to this component are described as follows:
The following diagram shows a schematic of the connection:
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STAR Connected Tertiary |
DELTA Connected Tertiary |
This component also includes an on-load tap changing capability.
Under configuration:
there are three fields to enter leakage reactances.
Parameter for no load losses is not included.
Tertiary winding can be either star or delta, configured through a choice box.
If tertiary is delta, another choice for delta leading or lagging
More: |
Name for Identification |
Text |
Optional text parameter for identification of the component. |
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Transformer MVA |
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REAL |
Constant |
The apparent power rating of the transformer [MVA] |
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Base Operation Frequency |
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REAL |
Constant |
The base frequency of the electrical system, in which the transformer resides [Hz] |
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Leakage Reactance (H-L) |
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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] |
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Leakage Reactance (H-T) |
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REAL |
Constant |
The leakage reactance between the high-side and the tertiary windings. This can be calculated based on short-circuit test results [pu] |
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Leakage Reactance (L-T) |
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REAL |
Constant |
The leakage reactance between the low-side and the tertiary windings. This can be calculated based on short-circuit test results [pu] |
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No Load Losses |
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REAL |
Constant |
The total no-load core losses of the transformer. Winding losses are not to be included in value [pu] |
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Ideal Transformer Model |
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Choice |
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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) |
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Tertiary Winding |
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Choice |
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Select Star or Delta. This option determines the connection configuration of the tertiary windings only. |
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Delta Leading or Lagging |
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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. |
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On-Load Tap Changer |
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Choice |
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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 RatingsWinding Voltage Ratings
Winding Voltage (RMS) |
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REAL |
Constant |
The RMS voltage rating of the corresponding winding [kV] |
NOTE: See Adjusting Saturation Properties for more details on these inputs
Saturation Enabled |
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Choice |
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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. |
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Air Core Reactance |
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REAL |
Constant |
Usually approximately twice the leakage reactance [pu] |
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Inrush Decay Time Constant |
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REAL |
Constant |
The decay time for the transformer inrush current [s] |
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Knee Voltage |
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REAL |
Constant |
The knee point voltage corresponding to the knee point of the saturation curve [pu] |
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Time to Release Flux Clipping |
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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] |
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Magnetizing Current |
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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 [%] |
Monitoring of Currents and FluxMonitoring of Currents and Flux
Name for Winding Current |
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REAL |
Output |
Name for the specified winding current [kA] |
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Name for Magnetizing Current (pu) |
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REAL |
Output |
Name for the magnetizing current [pu] |
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Name for Flux Linkage (pu) |
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REAL |
Output |
Name for the calculated flux linkage [pu] |
