The following transformer models are available in DEW:
Fixed Tap Transformers
Regulating Transformers
Voltage Regulators
See General Dialog Details for information on common dialog fields and commands, as only the highlighted fields and commands unique to the transformer dialog are addressed in this topic.
The transformer properties dialog, shown below for a Transmission Transformer,
is generally common for the various types of transformers. Some
noted exceptions include that Operating
Status field is typical only for in-station type transformers and
that the Fixed Tap
transformer has no [Controller]
command button.
Overload Data - allows user quick access to include or ignore any overload data entered for the component via the [Overload Data] command dialog. The inclusion status can also be set from the dialog.
Compensator - A Load Drop Compensator is used to control the voltage at a remote point. The real and reactive voltage drops to be compensated at the rated compensator current must be specified in the Controller dialog.
Operating Status - when applicable, allows the user to select the most appropriate operating condition for the transformer. The standard conditions are described below:
The Operating Status drop-down list contains the following selections:
8.000 forced oil - Forced oil for a very long time
8.000 forced air - Forced air for a very long time
2.000 forced oil and air - Forced oil and air for a very short time
4.000 forced oil and air - Forced oil and air for a short time
6.000 forced oil and air - Forced oil and air for a long time
8.000 forced oil and air - Forced oil and air for a very long time
Nominal - neither forced oil nor forced air
Note: The available operating conditions and relative time characteristics may be customized in the database for specific user applications.
The [Controller] command button found on the main component property dialogs of Regulating Transformers and Voltage Regulators launches the By-Phase Transformer Controller dialog:
This dialog is used to specify:
Allowed to Move - when selected sets automatic control for all phases. (Control is manual when unselected).
Customer Voltage:
Base - defines Voltage magnitude set point
Bandwidth - defines Regulating bandwidth
Current Step:
Phase A/B/C - allows step current for the tap changer to be input for each phase individually.
No Reg - when selected, general automatic control selection is overridden, such that selected phases will only operate manually.
Load Drop Compensator:
Current Rating - specifies the current transformer primary side current rating in amps.
Real Drop - specifies the real voltage drop compensation by the transformer in volts.
Reactive Drop - specifies the reactive voltage drop compensation by the transformer in volts.
Blocked Step - specifies the step beyond which the transformer tap changer is not allowed to move. (The tap may be blocked on either a positive or negative step).
Gang Controlled - when selected, sets gang control for all phases from same tap, which is then defined by user in the Controlled Phase drop down list.
Voltage measurement location:
Pick Voltage Measurement - allows mouse pointer
selection of the circuit location where voltage is to be controlled. In
order for transformer control to affect voltage measurement, a component
downstream of the transformer must be selected. If
a transformer control is bidirectional, then either the Voltage
Measurement Location
should be defaulted to the transformer itself or a Load Drop Compensator
should be specified.
Voltage Measurement Location window - provides drop down list for specifying the circuit location where voltage is to be controlled within the range specified by the base and bandwidth settings. If the selection is made via the mouse pointer, then the window displays the selected location.
Note:
The default measurement location for installation of transformer is at
secondary side of the transformer. The measured
value of the customer level voltage is determined from the distribution
transformer turns ratio located close to the voltage measurement. If
a line/cable section is specified for the voltage measurement, then the
turns ratio of the distribution transformer attached to the line/cable
section is used. The Load Button on the Line or
Cable dialogs may be used to access the Distribution Transformer Turns
Ratio specification.
Controller Oscillations:
A controller oscillation occurs each time that a controller reverses the direction of control.
Controller oscillations are counted for each individual controller.
The maximum number of allowed controller oscillations is defined in the database.
The [Overload Data] command button opens a dialog to enter seasonal overload ratings for the transformer, which depend upon either the season being analyzed or the transformer operating status.
None - when selected, any seasonal overload data entries are ignored.
Winter - specifies the overload kVA rating for transformer during Winter season.
Summer - specifies the overload kVA rating for transformer during Summer season.
The [Tap and Connection] command button opens a dialog to specify the tap, whether step up or step down, and the winding connection for a transformer.
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Tap - |
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For Fixed Tap Transformers and Voltage Regulators, the Tap value is set at 1.000 |
For Regulating Transformers, Tap values (from 0.9-1.1) are selected
from the drop down window. |
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Aligned with Feeder:
Note:
Refer to transformer specification to determine if the alignment results
in step-up or step-down. |
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Connection - specifies the winding connection for the transformer. Note: In connecting transformers, primary or secondary windings that have no return path connection can only be connected into portions of the system that also have no return path where a return path represents either earth conductor, neutral conductors, or both. |
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Power Flow:
Unrecognized transformer configurations are treated as wye-wye by Power Flow where the common point is connected to return paths if available.
Power Flow attaches a message to the transformers with unrecognized winding configurations.
For transformers with a primary winding connection of Wye with no return path and a secondary winding connection of Wye with a return path, the connection of unbalanced loads on the secondary side is not modeled.
Such connections can cause extremely large magnetizing currents.
If an unbalanced load is connected to the secondary side of this configuration, it is treated as balanced and Power Flow attaches a message to the transformer.
With automatic control, Power Flow moves all phase taps on delta connected transformers in unison.
With manual control, the user can specify the tap settings.
If the number of oscillations for an individual controller exceeds a user specified maximum number of oscillations, then Power Flow freezes the controller so that convergence may be achieved.
In an individual controller's number of oscillations exceeds the specified maximum, Power Flow freezes the controller to allow convergence.
A message is attached to each controller that Power Flow freezes due to excessive oscillations.
