Power Flow

Application Overview:

• See Power Flow Analysis Setup for details on user input options for this application.  

• For general details on running an application, selecting and displaying output variables, see Running DEW Applications.  

• The Available Output Variables for the application are described in the last section of this topic.

The Multi-phase Power Flow Application calculates voltages and currents for all user-selected circuits at the selected time point.

• If more than one time point is selected, the Power Flow results apply to the earliest time point selected.  

• If no time points are selected, Power Flow runs for the first time point.  

• Power Flow calculates voltages and currents for all phases present on every component in the circuit.

• Voltages are calculated as phase-to-return path for applicable sections of circuit, i.e. those with ground, neutral, or both.

• Voltages are calculated as phase-to-phase for delta connected sections, both two and three phase.  

• From the voltages and currents, a number of other variables of interest are determined.  

• Power Flow can be used to compare overloads and losses for multiple configurations of interconnected circuits, re-configured via switching operations.

Power Flow uses outputs from the Component Immittance and Load Estimation applications.  

• Power Flow will run the Component Immittance application if it has not run on the circuit for the type of month specified
  (Resistance calculations are a function of type of month due to monthly temperature variations).  

• Similarly, if Load Estimation has not run on the circuit for the specified time point, Power Flow will run Load Estimation.

Power Flow considers user-specified transformer and capacitor control modeling.  

• Controller input measurements may be specified anywhere in the circuit.  

• Voltage, power factor, power factor with voltage override, time, and temperature control can be implemented with switched capacitors,  

• Oscillating controllers can be detected and frozen automatically, based upon a user specified oscillation limit.  

• Controllers may be manually set and frozen by the user.

Application Run / Results:

See Running DEW Applications for general details on running the application, selecting and displaying output variables.

Power Flow may be set to run with constant current, constant power, or voltage dependent load models.
 

Constant Current:

• Constant current loads are calculated at given voltage from specified kW and kVAR loads.  

• The power flow calculation maintains the power factor of the original load.

• This model converges in fewer iterations (i.e. more rapidly) than the other two load models, giving results that are typically within few percent.

Constant Power:

• Constant power model fixes loads as constant real power (P, in kW) & reactive power (Q, in kVAR).

• Load current magnitude and angle at given voltage are adjusted to maintain constant real and reactive power.

• The constant power, i.e. real (P) & reactive (Q), load model may be used to model a defined system loading.

Voltage Dependent Loads:

The voltage dependent load model uses voltage dependency factors to provide a more detailed analysis of realistic field conditions, e.g. evaluating effects of voltage reduction on load.  A voltage dependency factor represents the percent change in load amps per percent change in load voltage.  

• A voltage dependency factor that applies to all loads of a circuit is specified in the Circuit (main properties) dialog.  

• A voltage dependency factor that applies to the load of an individual line or cable section is specified in the Load dialog, which is launched by the [Load] command button on the component's main properties dialog.  

• Both the voltage dependency factor specified at the circuit level and also the voltage dependency factor specified at the component level simultaneously modify loads.

• Power Flow adds the results from the two voltage dependency factor calculations together to obtain the overall voltage dependency factor.  

• Voltage dependency factors are ignored if the user does not select the Voltage Dependent Current load modeling option in Power Flow setup.

• If a voltage dependency factor is specified as positive, the load behaves like a constant impedance load, and load current increases with increases in voltage magnitude.  

• Increasing the voltage dependency factor corresponds to decreasing the load impedance magnitude.  

• If the voltage dependency factor is specified as negative, the load behaves like a constant power load and the load current decreases with increases in voltage magnitude.

• The voltage dependency factors can be adjusted in order to match field measurements.  

• The simplest approach to matching a field measurement is to adjust the circuit voltage dependency.

The Power Flow application flags a number of user-specified equipment and system operating limit violations.  

• Power Flow flags overloaded components by attaching a message to the components in violation.  

• The component messages indicate the type and percent of overloads encountered.

• Power Flow also flags system operation limit violations, with messages indicating the type and percent of violation.

• Only the worst operational limit violation for each circuit is flagged, e.g. only the lowest voltage is flagged in a circuit with multiple locations operating below the limit.

For details regarding any other specific component interactions related to this application, see component of interest in the Component Library.  

Available Output Variables:

For general details on running an application, selecting and displaying output variables, see Running DEW Applications.  The output variables available for display from the Load Estimation application are described in the following table.