Chapter 15 - Load Flow Analysis

ETAP
PowerStation 4.0
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

User Guide
Copyright  2001
Operation Technology, Inc.
All Rights Reserved
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Chapter 15
Load Flow Analysis
The PowerStation Load Flow Analysis program calculates the bus voltages, branch power factors,
currents, and power flows throughout the electrical system. The program allows for swing, voltage
regulated, and unregulated power sources with multiple utility and generator connections. It handles both
radial and loop systems. Different methods are provided for you to select from in order to achieve the
best calculation efficiency.
This chapter defines definitions and explains the usage of different tools you will need to run load flow
studies. Theoretical background for different load flow calculation methods is also provided.
The Load Flow Toolbar section explains how can you launch a load flow calculation, open and view an
output report, or select display options. The Load Flow Study Case Editor section explains how can you
create a new study case, what parameters are required to specify a study case, and how to set them. The
Display Options section explains what options are available for displaying some key system parameters
and the output results on the one-line diagram, and how to set them. The Load Flow Calculation Methods
section shows formulations of different load flow calculation methods. Comparisons on their rate of
convergence, improving convergence based on different system parameters and configurations, and some
tips on selecting an appropriate calculation method are also found in this section. The Required Data for
Calculations section describes what data is necessary to perform load flow calculations and where to enter
them. Finally, the Load Flow Study Output Report section illustrates and explains output reports and
their format.

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Toolbar

15.1 Load Flow Toolbar
The Load Flow Toolbar will appear on the screen when you are in the Load Flow Study mode.
Run Load Flow Studies
Update Cable Load Current
Load Flow Display Options
Alert View
Load Flow Report Manager
Halt Current Calculation
Get Online Data
Get Archived Data

Run Load Flow Studies
Select a study case from the Study Case Editor. Then click on the Run Load Flow Study icon to
perform a load flow study. A dialog box will appear to specify the output report name if the output file
name is set to Prompt. The study results will then appear on the one-line diagram and in the output
report.

Update Cable Load Current
Selecting the Update Cable Load Current icon will transfer cable load current data from the previously
run load flow study. The data is transferred to the Operating Load Current in the Cable Editor for each
cable associated with the load flow study.

Load Flow Display Options
The results from load flow studies are displayed on the one-line diagram. To edit how these results look,
click on the Load Flow Display Options icon. For more information see Load Flow Display Options.

Alert View
After performing a load flow study, you can click on this button to open the Alert View, which lists all
equipment with critical and marginal violations based on the settings in the study case.

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Toolbar

Load Flow Report Manager
Load flow output reports are provided in two forms: ASCII text files and Crystal Reports. The Report
Manager provides four pages (Complete, Input, Result, and Summary) for viewing the different parts of
the output report for both text and Crystal Reports. Available formats for Crystal Reports are displayed in
each page of the Report Manager for load flow studies.

Choosing any format other than TextRept in the Report Manager activates the Crystal Reports. You can
open the whole load flow output report or only a part of it, depending on the format selection. The format
names and corresponding output report sections are given below:
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Branch
Bus
Cable
Complete
Cover
EqCable
LFreport
Losses
Summary
XFMR&X
Loading
UndrOver

Branch input data
Bus input data
Cable input data
Complete output report including all input and output
Title page of the output report
Equipment cable input data
Load Flow calculation results
Branch loss results
Summary of load flow calculation
Transformer and reactor input data
Branch loading results
Bus undervoltage/overvoltage report

You can also view output reports by clicking on the View Output Report button on the Study Case
Toolbar. A list of all output files in the selected project directory is provided for short-circuit
calculations. To view any of the listed output reports, click on the output report name, and then click on
the View Output Report button.

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Toolbar

Load flow text output reports (with an .lfr extension) can be viewed by any word processor such as
Notepad, WordPad, and Microsoft Word. Currently, by default, the output reports are viewed by
Notepad. You can change the default viewer in the ETAPS.INI file to the viewer of your preference
(refer to Chapter 1).
The text output reports are 132 characters wide with 66 lines per page. For the correct formatting and
pagination of output reports, you MUST modify the default settings of your word processor application.
For Notepad, WordPad, and Microsoft Word applications, recommended settings are explained in the
Printing & Plotting section.

Halt Current Calculation
The Stop Sign button is normally disabled. When a short-circuit calculation has been initiated, this button
becomes enabled and shows a red stop sign. Clicking on this button will terminate the calculation.

Get Online Data
When PowerStation Management System is set-up, and the Sys Monitor presentation is on-line, you can
bring real-time data into your off-line presentation and run a Load Flow by pressing on this button. You
will notice that the Operating Loads, Bus Voltages, and Study Case Editor will be updated with the online data.

Get Archived Data
When ETAPS Playback is set-up, and any presentation is on Playback mode, you can bring this data into
your presentation and run a Load Flow by pressing on this button. You will notice that the Operating
Loads, Bus Voltages, and Study Case Editor will be updated with the playback data.

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Study Case Editor

15.2 Study Case Editor
The Load Flow Study Case Editor contains solution control variables, loading conditions, and a variety of
options for output reports. PowerStation allows you to create and save an unlimited number of study
cases. Load flow calculations are conducted and reported in accordance with the settings of the study
case selected in the toolbar. You can easily switch between study cases without the trouble of resetting
the study case options each time. This feature is designed to organize your study efforts and save you
time.
As a part of the multi-dimensional database concept of PowerStation, study cases can be used for any
combination of the three major system toolbar components, i.e. for any configuration status, one-line
diagram presentation, and Base/Revision data.
When you are in Load Flow Analysis mode, you can access the Load Flow Study Case Editor by clicking
on the Study Case button from the Load Flow Study Case Toolbar. You can also access this editor from
the Project View by clicking on the Load Flow Study Case folder.

To create a new study case, go to the Project View, right-click on the Load Flow Study Case folder, and
select Create New. The program will then create a new study case, which is a copy of the default study
case, and adds it to the Load Flow Study Case folder.

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Study Case Editor

15.2.1 Info Page

Study Case ID
Study case ID is shown in this entry field. You can rename a study case by simply deleting the old ID
and entering the new ID. Study case ID can be up to 12 alphanumeric characters. Use the Navigator
button at the bottom of the editor to go from one study case to the next existing study case.

Method
In this section you can select a load flow solution method. Three methods are available: NewtonRaphson, Fast-decoupled, and Accelerated Gauss-Seidel.
Note that for the Newton-Raphson, a few Gauss-Seidel iterations are made first to establish a set of sound
initial values for the bus voltages (since convergence of the Newton-Raphson method is highly dependent
on the initial bus voltages).

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Study Case Editor

Maximum Iteration
Enter the maximum number for iterations. If the solution has not converged before the specified number
of iterations, the program will stop and inform the user. The recommended and default values are 2000
for the Gauss-Seidel method, and five for the Newton-Raphson and Fast-decoupled methods.

Precision
Enter the value for the solution precision, which is used to check for convergence. This value determines
how precise you want the final solution to be. For the Gauss-Seidel method, precision is applied to check
the difference between the bus voltages after each iteration. For the Newton-Raphson and Fast-decoupled
methods, the precision is compared with the difference in power for each bus (MW and Mvar) between
iterations. If the difference between the iterations is less than or equal to the value entered for precision,
the desired accuracy is achieved.
If the solution converges but the mismatch values are high, reduce the value of the precision to make your
results more precise and run the program again (you may need to increase the number of iterations). Note
that a smaller precision value results in lower mismatch (higher accuracy), as well as a longer run time.
The default (and recommended) values are 0.000001 pu volts for the Gauss-Seidel method, and .001 pu
power for the Newton-Raphson and Fast-decoupled methods.

Acceleration Factor
This field is present if the Accelerated Gauss-Seidel method is used. Enter the convergence acceleration
factor to be used between iterations. Typical values are between 1.2 and 1.7; the default is 1.45.

Apply XFMR Phase-Shift
Check this box to consider transformer phase-shift in load flow calculations. The phase-shift of a
transformer can be found from the transformer editor.

Loading
In the Loading section of the Load Flow Study Case Editor, you can specify the operating loads by
selecting a loading category and diversity factors (variable or fixed).

Loading Category
Select one of the ten Loading Categories for this Load Flow Study. With the selection of any category,
PowerStation uses the percent loading of individual motors and other loads as specified for the selected
category. Note that you can assign loading to each one of the ten categories from the Nameplate page of
the induction machine editor and synchronous motor editor and the Loading or Rating page of other load
component editors.

Operating Load
This option is available if your ETAP key has the online feature. When this box is checked, the operating
loads updated from online data or a previous load flow study will be utilized in the load flow study.

Load Diversity Factor
This section allows you to specify load diversity factors to be applied on the loading category load. When
the Operating Load is selected, no diversity factor is considered.

None
Select None to use the percent loading of each load as entered for the selected Loading Category.

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Study Case Editor

Bus Maximum
When the Maximum Loading option is selected, all motors and other loads directly connected to each bus
will be multiplied by the bus maximum diversity factor. Using this option, you can simulate load flow
studies with each bus having a different maximum diversity factor.
This study option is helpful when the future loading of the electrical system has to be considered and each
bus may be loaded at a different maximum value.

Bus Minimum
When the Minimum Bus Loading option is selected, all motors and other loads directly connected to each
bus will be multiplied by the bus minimum diversity factor. Using this option, you can simulate load
flow studies with each bus having a different minimum diversity factor.
The minimum bus loading study option may be used to see the effect of transformer taps and capacitors
(if any) on the system voltages under a minimum (light) loading condition.

Global Diversity Factor
Enter the diversity factors for all constant kVA and constant Z loads. When you select this option,
PowerStation will globally multiply all motors and static loads of the selected Loading Category with the
entered values for the motor and static load diversity factors.
Note that a motor load-multiplying factor of 125% implies that the motor loads of all buses are increased
by 25 percent above their nominal values. This value can be smaller or greater than 100 percent.

Charger Loading
For chargers, you have the option to use the loading category load or the operating load. Note that the
operating load for a charger can only be updated from a DC load flow study.

Initial Condition
Initial conditions for all bus voltages and angles can be specified in this section for load flow calculation
purposes.

Use Bus Voltages
Select this option to use bus voltages and angles as entered in the Info page of the bus editors. Using this
option you can simulate load flow studies with different initial conditions for bus voltage.

Use Fixed Values
This option allows you to simulate load flow studies using a fixed bus voltage and angle for all buses.
When you select the fixed initial condition option, you must enter the initial voltage value as the percent
of the bus nominal voltage. The default values are 100% for bus voltage magnitude and zero degree for
bus voltage angle.

Determination of Initial Bus Voltage Angle
When transformer phase-shift is considered in the load flow calculation, the initial bus voltage angle
should take it into account. Otherwise, very poor initial bus voltage angle may be used and will affect
load flow convergence. To resolve this issue, ETAP load flow program calculates the bus voltage angle
based on transformer phase-shift and compare the calculated value against the initial bus voltage angle
from user selected option. If the difference between the two values is larger than MaxIniAngDiff, ETAP
uses the calculated the values as the initial bus voltage angle, where MaxIniAngDiff is an ETAP.INI file

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Study Case Editor

entry defaulted at 10. According to the selection for the initial bus voltage and the Apply XFMR PhaseShift field, there are four different situations:
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When the Use Fixed Values is checked and the Apply XFMR Phase-Shift is also checked, the
calculated initial bus voltage angles are used in the load flow calculation.
When the Use Bus Voltages is checked and the Apply XFMR Phase-Shift is also checked, the initial
bus voltage angle from the Bus Editor is compared against the calculated bus voltage angle. If the
difference is less than MaxIniAngDiff, the initial bus voltage angle from the Bus Editor is used;
otherwise the calculated value is used in the load flow calculation.
When the Use Fixed Values is checked and the Apply XFMR Phase-Shift is not checked, the initial
voltage angle entered in the Load Flow Study Case is used in the load flow calculation. In this case,
all the buses have the same initial voltage angle.
When the Use Bus Voltages is checked and the Apply XFMR Phase-Shift is not checked, the initial
bus voltage angles from the Bus Editor are used in the load flow calculation.

When the operating load is specified as the system load, the operating voltage angles are used as the
initial value. In this case, if the Apply XFMR Phase-Shift is checked, the operating voltage angle is
compared against the calculated bus voltage angle. If the difference is less than MaxIniAngDiff, the
operating voltage angle is used; otherwise the calculated value is used in the load flow calculation.

Report
Equipment Cable Losses and Vd
Select this option to report losses and voltage drop associated with equipment cables in the output report.

Bus Voltage
Calculated bus voltages seen in the output report can be printed in kV or in percent of the bus nominal
voltages. Select your preference by clicking on in Percent or in kV. For graphical display of bus
voltages see Load Flow Display Options.

Update
In this section, you can decide to update initial conditions of the buses and/or set the transformer taps to
the calculated value of LTCs. The selected options will be updated after the subsequent load flow run.

Initial Bus Voltage
Select this option to update the values of the bus voltage magnitudes with the result of this load flow run.
Bus voltage update will result in a faster convergence of the subsequent load flow solutions since the
initial bus voltages will be closer to the final values.

Inverter Operating Load
In an AC load flow study, an inverter is represented as a constant voltage source. When this option is
checked, the load provided by the inverter will be updated to the inverter element, which can be used later
as DC load of the inverter in a DC load flow study.

Operating Load & V
The option is available if your ETAP key has the online feature. When this box is checked, the
calculation results will be updated to sources, loads, and buses, so that they can be utilized as input for
later studies. These values are also displayed in element editors. If your ETAP key does not have the

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Study Case Editor

online feature, you can see the operating P, Q, and V in only element editors, and they cannot be used in a
later study.

Transformer LTCs
Select this option to update the transformer taps to reflect the result of load tap changer (LTC) settings,
i.e., transformer taps will be set to values determined from the load flow solution for LTCs. This feature
is useful when you want to consider the impedance of the LTC taps for short-circuit calculations.

Remarks 2nd Line
You can enter up to 120 alphanumeric characters in this remarks box. Information entered in this location
will be printed on the second line of every output page header line. These remarks can provide specific
information for each study cases. Note that the first line of the header information is global for all study
cases and is entered in the Project Information Editor.

15.2.2 Alert Page
The Alert Page in the Load Flow Study Case Editor is used to specify the setup of all the Simulation
Alerts provided to notify the user of an abnormal loading condition based on predetermined, “allowable”,
percent values and system topology. The functional capability of the Simulation Alert System is to
generate alerts when there is an overload in protective devices, buses, transformers, cables, reactors,
generators, and utilities. The alerts are reported by the generation of different types of alerts, either
graphically in the one-line diagram display or in the Alert View Window.

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Study Case Editor

Critical and Marginal Alerts
There are two types of simulation alerts generated after a Load Flow study. The difference between
Marginal and Critical Alerts is their use of different percent value conditions to determine if an alert
should be generated. If a condition for a Critical alert is met, then an alert will be generated in the Alert
View Window and the overloaded element will turn red in the one-line diagram. The same is true for
Marginal Alerts, except that the overloaded component will be displayed in magenta color. Also, the
Marginal Alerts check box must be selected if the user desires to display the Marginal Alerts. If a device
alert qualifies it for both Critical and Marginal alerts, only Critical Alerts are displayed. It should be
noted that in order for ETAP PowerStation to generate alerts for an element type, both the element rating
and the percent value entered in this page must be non-zero. The element ratings for alert checking are
given in the following sections.

Loading
This set of value fields allows the user to enter the condition percent values of the monitored parameters
used to determine if an alert should be reported based on loading conditions determined by a Load Flow
calculation. The Load Flow Loading Alerts generate overload alerts.

Bus Alerts
Bus loading alerts are determined from the values entered into the percent value input fields. The
monitored parameter is the percent of rated continuous current flowing through the bus. If the continuous
current calculated from a Load Flow study exceeds the specified percent values, then the program
generates an alert.

Transformer Alerts
Transformer Simulation Alerts generate an alert if the Critical or Marginal percent limit of maximum
MVA rating is exceeded after a Load Flow calculation. If the calculated MVA is more than the percent of
rated value specified in the Marginal or Critical percent fields, overload alerts are reported. The
simulation alerts work for both two and three winding transformers.

Cable
Cable Simulation Alerts monitor the rated loading limit for cables / line in percent of allowable ampacity,
which is entered from the Ampacity Page of the Cable Editor. If the Load Flow calculated current
percent flowing through the cable is greater than the Marginal or Critical percent limits, overload alerts
are reported.

Reactor
A reactor alert generates alerts if the program determines that the percent of rated continuous current is
exceeded based on the Load Flow calculation results. These alerts are reported as overloads.

Generator / Utility
The generator Loading Simulation Alert monitors the percent of rated MW. If the results from a Load
Flow calculation indicate that the specified percent of rated MW is exceeded, then, the program reports an
overload alert.

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Study Case Editor

Protective Devices
Protective Device Simulation Alerts generate alerts when certain predetermined parameter value ratings
are exceeded. The following table contains a list of the conditions used by the Alert Simulation Program
to determine when to report an alert. Load Flow results are compared to the monitored parameters listed
in the following table:
Protective Devices
Low Voltage Circuit Breaker
High Voltage Circuit Breaker
Fuses
Contactors
SPDT / SPST switches

Monitored parameters in
percent of
Continuous rated Current
Continuous rated Current
Rated Current
Continuous rated Current
Continuous rated Current

Condition reported
Overload
Overload
Overload
Overload
Overload

Protective device alerts will generate alerts only if the monitored parameter rating is larger than zero.

Bus Voltage Alerts
Bus Voltage Simulation Alerts generate alerts if the voltage magnitude percent results from the Load
Flow calculation exceed or are below the specified nominal kV rating percent values. Bus Voltage Alerts
report over voltage and under voltage alerts.

Generator / Utility Excitation Alerts
Simulation Alerts for generator excitation, monitor the percent rated Mvar limits. An alert for Over
Excitation is reported if the Upper Excitation percent limit (Qmax) for the generator is exceeded
according to a Load Flow calculation. An alert for Under Excitation is reported if the generator Mvar
result from the Load Flow calculation is below the specified Lower Excitation percent limit (Qmin).

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Display Options

15.3 Display Options
15.3.1 Results Page
The Load Flow Analysis Display Options consist of a Results page and three pages for AC, AC-DC, and
DC info annotations. Note that the colors and displayed annotations selected for each study are specific
to that study.

Color
Select the color for result annotations to be displayed on the one-line diagram.

Voltage
Voltage
Select kV or percent for voltage display on the one-line diagram from the list. It should be noted that all
percent voltages are displayed with the bus nominal kV as the base voltage.

Bus
Select this option to display bus voltages on the one-line diagram. Bus voltages are displayed at 15
degrees.

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Display Options

Load Term
Select this option to display load (motors and static loads) terminal voltages on the one-line diagram.
Load terminal voltages are displayed at 15 degrees.

% Voltage Drop
Line / Cable
Select this option to display line and cable voltage drops on the one-line diagram.

Load FDR
Select a unit for power flow or current flow from the list to be displayed on the one-line diagram.

Power Flows
Here you specify how the flows will be displayed.

Units
Select the unit (kVA or MVA) to be used to display power flow on the one-line diagram.

kW + jkvar
Select the kW + jkvar radio button to display power flow in kW+jkvar or MW+jMvar.

kVA
Select the kVA radio button to display power flow in kVA or MVA.

Amp
Select the Amp radio button to display current flow in amperes.

%PF
When the Amp or kVA radio button is selected, you can check this box to show power factor of power
flow along with the current.

Show Units
Select this option to show units for power flow and current displayed on the one-line diagram.

Elements
Branch
Select this option to display power flow through all branches on the one-line diagram. PowerStation
displays the power flow at one end of a branch, i.e., the end that has a positive kW value flowing into the
branch. For three-winding transformers, all three power flows are displayed.

Gen./Motor/Load
Select this option to display power flow for generators, motors, MOVs, capacitors, lumped loads, and
static loads on the one-line diagram.

Composite Motor
Select this option to display power flow into composite motors.

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Display Options

Composite Network
Select the check box to display power flow into composite networks.

Branch Losses
Select this option to display branch losses on the one-line diagram. Losses are displayed inside a bracket
in [kW+jkvar] or [MW+jMvar].

Meters
Ammeter
Check this option to display primary current for the branch to which an ammeter is attached.

Voltmeter
Check this option to display primary voltage for the bus to which a voltmeter is attached.

Multi-Meter
Check this option to display the measurements of a multi-meter, including bus voltage, branch current,
branch power flow, power factor, and frequency.

15.3.2 AC Page
This page includes options for displaying info annotations for AC elements.

Color
Select the color for information annotations to be displayed on the one-line diagram.

ID
Select the check boxes under this heading to display the ID of the selected AC elements on the one-line
diagram.

Rating
Select the check boxes under this heading to display the ratings of the selected AC elements on the oneline diagram.

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Device Type
Generator
Power Grid (Utility)
Motor
Load
Panel
Transformer
Branch, Impedance
Branch, Reactor
Cable / Line
Bus
Node
CB
Fuse
Relay
PT & CT

Display Options

Rating
kW / MW
MVAsc
HP / kW
kVA / MVA
Connection Type (# Phases - # Wires)
kVA / MVA
Base MVA
Continuous Amps
# of Cables - # of Conductor / Cable - Size
kA Bracing
Bus Bracing (kA)
Rated Interrupting (kA)
Interrupting (ka)
50/51 for Overcurrent Relays
Transformer Rated Turn Ratio

kV
Select the check boxes under this heading to display the rated or nominal voltages of the selected
elements on the one-line diagram.
For cables/lines, the kV check box is replaced by the
cable/line conductor type on the one-line diagram.

button. Click on this button to display the

A
Select the check boxes under this heading to display the ampere ratings (continuous or full-load ampere)
of the selected elements on the one-line diagram.
For cables/lines, the Amp check box is replaced by the
cable/line length on the one-line diagram.

button. Click on this button to display the

Z
Select the check boxes under this heading to display the rated impedance of the selected AC elements on
the one-line diagram.
Device Type
Generator
Power Grid (Utility)
Motor
Transformer
Branch, Impedance
Branch, Reactor
Cable / Line

Impedance
Subtransient reactance Xd”
Positive Sequence Impedance in % of 100 MVA (R + j X)
% LRC
Positive Sequence Impedance (R + j X per unit length)
Impedance in ohms or %
Impedance in ohms
Positive Sequence Impedance (R + j X in ohms or per unit length)

D-Y
Select the check boxes under this heading to display the connection types of the selected elements on the
one-line diagram.
For transformers, the operating tap setting for primary, secondary, and tertiary windings are also
displayed. The operating tap setting consists of the fixed taps plus the tap position of the LTC.

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Display Options

Composite Motor
Click on this check box to display the AC composite motor IDs on the one-line diagram, then select the
color in which the IDs will be displayed.

Use Default Options
Click on this check box to use PowerStation’s default display options.

15.3.3 AC-DC Page
This page includes options for displaying info annotations for AC-DC elements and composite networks.

Color
Select the color for information annotations to be displayed on the one-line diagram.

ID
Select the check boxes under this heading to display the IDs of the selected AC-DC elements on the oneline diagram.

Rating
Select the check boxes under this heading to display the ratings of the selected AC-DC elements on the
one-line diagram.
Device Type
Charger
Inverter
UPS
VFD

Rating
AC kVA & DC kW (or MVA / MW)
DC kW & AC kVA (or MW / MVA)
kVA
HP / kW

kV
Click on the check boxes under this heading to display the rated or nominal voltages of the selected
elements on the one-line diagram.

A
Click on the check boxes under this heading to display the ampere ratings of the selected elements on the
one-line diagram.
Device Type
Charger
Inverter
UPS

Amp
AC FLA & DC FLA
DC FLA & AC FLA
Input, output, & DC FLA

Composite Network
Click on this check box to display the composite network IDs on the one-line diagram, then select the
color in which the IDs will be displayed.

Use Default Options
Click on this check box to use PowerStation’s default display options.

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Display Options

15.3.5 DC Page
This page includes options for displaying info annotations for DC elements.

Color
Select the color for information annotations to be displayed on the one-line diagram.

ID
Select the check boxes under this heading to display the IDs of the selected DC elements on the one-line
diagram.

Rating
Select the check boxes under this heading to display the ratings of the selected DC elements on the oneline diagram.
Device Type
Battery
Motor
Load
Elementary Diagram
Converter
Cable

Rating
Ampere Hour
HP / kW
kW / MW
kW / MW
kW / MW
# of Cables - # of Conductor / Cable - Size

kV
Select the check boxes under this heading to display the rated or nominal voltages of the selected
elements on the one-line diagram.
For cables, the kV check box is replaced by the
type on the one-line diagram.

button. Click on this button to display the conductor

A
Select the check boxes under this heading to display the ampere ratings of the selected elements on the
one-line diagram.
For cables, the Amp check box is replaced by the
button. Click on this button to display the cable
length (one way) on the one-line diagram.

Z
Select the check boxes under this heading to display the impedance values of the cables and impedance
branches on the one-line diagram.

Composite Motor
Click on this check box to display the DC composite motor IDs on the one-line diagram, then select the
color in which the IDs will be displayed.

Use Default Options
Click on this check box to use PowerStation’s default display options.

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ETAP PowerStation 4.0

Load Flow Analysis

Calculation Methods

15.4 Calculation Methods
PowerStation provides three load flow calculation methods: Newton-Raphson, Fast-Decoupled, and
Accelerated Gauss-Seidel. They possess different convergent characteristics, and sometimes one is
more favorable in terms of achieving the best performance. You can select any one of them depending on
your system configuration, generation, loading condition, and the initial bus voltages.

Newton-Raphson Method
The Newton-Raphson method formulates and solves iteratively the following load flow equation:
 ∆P   J 1
 ∆Q   J
  3

J 2   ∆δ 
=
J 4   ∆V 

where ∆P and ∆Q are bus real power and reactive power mismatch vectors between specified value and
calculated value, respectively; ∆V and ∆δ represents bus voltage angle and magnitude vectors in an
incremental form; and J1 through J4 are called Jacobian matrices.
The Newton-Raphson method possesses a unique quadratic convergence characteristic. It usually has a
very fast convergence speed compared to other load flow calculation methods. It also has the advantage
that the convergence criteria are specified to ensure convergence for bus real power and reactive power
mismatches. This criteria gives you direct control of the accuracy you want to specify for the load flow
solution. The convergence criteria for the Newton-Raphson method are typically set to 0.001 MW and
Mvar.
The Newton-Raphson method is highly dependent on the bus voltage initial values. A careful selection of
bus voltage initial values is strongly recommended. Before running load flow using the Newton-Raphson
method, PowerStation makes a few Gauss-Seidel iterations to establish a set of sound initial values for the
bus voltages.
The Newton-Raphson method is recommended for use with any system as a first choice.

Fast-Decoupled Method
The Fast-decoupled method is derived from the Newton-Raphson method. It takes the fact that a small
change in the magnitude of bus voltage does not vary the real power at the bus appreciably, and likewise,
for a small change in the phase angle of the bus voltage, the reactive power does not change appreciably.
Thus the load flow equation from the Newton-Raphson method can be simplified into two separate
decoupled sets of load flow equations, which can be solved iteratively:

[ ∆P ] = [J1 ][ ∆δ ]
[ ∆Q] = [J 4 ][ ∆V ]
The Fast-decoupled method reduces computer memory storage by approximately half, compared to the
Newton-Raphson method. It also solves the load flow equations using significantly less computer time
than that required by the Newton-Raphson method, since the Jacobian matrices are constant.
As with the Newton-Raphson method, convergence criteria of the Fast-decoupled method is based on real
power and reactive power mismatches, which are typically set to 0.001 in the order of MW and Mvar.

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ETAP PowerStation 4.0

Load Flow Analysis

Calculation Methods

Although for a fixed number of iterations it is not as accurate as the Newton-Raphson method, the savings
in computer time and the more favorable convergence criteria makes for a very good overall performance.
In general, the Fast-decoupled method can be used as an alternative to the Newton-Raphson method, and
it should definitely be given a try if the Newton-Raphson method has failed when dealing with long radial
systems or systems that have long transmission lines or cables.

Accelerated Gauss-Seidel Method
From the system nodal voltage equation

[I ] = [YBUS ][V ]
the Accelerated Gauss-Seidel method derives the following load flow equation and solves it iteratively:
*
[P + jQ] = [V T ][YBUS
][V * ]

where ∆P and ∆Q are specified bus real and reactive power vectors, ∆V is the bus voltage vector, and
YBUS is the system admittance matrix.
The Accelerated Gauss-Seidel method has relatively lower requirements of the bus initial voltage values
compared to the Newton-Raphson method and the Fast-decoupled method. Instead of using bus real
power and reactive power mismatch as convergence criteria, the Accelerated Gauss-Seidel method checks
bus voltage magnitude tolerance between two consecutive iterations to control the solution precision. The
typical value for bus voltage magnitude precision is set to 0.000001 pu.
The Accelerated Gauss-Seidel method has slower convergence speed. When you apply appropriate
acceleration factors, a significant increase in the rate of convergence can be obtained. The range for the
acceleration factor is between 1.2 and 1.7, and is typically set to 1.45.

Load Flow Convergence
As in any iterative solution method, the convergence of the load flow solution is affected by a number of
factors specific to power systems.

Negative Impedance
Negative resistance and reactance should be avoided. As an example, the traditional method of modeling
three-winding transformers by a Y equivalent model, using one impedance and two two-winding
transformers, sometimes results in a negative impedance value for one of the impedance branches. In this
case, the negative impedance should be combined with other series circuit elements so that the result is a
positive impedance value. Load flow calculations may not converge if a large value of negative
impedance is used. PowerStation can now model three-winding transformers directly with no need for
the user to do any conversions.

Zero or Very Small Impedance
A zero or very small impedance value of any branch is not allowed, since this will result in infinity or a
huge number in the system admittance matrix. You should represent this type of impedance by a tie
circuit breaker to solve the problem.

Operation Technology, Inc.

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ETAP PowerStation 4.0

Load Flow Analysis

Calculation Methods

Widely Different Branch Impedance Values
Widely different branch impedance values on the same per unit base may result in a slow convergence.
To avoid this situation, various techniques, such as combining series branches with low impedance
values, ignoring short length transmission lines and/or cables, or modeling a small impedance branch with
tie circuit breakers, can be employed.

Long Radial System Configurations
Long radial system configurations usually take a longer time to converge than loop configurations. In
general, the Fast-decoupled method works faster than the Newton-Raphson or the Accelerated GaussSeidel method for radial system.

Bad Bus Voltage Initial Values
Solution convergence speed and computing time are functions of the initial voltages for load-type buses.
The closer the initial voltages are to their final profile, the faster the solution converges. The solution
may not converge if the initial voltages are too far from the final profile, thus it is recommended that the
Update Bus Voltage option be used to obtain a set of sound initial bus voltages.

Modeling of AC-DC Converters
In a load flow study, chargers and UPSs are represented as constant kVA loads connected to their AC
input bus. An inverter is represented as a swing machine, which can maintain its terminal bus angle and
voltage magnitude constant. If you have more than one inverters connected to a bus, they will equally
share the load.
Variable frequency drives are not considered in the load flow study.
frequency drive is directly added to its terminal bus.

The load behind a variable

Different Factors Considered in Load Calculation
PowerStation provides users with great flexibility in modeling load variations through different load
factors, such as demand factor, load percent, service factor, and application factor, etc. Depending on
user specifications, these factors are used differently in calculating loads under several circumstances:
•
•
•
•

Load Editor – Calculation of load for loading categories and voltage drop
Input for Studies – Calculation of load specification for load flow and initial load for motor starting
and transient stability studies
Studies Results – Calculation of load displayed in one-line diagram from load flow, motor starting,
and transient stability studies
Bus Editor – Sum of load connected to a bus

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ETAP PowerStation 4.0

Load Flow Analysis

Calculation Methods

The following two tables describe how these factors are used in these cases:

Factors Used for Motor Load Calculation
Load Editor
Load Loss Vd
Bus Nominal kV

x

x

Bus Operating V

x

x

Input to Studies
Load
Loss
x

x

Results from Studies
Load
Loss
Vd
x

x

x

x

x

x

Bus
Editor
x

Demand Factor

x

x

x

x

x

x

x

x

x

Loading %

x

x

x

x

x

x

x

x

x

x

x

x

x

Bus Diversity Factor

*

*

*

*

*

Global Diversity Factor

*

*

*

*

*

Service Factor

*

App. Factor

*

Load Quantity

x

x

x

Factors Used for Static Load Calculation
Load Editor
Load Loss Vd
Bus Nominal kV

x

x

Bus Operating V

x

Input to Studies
Load
Loss
x

x

x

Results from Studies
Load Loss
Vd
x

x

x

x

x

x

Bus
Editor
x

Demand Factor

x

x

x

x

x

x

x

x

x

Loading %

x

x

x

x

x

x

x

x

x

x

x

x

x

*

*

*

*

App. Factor
Load Quantity
Bus Diversity Factor

*
x

x

x
*

Global Diversity Factor
*
*
*
*
*
* Indicates the factor is used in calculation if specified by the user in the related load editor or study case.
Notes:
•
•

Motor load includes induction motor and generator, synchronous motor, MOV, and motor load
portion of lumped load.
Static load includes static load, capacitor, and static load portion of lumped load

Operation Technology, Inc.

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ETAP PowerStation 4.0

Load Flow Analysis

Required Data

15.5 Required Data
Bus Data
Required data for load flow calculations for buses includes:
•
•
•

Nominal kV
%V and Angle (when Initial Condition is set to use Use Bus Voltages)
Load Diversity Factor (when the Loading option is set to use Diversity Factor)

Branch Data
Branch data is entered into the Branch Editors, i.e., Transformer, Transmission Line, Cable, Reactor, and
Impedance Editors. Required data for load flow calculations for branches includes:
•
•
•
•

Branch Z, R, X, or X/R values and units, tolerance, and temperature, if applicable
Cable and transmission line, length, and unit
Transformer rated kV and kVA/MVA, tap, and LTC settings
Impedance base kV and base kVA/MVA

Power Grid Data
Required data for load flow calculations for power grids includes:
•
•
•
•
•

Operating mode (Swing, Voltage Control, or Mvar Control)
Nominal kV
%V and Angle for swing mode
%V, MW loading, and Mvar limits (Qmax & Qmin) for voltage control mode of operation
MW and Mvar loading for Mvar control mode

Synchronous Generator Data
Required data for load flow calculations for synchronous generators includes:
•
•
•
•
•

Operating mode (Swing, Voltage Control or Mvar Control)
Rated kV
%V and Angle for swing mode of operation
%V, MW loading, and Mvar limits (Qmax & Qmin) for Voltage Control mode of operation
MW and Mvar loading for Mvar control mode of operation

Inverter Data
Required data for load flow calculations for inverters includes:
•
•
•

Inverter ID
DC and AC rating data
AC output voltage regulating data

Operation Technology, Inc.

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ETAP PowerStation 4.0

Load Flow Analysis

Required Data

Synchronous Motor Data
Required data for load flow calculations for synchronous motors includes:
•
•
•
•

Rated kW/hp and kV
Power factors and efficiencies at 100%, 75%, and 50% loadings
Loading Category ID and % Loading
Equipment cable data

Induction Motor Data
Required data for load flow calculations for induction motors includes:
•
•
•
•

Rated kW/hp and kV
Power factors and efficiencies at 100%, 75%, and 50% loadings
Loading Category ID and % Loading
Equipment cable data

Static Load Data
Required data for load flow calculations for static loads includes:
•
•
•
•
•

Static Load ID
Rated kVA/MVA and kV
Power factor
Loading Category ID and % Loading
Equipment cable data

Capacitor Data
Required data for load flow calculations for static loads includes:
•
•
•
•

Capacitor ID
Rated kV, kvar/bank, and number of banks
Loading category ID and % Loading
Equipment cable data

Lumped Load Data
Required data for load flow calculations for static loads includes:
•
•
•

Load ID
Rated kV, MVA, power factor, and % motor load
Loading category ID and % Loading

Charger & UPS Data
Required data for load flow calculations for chargers and UPSs includes:
•
•
•

Element ID
Rated AC kV, MVA, and power factor, as well as DC rating data
Loading category ID and % Loading

Operation Technology, Inc.

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ETAP PowerStation 4.0

Load Flow Analysis

Required Data

Other Data
There are some study case related data, which must also be provided. This includes:
•
•
•
•
•
•
•
•

Method (Newton-Raphson, Fast-decoupled, or Accelerated Gauss-Seidel)
Max Iteration
Precision
Acceleration Factor (when Accelerated Gauss-Seidel method is selected)
Loading Category
Initial Condition
Report (report format)
Update (for bus voltages and transformer LTCs using load flow result)

The study case related data is entered into the Load Flow Study Case Editor.

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ETAP PowerStation 4.0

Load Flow Analysis

Output Reports

15.6 Output Reports
The load flow calculation results are reported both on the one-line diagram and in the Crystal Reports
format. The graphical one-line diagram displays the calculated bus voltages, branch flows and voltage
drops, load power consumption, etc. You can use the Display Options Editor to specify the content to be
displayed. It also flags abnormal operating conditions, such as overloaded cables and over- or
undervoltage buses, in different colors.
The Crystal Reports format provides you with detailed information for a load flow analysis. You can
utilize the Load Flow Report Manager to help you view the output report.

15.6.1 View from Study Case Toolbar
This is a shortcut for the Report Manger. When you click on the View Output Report button,
PowerStation automatically opens the output report listed in the Study Case Toolbar with the selected
format. In the picture shown below, the output report name is LF-Winter and the selected format is Text
Report.

15.6.2 Report Manager
To open the Report Manager, simply click on the View Report Manager button on the Load Flow
Toolbar. The editor includes four pages (Complete, Input, Result, and Summary) representing different
sections of the output report. The Report Manager allows you to select formats available for different
portions of the report and view it via Crystal Reports. There are several fields and buttons common to
every page, as described below.

Output Report Name
This field displays the name of the output report you want to view.

Project File Name
This field displays the name of the project file based on which report was generated, along with the
directory where the project file is located.

Help
Click on this button to access Help.

OK / Cancel
Click on the OK button to dismiss the editor and bring up the Crystal Reports view to show the selected
portion of the output report. If no selection is made, it will simply dismiss the editor. Click on the Cancel
button to dismiss the editor without viewing the report.
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ETAP PowerStation 4.0

Load Flow Analysis

Output Reports

15.6.3 Input Data
This page allows you to select different formats for viewing input data, grouped according to type. They
include:
Branch
Bus
Cable
Cover
EqCable
XFMR&X

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ETAP PowerStation 4.0

Load Flow Analysis

Operation Technology, Inc.

Output Reports

15-28

ETAP PowerStation 4.0

Load Flow Analysis

Output Reports

15.6.4 Results
This page allows you to select formats to view the load flow result portion of the output report.

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ETAP PowerStation 4.0

Load Flow Analysis

Operation Technology, Inc.

Output Reports

15-30

ETAP PowerStation 4.0

Load Flow Analysis

Output Reports

15.6.5 Summary
This page allows you to select different portions of the load summary to view. Note that some portions of
the summary are available only when you selected specific options in the study case, such as Critical and
Marginal Voltage options.
Alert-Complete
Alert-Critical
Alert-Marginal
Branch Loading
Bus Loading
Losses
Summary

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Load Flow Analysis

Operation Technology, Inc.

Output Reports

15-32

ETAP PowerStation 4.0

Load Flow Analysis

Output Reports

15.6.6 Complete
In this page you select from the formats available, Complete, which brings up the complete report for the
load flow study, or Text Report, which is explained in greater detail in the Text Report section. The
complete report includes input data, results, and summary reports.

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Load Flow Analysis

Operation Technology, Inc.

Output Reports

15-34

ETAP PowerStation 4.0

Load Flow Analysis

Output Reports

15.6.7 Text Report
The text report is a continuous ASCII file that contains input data, results, and summary reports. Text
reports can be viewed by any word processor as specified in the PowerStation INI file. The default word
processor PowerStation uses to view text reports is set to Notepad. For more information see the Printing
and Plotting chapter.
PowerStation provides load flow study output reports with different levels of detail, depending on your
requirements. The following are some sample output reports.

Sample 1: Input Data
This section lists system input parameters for buses; transmission lines & cables; transformers, reactors,
& impedances; and all connections including tie circuit breakers, fuses, and switches.
Bus Information & Nominal kV
================================================

Init. Voltage

Generation

Motor Load

Static Load

Mvar Limits

=============

==============

==============

==============

==============

ID

Type

kV

Description

% Mag.

Ang.

MW

Mvar

MW

Mvar

MW

Mvar

Max.

Min.

------------

----

------

--------------------

------

-----

------

------

------

------

------

------

------

------

Bus3

Load

13.800

101.0

-1.2

3.368

1.355

0.000

0.000

LVBus

Load

0.480

99.1

-1.8

0.121

-0.059

0.250

0.127

Main Bus

SWNG

34.500

100.0

0.0

0.000

0.000

0.000

0.000

MCC1

Load

0.480

98.0

-3.0

0.421

0.190

0.200

0.000

Sub 2A

Load

13.800

101.5

-1.3

0.000

0.000

0.000

0.000

Sub 2B

Gen.

13.800

100.0

1.4

0.996

-0.616

0.000

0.000

4.650

-2.000

Sub 3

Load

4.160

99.8

-0.4

0.000

0.000

0.000

0.000

Sub3 Swgr

Load

4.160

99.6

-0.4

LV Motor Control Cen

6.300

------------------------------------------------8 Buses Total
CKT / Branch
============

Line / Cable

0.000

0.400

0.170

0.000

0.000

------

------

------

------

------

6.300

5.306

1.040

0.450

0.127

(ohms/1000 ft per phase)

Impedance

===================================================================

===================================

ID

Library

Size

L (ft)

#/í

T (øC)

R

X

Y

MVAb

% R

% X

% Y

------------

--------

----

------

---

------

--------

--------

--------

-------

-------

-------

----------

1350.

1

75

0.20200

0.06850 0.0000000

100.0

14.32

4.86

0.0000000

250.

1

75

0.03860

0.04270 0.0000000

100.0

5.58

6.17

0.0000000

Cable11

15MCUS1

Cable2

5MCUS3

2
350

CKT / Branch
============

Transformer
=======================================

%Tap Setting

Reactor

Impedance (100 MVA Base)

=============

=================

========================

ID

MVA

kV

kV

% Z

X/R

From

------------

-------

------

------

-------

-----

T3

1.000

4.160

0.480

6.500

18.0

0.000

XFMR 3

1.000

4.160

0.480

7.200

28.0

0.000

T2

10.000

34.500

13.800

6.900

23.0

-2.500

T1

15.000( base MVA for 3-Winding )

To

X (ohm)

X/R

% Tol.

% R

% X

--------

-------

------

-------

-------

0.000

0.00

36.1

649.0

0.000

0.00

25.7

719.5

0.000

0.00

3.0

68.9

------ ------

15.000

34.500

Zps =

7.100

39.0

0.000

0.00

1.2

47.3

10.000

13.800

Zpt =

7.200

40.0

0.000

0.00

1.2

48.0

5.000

4.160

Zst =

14.100

38.0

0.000

0.00

2.5

94.0

CKT / Branch

Connected Bus ID

%Impedance (100 MVA Base)

========================

==========================

=========================

ID

Type

From

To

R

X

Z

-------

-------

-------

14.3

4.9

15.1

5.6

6.2

8.3

------------

----------

------------

------------

Cable11

Line/Cable

Sub 2A

Bus3

Cable2

Line/Cable

Sub 3

Sub3 Swgr

T3

2W XFMR

Sub3 Swgr

LVBus

36.1

649.0

650.0

XFMR 3

2W XFMR

Sub3 Swgr

MCC1

25.7

719.5

720.0

T2

2W XFMR

Main Bus

Sub 2A

2.9

67.2

67.3

T1

3W XFMR

Main Bus

Sub 2B

1.2

48.0

48.0

Main Bus

Sub 3

1.2

48.7

48.7

Sub 2B

Sub 3

324.1

3383.4

3398.9

Sub 2A

Sub 2B

0.0

0.0

0.0

Tie CB

Tie Breakr

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ETAP PowerStation 4.0

Load Flow Analysis

Output Reports

Sample 2: Load Flow Report
This section tabulates detailed load flow results. It gives bus ID, type, and nominal kV, calculated
voltage magnitudes and angles, MW and Mvar generation and loading, and the branch flows from the bus
to all buses connected to it. Flows are given in MW and Mvar, amperes and %PF measured at the bus.
Flows into 3-winding transformers are indicated as flows from one of the bus windings to the other two
bus windings, e.g., form Main Bus to Sub 2B and Sub 3. The settings of tap-changing transformers are
also indicated at buses to which a tap side is connected. These tap settings include the fixed taps and
results from the LTCs. Regulated (voltage-controlled) buses are flagged with a *.
Bus Information & Nom kV

Voltage

Generation

Motor Load

========================

===========

============

============

ID

Type

Static

Load

============

Load Flow

XFRM

======================================

kV

% Mag. Ang.

MW

Mvar

MW

Mvar

MW

Mvar

To Bus ID

MW

Mvar

Amp

------------ ----

-----

------ ----

-----

-----

-----

-----

-----

-----

------------

-----

-----

---- -----

Bus3

Load

13.80

0.3

0.00

0.00

3.37

1.35

0.00

0.00

Sub 2A

-3.37

-1.35

152

92.8

LVBus

Load

0.48

99.06 -1.8

0.00

0.00

0.12

-0.06

0.25

0.12

Sub3 Swgr

-0.37

-0.07

451

98.4

Swng

34.50

-0.53

3.31

0.00

0.00

0.00

0.00

Sub 2A

-0.69

3.42

Sub 2B

0.16

-0.11

-0.61

-0.19

787

95.5

152

92.8

*Main Bus

99.74

100.00

0.0

%PF

=====
% Tap
-----

58 -19.8 -2.500
3 -82.9

Sub 3
MCC1

Load

0.48

Sub 2A

Load

13.80

Sub 2B

Load

13.80

98.00 -3.0
100.29

100.29

0.3

0.3

0.00

0.00

0.42

0.19

0.19

0.00

Sub3 Swgr

0.00

0.00

0.00

0.00

0.00

0.00

Bus3

3.39

1.36

Main Bus

0.69

-3.34

142 -20.3

Sub 2B

-4.08

1.98

189 -90.0

Sub 2A

4.08

-1.98

189 -90.0

Sub 3

1.22

0.59

56

90.0

6.30

-2.00

1.00

-0.62

0.00

0.00

Main Bus
Sub 3

Load

4.16

99.76 -0.4

0.00

0.00

0.00

0.00

0.00

0.00

Sub3 Swgr

1.38

0.47

202

94.7

Main Bus

-1.38

-0.47

202

94.7

Sub 3

-1.38

-0.47

202

94.8

LVBus

0.37

0.08

52

98.0

MCC1

0.61

0.22

90

94.1

Sub 2B
Sub3 Swgr

Load

4.16

99.65 -0.4

0.00

0.00

0.40

0.17

0.00

0.00

Sample 3: Load Flow Summary (Undervoltage and Overvoltage Buses)
This section tabulates undervoltage buses and overvoltage buses, indicating the limit violated, the bus ID,
the nominal kV, and the magnitude of the operating voltage in percent of the nominal voltage and in kV.
Undervoltage Buses

-

Critical Limit =

95.00 %, Marginal Limit =

99.00 %

-----------------Bus

Oper. Voltage

Bus

Oper. Voltage

Bus

Oper. Voltage

=====================

===============

=====================

===============

=====================

===============

ID

kV

% Mag.

kV

ID

kV

% Mag.

kV

ID

kV

% Mag.

------------

-------

------

-------

------------

-------

------

-------

------------

-------

------

0.480

98.00

MCC1

Operation Technology, Inc.

kV
-------

0.470#

15-36

ETAP PowerStation 4.0

Load Flow Analysis
Overvoltage Buses

-

Output Reports

Critical Limit =

105.00 %, Marginal Limit =

101.00 %

----------------Bus

Oper. Voltage

Bus

Oper. Voltage

Bus

Oper. Voltage

=====================

===============

=====================

===============

=====================

===============

ID

kV

% Mag.

kV

ID

kV

% Mag.

kV

ID

kV

% Mag.

------------

-------

------

-------

------------

-------

------

-------

------------

-------

------

kV
-------

All bus voltages are below this limit.

Note: * indicates bus voltages violate critical limit.
# indicates bus voltages violate marginal limit.

Sample 4: Load Flow Summary (Branch Loading)
This section identifies branches by giving their IDs, and then indicating the allowable ampacity, loading
current and percent loading for cables, maximum MVA capability, loading MVA, and percent loading of
transformers. Overload cables and transformers are flagged.
Branch Loading Summary Report
----------------------------CKT / Branch

Cable & Reactor

=========================

===========================

Two-Winding

Transformer

====================================================

Loading

Capability

Loading (input)

ANSI Loading(output)

ID

Type

Ampacity

Amp

%

MVA

MVA

%

MVA

%

------------

-----------

--------

-------

--------

----------

--------

--------

---------

---------

T3

Transformer

1.500

0.374

25.0

0.372

24.8

XFMR 3

Transformer

1.500

0.652

43.5

0.641

42.8

T2

Transformer

15.000

3.485

23.2

3.408

22.7

Sample 5: Load Flow Summary (Branch Losses)
This section indicates the branch ID, connected bus IDs, MW, and Mvar flows into each side of the
branch, kW and kvar losses, percentage voltage, and voltage drop for each branch. Losses are calculated
by adding the From-To and To-From bus flows for each branch. Voltage drops, in magnitude, are
calculated by obtaining the difference between the From and To bus voltages. The last column of the
Branch Losses Summary Report sets forth voltage drops across the branches due to different phase
angles.
Branch Losses Summary Report
---------------------------CKT / Branch

Connected Bus Info.

From-To Bus Flow

To-From Bus Flow

Losses

% Bus Voltage

Vd

============

=========================

==================

==================

=================

=============

% drop

ID

From Bus ID

To Bus ID

MW

Mvar

MW

Mvar

--------

--------

--------

--------

Sub 2A

-3.368

-1.356

3.387

1.362

19.0

LVBus

Sub3 Swgr

-0.366

-0.066

0.367

0.075

T2

Main Bus

Sub 2A

-0.689

3.417

0.692

XFMR 3

MCC1

Sub3 Swgr

-0.613

-0.190

Cable2

Sub 3

Sub3 Swgr

1.382

0.467

T1

Sub3 Swgr

Sub 3

------------

------------ ------------

Cable11

Bus3

T3

kW

kvar

From

To

in Vmag

------ ------

-------

6.4

99.74 100.29

0.55

0.5

9.2

99.06

99.65

0.59

-3.337

3.5

79.6

100.00 100.29

0.29

0.614

0.220

1.1

30.8

98.00

99.65

1.65

-1.381

-0.465

1.2

1.3

99.76

99.65

0.11

0.5

18.7

(3 winding transformer)

-------- --------

Sub 2A
-------- -------25.7

Operation Technology, Inc.

15-37

146.0

ETAP PowerStation 4.0

Load Flow Analysis

Output Reports

Sample 6: Load Flow Summary (Generation, Loading, and Demand)
This section summarizes the total generation, loading, and demand, which give totals of MW, Mvar,
MVA, and %PF for the swing bus(es), generators, total demand, and motor loads. MW and Mvar totals
are also given for the static loads, the apparent losses, and the system mismatch. This summary also
indicates the number of iterations it took the program to effect the convergence.
SUMMARY OF TOTAL GENERATION, LOADING & DEMAND
---------------------------------------------

Swing Bus(es):

MW

Mvar

MVA

% PF

=========

=========

=========

==============

-0.531

3.311

3.353

15.8

Leading

6.300

-2.000

6.610

95.3

Leading

97.5

Lagging

Generators:
Total Demand:

5.769
---------

1.311
---------

Total Motor Load:

5.306

1.040

Total Static Load:

0.437

0.125

Apparent Losses:

0.026

0.146

System Mismatch:

0.000

0.001

Number of Iterations =

Operation Technology, Inc.

5.916
--------5.407

-------------98.1

Lagging

171

15-38

ETAP PowerStation 4.0

Load Flow Analysis

Alert View

15.7 Alert View
The Alert View’s functional objective is to provide an immediate list of all the alerts generated by the
Load Flow calculation. The Alert View Window may be configured to automatically display as soon as
the Load Flow calculation is over by selecting the Auto Display check box in the alarm page of the Load
Flow study case. It may also be accessed by a left click on the Alert View Icon. The Alert View provides
several tabulated sections of information about the reported alerts. You may refer to Section 16.2.2 Alert
Page for detailed information on alerts for each type of elements.

Device ID
The Device Identification section of the Alert View lists the names of all the components that qualified as
alerts after the Load Flow calculation.

Type
The type section of the Alert View displays information about the type of the device having the displayed
alert.

Rating
The rating section of the Alert View provides the rating information being used by the load flow program
to determine whether an alert should be reported and of what kind. Section 16.2.2 Alert Page provides
detailed information on alerts for each type of elements.

Calculated
The calculated section of the Alert View displays the results from the Load Flow calculation. The results
listed here are used in combination with those displayed in the ratings section to determine the operating

Operation Technology, Inc.

15-39

ETAP PowerStation 4.0

Load Flow Analysis

Alert View

percent values. These values are then compared to those entered in the Load Flow study case editor alarm
page.

%Value
This section displays the percent operating values calculated based on the Load Flow results and the
different element ratings. The values displayed here are directly compared to the percent of monitored
parameters entered directly into the Alert Page of the Load Flow Study Case Editor. Based on the
element type, system topology and given conditions, the Alert Simulation Program uses these percent
values to determine if and what kind of alert should be displayed.

Condition
The conditions section of the Alert View provides a brief comment about the type of alert being reported.
In the case of Load Flow alerts, the different conditions reported are Overloads, Over Voltage, Under
Voltage, Over Excited, and Under Excited.

Operation Technology, Inc.

15-40

ETAP PowerStation 4.0