CYME
Power Engineering Software
CYME 8.2 - Power Flow Analysis Users Guide
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
Copyright CYME International T&D Inc.
CYME
Power Engineering Software
Contents
Contents
1 – Getting Started ............................................................................................................ 1
2 – Load flow analysis dialog box ................................................................................... 7
3 – Results ....................................................................................................................... 39
Index................................................................................................................................. 51
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Introduction
The objective of a load flow is to analyze the steady-state performance of the power system under
various operating conditions. It is the basic analysis tool for the planning, design and operation of any
electrical power systems. These could be distribution, industrial or transmission networks.
The basic load flow question for a known power system configuration is as follows:
Given:

the load power consumption at all buses

the power production at each generator
Find:

the voltage magnitude and phase angle at each bus

the power flow through each line and transformer
The CYME Power Flow capabilities encompass solution algorithms for balanced and unbalanced
networks. The ones available in the application depend on your license key.
Unbalanced networks:

Voltage Drop

Newton-Raphson (Requires the CYME Distribution Analysis package or the CYME Secondary
Network Grid Analysis Module)
Balanced networks:

Voltage Drop

Fast Decoupled

Full Newton-Raphson

Gauss-Seidel
The Power Flow module operates in conjunction with other add-on modules, namely:
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
The Harmonic Analysis: to communicate the fundamental frequency voltages and currents for
harmonic distortion calculations.

The Stability Analysis: to communicate the initial conditions to the transient stability Analysis
Program.

The Dynamic Motor Start Analysis: to account for system wide voltage drops during motor start.
System parameters
System Frequency
Fundamental network frequency.
Note:
2
You can maintain two equipment databases
(especially for lines and cables), like one for winter and
one for summer for example. The same equipment
ID’s would be used in both databases, but the
impedances would be different for the same equipment
ID. To change between databases easier, and define
for each DB a unique “Database Configuration”. See
Database > Create for details on how to create a
database configuration.
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Base Power
Defines the base for the per-unit impedance of the Substation Equivalent
and for the per-unit Thevenin impedance you can request in the Shortcircuit report. (CYME calculates with ohm values, not per-unit.) With the
DC Load Flow and/or the DC Short-Circuit Analysis optional modules,
you will be able to set the DC Base Power value as well.
Base Voltage
(e.g., 120V, 12,470V) is the voltage to which the base voltage results will
refer to. You may change it anytime.
Earth Resistivity
Influences the zero-sequence parameters. Expressed in Ohm-m.
Earth Return Model
To determine the method used to calculate line impedances and
admittances for overhead lines (balanced and unbalanced), by-phase
lines, double-circuits and unshielded cables. Both models are based on
Carson’s equations.
Infinite & Uniform:
Earth is modeled as an infinite, uniform solid with a flat uniform upper
surface and a constant resistivity. Any end effects introduced at the
neutral grounding points are not large at power frequencies, and are
therefore neglected. This method is valid for low frequency systems.
When using conductor equipment, GMR and diameter are used for
calculation.
Note:
This method can’t be used if the number of conductors
per phase is greater than one. In this case, the complex
plane model will be used.
Complex Plane:
Earth is modeled as a complex ground return plane. The model was
initially proposed by C. Gary to approximate Carson’s infinite series
equation for the whole range of frequencies and for the for multi-layer
ground return. (Reference: C. Gary, "Approche Complète de la Propagation
Multifilaire en Haute Fréquence par Utilisation des Matrices Complexes", EDF
Bulletin de la Direction des Études et Recherches-Série B, No. 3/4, 1976, pp. 520.)
When using conductor equipment, internal and external diameters are
used but not GMR.
Note:
Balanced Line and
Cable Model
If the spacing is defined with GMD, the impedances
will be calculated using the infinite and uniform model.
Two options are available: Nominal PI and Distributed Transposed.
By default, the lines are modeled based on the Nominal PI model.
The Distributed Transposed option applies only to balanced lines and
cables with user-defined impedances that are of equal length or longer
than the threshold specified in the field right below. With this option
selected, the program applies correction factors to the Nominal PI model
in order to calculate the impedances more precisely.
For section length
longer than
With the Distributed Transposed option selected, the program applies
that model to balanced lines or cables of equal length or longer than the
length the user indicates here.
Energy Cost
The energy cost per kWh is used for the calculation of the cost of losses.
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Study preferences
The study preferences are subdivided into categories such as units, user defined simulation text and
parameters. The parameters to look for are at the Units tab, the Text tab and the Simulation tab.
A summary of these parameters is listed below for quick reference. For more information, please see
the CYME Reference manual.
Units parameters
This includes the system of units (Metric or Imperial), electrical and conductor impedance units and load
type.
Text parameters
Phase Text
Labels to be displayed for each of phases A, B and
C.
Loading Limit Text
To enter the label text you want to use to describe
the Equipment Rating values in the dialog boxes.
Capacity Flag Levels
Text
Enter the label texts to describe the equipment
Capacity Flag levels in the various dialog boxes
where they are used.
Network Grouping
and Sorting Levels
To enter the text of the field labels that indicate the
grouping levels of the networks, and to determine
the order into which they will be sorted.
Simulation parameters
Voltage Mismatch
Allowed
To enter the minimum and maximum allowable percentage difference
between the system voltage and the equipment rated voltage before
transmitting a warning.
Access the simulation
Using the Simulation toolbar, select Load Flow from the list of available analyses and then click on the
Run Simulation icon
4
.
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It is also possible to run the Load Flow simulation from the menu Analysis > Load Flow. This will
display the Load Flow Analysis dialog box with the Parameters Tab selected.
The Load Flow Analysis dialog box comprises six tabs that will allow you to set the:

Load Flow analysis Parameters including any Load or Generation Scaling Factors.

The Networks that the Load Flow is to be performed on.

The Controls to include or exclude particular equipment.

The Loading Limits of equipment.

The Voltage Limits for bus and/or customer load voltage violations.

The Output options for reports and One-line Diagram.
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Parameters tab
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Configuration
It is possible to create multiple Load Flow analysis templates, each with different simulation parameters.
The use of these templates eases the study of scenarios since the user only has to choose a
configuration instead of checking and un-checking options. These Load Flow analysis templates are
also available for selection when running other analyses that use the load flow.
To create a Load Flow analysis template, go to the Configuration group box and click on the
icon
to start the creation by giving a name to your new template. Choose the analysis parameters to be
associated with this template and click on
from the Load Flow Analysis dialog box.
To remove a template, select its name in the Configuration combo box list and click on the
rename an existing template, select it and click on the
icon. To
icon.
To restore the calculation parameters to default ones, click on the
of the dialog box.
button at the bottom
Calculation methods options
Method
Select the load flow calculation method from the list of available methods:

Voltage Drop - Balanced / Unbalanced

Fast Decoupled - Balanced

Gauss-Seidel - Balanced

Newton-Raphson - Balanced / Unbalanced
Refer to Calculation options for a detailed description of the load flow methods.
The Newton-Raphson Unbalanced Method requires a valid license of the CYME
Secondary Network Grid Analysis Module.
Convergence parameters
Tolerance
If the mismatch between two successive iterations is within the specified
tolerance, then the load flow will declare convergence of the network.
Depending on the calculation method selected, the tolerance will be
expressed in % voltage deviation (dV) or in MVA power mismatch.
Iterations
Limits the total number of iterations to a pre-defined number. The number of
iterations can be increased if the program does not converge.
As an example, the Fast-Decoupled method will normally converges within
10-20 iterations. The Gauss-Seidel method may require much more
iterations.
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Flat Start
(At Nominal
Conditions)
2 – Load flow analysis dialog box
Check this option to initialize all Voltages to the system nominal voltages
(usually 1.0 p.u.) prior to the first load flow iteration. All Capacitors, Tap
Changers, Regulators and Generators will also be initialized to their initial
states as defined in the network settings.
If you do not check this option, the states and voltages of the previous load
flow will be re-submitted as initial conditions for the load flow calculation.
Remove All
Constraints
If this option is checked then the load flow will be solved by relaxing all the
constraints on Generators (Qmax and Qmin), Load Tap Changing
Transformers and Regulators.
Note:
This is useful for networks that have difficulty converging
since the results of the load flow, with relaxed
constraints, can provide useful tips as to where the
problem may be.
Calculation options
Assume Line
Transposition
When performing an Unbalanced Load Flow, you have the option to
assume or not line transposition in the calculation of the overhead line
impedance matrix. This option has an effect on the calculation only when
the overhead lines are modeled By-Phase with a valid phase position.
Include Line
Charging
To include line charging in the load flow calculation. Usually, for a low
voltage line of short distance, the line charging can be neglected.
Adjust
Impedances
Enable this option to have access to the Impedance Adjustment dialog
box (Edit button), which allows adjusting the conductor resistance according
to temperature, and adjusting transformer impedance and line and cable
length according to tolerances.
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Enable the Include source impedance option to include the equivalent
impedance between the node and the voltage constraint. This option will be
automatically active in the locked rotor analysis where voltage dips may
prevent voltage regulation at substation terminals.
The fault level for the impedance can also be selected.
Enable the Adjust bare overhead conductor at option to adjust the
conductor resistance of overhead lines in the network. The adjustment can
be done according to the operating temperature indicated in the System
Parameters, or can be user-defined.
The conductor resistance is by default at 25C or 50C, or as per set in File
> System Parameters. When the Adjust Conductor Resistance option is
selected, the conductor resistances will be adjusted with the use of the
temperature coefficient of resistance .
𝑅𝑇 = 𝑅𝑟𝑒𝑓 (1 + ∝𝑟𝑒𝑓 (𝑇 − 𝑇𝑟𝑒𝑓 )
For cables, you may select to adjust the conductor resistance using the
Operating Temperature as defined in the cable settings, the Continuous
operating temperature rating as defined the equipment properties or a
User defined temperature.
Enable the Adjust impedances using tolerances checkbox to adjust:
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Transformer impedances with user-defined tolerances or with tolerances as
specified in the IEC 60076 or IEEE C57.12 standard.
Line and cable lengths with user-defined tolerance.
Evaluate State
of Network
Protectors
This option requires the Secondary Network Grid Analysis Module.
Should this option be selected, then the analysis would take into
consideration the fact that Network Protectors would open if backward flow
is detected. Users can set a number of Maximum attempts within which
the analysis will try to find a solution for the final state of the network
protectors for the configuration of the network under study.
Simulation conditions
Ambient
Temperature
Temperature controlled capacitors will be switched on or off based on the
ambient temperature specified here.
Time
Time controlled capacitors will be switched on or off based on the time
specified here.
This parameter may also be used as a simulation starting time for the LongTerm Dynamics analysis.
Load and generation scaling factors
Scaling factors can be globally applied to Loads, Motors and Generators without the need to edit the
network settings. Five different methods are offered to apply the scaling factors:

As Defined

Global

By Zone

By Equipment Type (Load, Generator or Motor)

By Network
By default, the factors will be set to “As Defined” and implies that no scaling factors will be applied to
any of the equipment.
Global factors apply to all Loads, Motors or Generators in the network. The factor for each data entry
field implies that the actual value of (P, Q) as entered in the network settings or database will be
multiplied by the Factor/100%. For the power factor, the values defined in the network settings will be
replaced by the global power factor for the purpose of the simulation.
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By Zone implies that the factors will apply on specified zones of the network.
By default, all factors are set to 100 %. To Edit the default values or to Create a new set of factors, click
on the
icon. For loads, for example, the Load Scaling Factors (by Zone) dialog box with a listing
of all zones defined in the network and the default P and Q values will be displayed on screen.
Click on the
icon to create a new set of user defined scaling factors to be applied on the respective
zones. A dialog will prompt you for a name. Enter the desired name (ex: Light Load).
When creating a new set of factors, you have the option to initialize the values using default values
(Use default values) or to copy existing values from another template (Use values from).
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To delete a user defined set of factors click on the
Qmax) and Motors (P, PF).
icon. The same applies to Generators (P, Qmin,
By Load/Motor/Generator Type implies that the factors will apply on the specified equipments only.
Click on the
icon to edit the factors. For Loads for example, this option multiplies all Active (P) and
Reactive (Q) loads separately based on their customer type assignments. Type in the factors in the
spaces provided. For example: Setting the active load factor (P) = 110 % implies that the load entered
in the Load Properties dialog box will be multiplied by 1.1 (10% increase). Check the option P=Q if you
wish to enter the same values for the active and reactive power.
Any number of templates (set of factors) can be created. For example, a set of factors could represent a
specific period (time of day, season, peak etc) or a specific study mode (Planning, Design, etc). To
select a template, click on the
symbol and select the desired name.
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For Motors, scaling factors can be applied to Induction and Synchronous Motors separately.
For Generators, scaling factors can be applied to synchronous generators, induction generators,
electronically coupled generators, wind energy conversion systems, solid oxide fuel cells, photovoltaic
and micro-turbines. The reactive power generation factors (Qmin and Qmax) will multiply the values
specified in the network settings.
By Network implies that the factors can be different for each network.
By default, all factors are set to 100 %. To Edit the default values or to Create a new set of factors, click
on the
icon. The Load Scaling Factors (by Zone) dialog box lists all networks available with the
default P and Q values for each.
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Click on the
icon to create a new set of user defined scaling factors to be applied per network. A
dialog will prompt you for a name. Enter the desired name (ex: Light Load).
When creating a new set of factors, you have the option to initialize the values using default values
(Use default values) or to copy existing values from another template (Use values from).
To delete a user defined set of factors click on the
icon.
Voltage and frequency sensitivity load model
The Voltage and Frequency Sensitivity Load Model defines how the load will vary with voltage and
at which voltage threshold should they be switched to constant impedance loads to avoid mathematical
convergence problems of the load flow. The following table provides an example of the variation of the
current drawn by a load based on the applied voltage.
Voltage
Constant kVA
Constant Current
Constant Impedance
110%
91%
100%
110%
100%
100%
100%
100%
90%
111%
100%
90%
60%
167%
100%
60%
Example: Current drawn by a load at different voltages.
The relation between the load power and applied voltage can be expressed as:
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𝑛𝑃
𝑉
𝑃 = 𝑃𝑜 × (
)
𝑉𝑏𝑎𝑠𝑒
𝑛𝑄
𝑉
𝑄 = 𝑄𝑜 × (
)
𝑉𝑏𝑎𝑠𝑒
Where:
Po = Nominal Active Power
Qo = Nominal Reactive Power
When the network is heavily loaded and the voltages are lower than nominal as a result, it is
mathematically “easier” to solve the network if the load is mostly of the constant impedance type. In that
case, as the calculated voltage decreases, the load power decreases faster. This means less current
flowing to the load and therefore less voltage drop in the subsequent iteration.
Conversely, if the load is constant power, then the power does not change when the voltage tends to
drop. The current drawn by the load then has to increase, and thus aggravating the voltage drop in the
circuit.
The Voltage Threshold parameter is mainly used as a mathematical parameter helping the
convergence of heavily loaded systems by converting all loads where the voltage falls below the
specified limit to constant impedance. To avoid unexpected conversions of load models during the
simulation, it is recommended to set (Vz) to a low value (<=80%).
Five options are offered to define the voltage sensitivity load models: As Defined, Global, By Zone, By
Load Type or By Network
As Defined is the mode selected by default. In this mode, the sensitivity factors and voltage thresholds
are automatically selected from the default Customer Type Library.
As Defined implies that the sensitivity model is customizable per load type and the load model can be
selected from three load model types:

Composite (ZIP) model

Exponent model

Mixed: ZIP and Exponent model
Click on the
icon to view or modify the default values of the customer type library. The Customer
Type Library is part of the network settings. For more information on creating new Customer Types
and/or editing the default library values, refer to chapters on Network Types and Customer Types
(Network menu) in the CYME Reference Manual.
Global allows applying the same exponent sensitivity factors (nP, nQ) and voltage threshold (Vz) to all
loads in the network. The exponent sensitivity factors must be specified in p.u. and the voltage
threshold in %.
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By Zone implies that the exponent factors and voltage threshold will apply to all the loads of the
selected zones.
To “Edit” the default values or “Create” a new set of factors click on the
Note:
icon.
If you have the optional Transient Stability Analysis module, additional entries will be
available in this group box to specify the Frequency Sensitivity factors. Refer to the Transient
Analysis User Guide for further information.
By Network implies that the factors can be different for each network.
To Edit the default values or to Create a new set of factors, click on the
icon. The Voltage
Sensitivity Load Model (by Zone) dialog box lists all networks available with the default P and Q
values for each.
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Click on the
icon to create a new set of user defined scaling factors to be applied per network. A
dialog will prompt you for a name. Enter the desired name (ex: Light Load).
When creating a new set of factors, you have the option to initialize the values using default values
(Use default values) or to copy existing values from another template (Use values from).
To delete a user defined set of factors, click on the
icon.
By Load Type implies that the sensitivity exponent factors and voltage threshold will apply by
categories of customer types. This mode allows the creation of user defined templates of load models
without modifying the default values found in the Customer Type Library.
When a new voltage sensitivity load model is created, it is possible to choose the load model type (ZIP,
exponent or mixed) to be used.
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Composite (ZIP) model
For composite loads, the Load Flow analysis will compute the average values for nP and nQ and apply
them to the load.
Where:

Vz: Voltage Threshold in %

Z:
Constant Impedance %

I:
Constant Current %

P:
Constant Power %
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The values entered for the constant impedance (Z), constant current (I), and constant power (P) must
add up to 100 %.
Note:
For the Fast Decoupled, the Gauss-Seidel and the Newton-Raphson balanced calculation
methods, the ZIP model will be converted to an equivalent Exponent Model during the
simulation using an average value of the weighted sum given by the following:
𝑛𝑃 =
∑𝑖 𝑃𝑖 (𝑛𝑃𝑖 )
∑𝑖 𝑃𝑖
𝑛𝑄 =
∑𝑖 𝑄𝑖 (𝑛𝑄𝑖 )
∑ 𝑖 𝑄𝑖
Where:

Pi and Qi are the % of active and reactive power component of the load.

nPi and nQi are the nP and nQ exponents assigned to each component of the load.

∑Pi and ∑Qi are both equal to 100 %. (The sum of all load types cannot exceed 100 %.)
As an example, the following composite load model was created:
Then the average nP or nQ value are computed as follows:
nP or nQ = (50 % x 0.0) + (30 % x 1) + (20 % x 2) = 0 + 0.3 + 0.4 = 0.70
100%
Those values will be used in the Load Flow Analysis for the calculation methods mentioned
above.
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Exponent model
Where:

Vz: Voltage Threshold in %

nP: Active Power Exponent factor in p.u.

nQ: Reactive Power Exponent factor in p.u.
Note:

nP or nQ = 0.0 means constant-power load

nP or nQ = 1.0 means constant-current load

nP or nQ = 2.0 means constant-impedance load
Mixed: ZIP and Exponent model
The choices of ZIP model and Exponent model are available for every customer type, so the user can
choose any of the two types for each customer type.
Creating a new voltage sensitivity load model template
The explanation below is valid if the load model is By Load Type or By Zone.
To create a new Voltage Sensitivity Load Model, click on the
icon to create a new set of user
defined voltage sensitivity and threshold factors. The following dialog will be displayed:
Name
Enter the name for the particular Voltage Sensitivity Load Model.
Type
Select the Voltage Sensitivity Load Model Type: Zip, Exponent or Mixed.
Blank
Initialize all data entry fields as blank.
From
Copy the values from another voltage sensitivity load model
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From Default
Values
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Copy the values from the default Customer Type Library
Calculation methods
Voltage drop calculation technique
The Load Flow analysis of a radial distribution feeder requires an iterative technique that is specifically
designed and optimized for radial or weakly meshed systems. The Voltage Drop Analysis method
includes a full three phase unbalanced algorithm that computes phase voltages (VA, VB and VC),
power flows and currents including the neutral current.
The calculation returns the results when no calculated voltage on any section of the selected networks
changes from one iteration to the next by more than the Calculation tolerance. Example: |34465.2 –
34464.8|/34464.8 < 0.1%.
However, in some cases, the calculation may not converge to a solution which could either be due to
bad data such as a very high impedance line or could be due to peculiar network configuration.
If during the calculation process the voltage on a section falls below the specified Voltage Threshold,
then for the next iteration, all loads on that section will be converted to constant impedances.
Converting the load in this way does not affect the load data permanently. It is only a way to assist the
calculation to converge to a “solution”, instead of not giving any result at all.
You can use this (artificial) solution to identify problem areas or sections with bad input data, by looking
for section(s) with very low voltage. To avoid using this function, set the voltage threshold to a low
value, such as <=80%. Setting the level higher than 90% is not recommended, for fear of distorting an
otherwise valid solution.
When you select to run a Balanced Voltage Drop the calculation will be performed with the load on
every section assumed to be distributed equally among all the available phases. This will not change
the load data that you have entered through the Section Properties dialog box.
Newton-Raphson unbalanced
The radial structure of distribution systems, the high X/R ratio and the large number of components are
the classical arguments for choosing the utilization of the Voltage Drop based on Backward/Forward
Sweep (BFS) methods to solve the distribution load flow problem. However, new complex systems are
being modeled and have different configurations causing the failure of the traditional algorithms. Such
systems include underground secondary networks (urban grid systems or spot networks), low voltage
installations, and sub-transmission systems tied to the distribution systems. This has transformed the
homogeneous distribution system into a heterogeneous complex system.
The Newton-Raphson Unbalanced is a general, efficient and comprehensive load flow analysis
algorithm exploiting the modified augmented nodal analysis approach (MANA). The design is principally
oriented to solve complex electrical power systems and underground secondary networks (urban grid
systems or spot networks). However, the proposed method is also applicable to balanced, unbalanced,
radial and highly meshed secondary networks, industrial and transmission systems.
The Newton-Raphson Unbalanced method of solving the power-flow problem is an iterative algorithm
for solving a set of simultaneous non-linear equations and an equal number of unknowns based on the
Taylor’s series expansion for a function of two or more variables. The main difference between this
method and the traditional Newton-Raphson Balanced method is that the Newton-Raphson Unbalanced
is based on multi-phase real value coordinates instead of symmetrical components per-unit values,
hence capable of handling more complex systems.
The main equation used by the Newton method is defined by:
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𝐽𝑘 ∙ ∆𝑥 𝑘 = −𝑓 𝑘
Where:

J : Jacobian matrix at iteration k.

f : Mismatch vector at iteration k.

∆x : The correction vector at iteration k.
k
k
k
For complex system analysis, the main system of equations is built using the abridged MANA
formulation below:
𝑌𝑛
𝑉𝑎𝑑𝑗
𝐷𝑏𝑑𝑒𝑝𝑟
[ 𝑆𝑎𝑑𝑗
𝑡
𝑉𝑎𝑑𝑗
0
0
0
𝐷𝑏𝑑𝑒𝑝𝑐
0
0
0
𝑡
𝑆𝑎𝑑𝑗
0
0
𝑆𝑧 ]
𝑉𝑛
𝐼𝑛
𝐼𝑉𝑠
𝑉
= [ 𝑠]
𝐼𝑉𝑑
0
0
[𝐼𝑆𝑊 ]
Where:

Yn : Linear network admittance.

Vadj : Voltage source adjacency matrix, for all voltage source types.

Dbdepr : Branch dependent relations (e.g. transformers).

Dbdepc : Branch dependent relations (e.g. transformers).

Sadj : Adjacency matrix of closed switch type devices.

Sz : Diagonal and unitary matrix for open switch type devices.

Vn : Vector of unknown node voltages.

IVs : Vector of unknown voltage source currents.

IVd : Vector of unknown currents in dependent voltage source branches.

ISW : Vector of unknown switch currents.

In : Vector of known nodal current injections.

Vs : Vector of known voltages.
For the load flow solution, multiphase constraints are added to the simplified MANA formulation. The
Jacobian is obtained by deriving the MANA sub-matrices and traditional methodology is used to solve
the Newton-Raphson iterative algorithm.
Note:
The Newton-Raphson Unbalanced method is available with the CYME Secondary Network
Grid Analysis Module.
Gauss-Seidel balanced
Transmission network power flow analysis techniques are specifically designed for balanced three
phase systems and may exhibit poor convergence characteristics when applied to radial distribution
type feeders.
The set of system equations are typically non-linear, and solving them does require the use of iterative
algorithms.
In order to illustrate the remaining three solution algorithms, we will use the following simple 3-Bus DC
System.
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2 – Load flow analysis dialog box
3-Bus DC System
The impedance matrix equation for the three bus system can be expressed as:
𝑦11
𝑖1
[𝑖2 ] = [𝑦21
𝑦31
𝑖3
𝑦12
𝑦22
𝑦32
𝑦13 𝑣1
𝑦23 ] [𝑣2 ]
𝑦33 𝑣3
The bus voltage equations for Bus V2 and V3 can be expressed as a function of the active power,
admittance and system voltages as follows:
𝑣2 =
1 𝑝2
[ − (𝑦21 𝑣1 + 𝑦23 𝑣3 )]
𝑦22 𝑣2
𝑣3 =
1 −𝑝3
[
− (𝑦31 𝑣1 + 𝑦32 𝑣2 )]
𝑦33 𝑣3
Since these
are nonlinear
equations
then an
iterative
technique
must be
adopted
with an
initial guess
for the
voltages
(Flat Start)
of 1.0 p.u as
illustrated in
the following
flow chart
for the
GaussSeidel
algorithm:
24
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Hint:
2 – Load flow analysis dialog box
The Gauss-Seidel method may offer better chances for convergence in networks with
significant resistance in them. (Branches with X/R < 1.0). Note that this method normally
requires a greater number of iterations to converge to the solution than the other solution
methods.
Newton-Raphson balanced
The Newton-Raphson method of solving the power-flow problem is an iterative algorithm for solving a
set of simultaneous non-linear equations and an equal number of unknowns based on the Taylor’s
series expansion for a function of two or more variables.
The power equations at each bus will be as follows:
𝑝1 = 𝑣1 (𝑦11 𝑣1 + 𝑦12 𝑣2 + 𝑦13 𝑣3 )
𝑝2 = 𝑣2 (𝑦21 𝑣1 + 𝑦22 𝑣2 + 𝑦23 𝑣3 )
𝑝3 = 𝑣3 (𝑦31 𝑣1 + 𝑦32 𝑣2 + 𝑦33 𝑣3 )
The derivative term is a follows:
𝜕𝑝2
∆𝑝2
𝜕𝑣2
[
]=
∆𝑝3
𝜕𝑝3
[𝜕𝑣2
𝜕𝑝2
𝜕𝑣3 ∆𝑣2
[
]
𝜕𝑝3 ∆𝑣3
𝜕𝑣3 ]
The power derivative terms work out to be as follows:
𝜕𝑝2
= 𝑦21 𝑣1 + 2𝑦22 𝑣2 + 𝑦23 𝑣3
𝜕𝑣2
𝜕𝑝2
= 𝑦23 𝑣2
𝜕𝑣3
𝜕𝑝3
= 𝑦32 𝑣3
𝜕𝑣2
𝜕𝑝3
= 𝑦31 𝑣1 + 2𝑦32 𝑣2 + 𝑦33 𝑣3
𝜕𝑣3
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Since these are non-linear
equations then an iterative
technique must be adopted with
an initial guess for the voltages
(Flat Start) of 1.0 p.u as illustrated
in this flow chart for the NewtonRaphson algorithm:
Fast-Decoupled balanced
The Full Newton-Raphson method is formulated as:
𝜕𝑃
∆𝑃
[ ] = [ 𝜕𝛿
∆𝑄
𝜕𝑄
𝜕𝛿
𝜕𝑃
𝜕𝑉 ] [ ∆𝛿 ]
𝜕𝑄 ∆𝑉
𝜕𝑉
Where:

P is the Real Active Power

Q is the Imaginary Reactive Power

V is the Line Voltage

δ is the Voltage Angle
The Decoupled Power-Flow method is a variation of the full Newton-Raphson method and is based on
the fact that a change in the voltage angle at a bus will mainly affect the real power flow in the overhead
line or cable and does not affect the reactive power flow.
Similarly, a change in the voltage magnitude will have a direct impact on the reactive power flow and
does affect the active power flow.
With this in mind the following derivative terms can be approximately set to zero.
𝜕𝑃
𝜕𝑉
26
≅ 0,
𝜕𝑄
≅0
𝜕𝛿
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2 – Load flow analysis dialog box
The active and reactive power derivative terms can be approximated by the following simplified
equations:
[∆𝑃] = [
𝜕𝑃
] [∆𝛿],
𝜕𝛿
𝜕𝑄
[∆𝑄] = [ ] [∆𝑉]
𝜕𝑉
The iterative technique of the Fast-Decoupled method is the same as the Newton-Raphson method.
Networks tab
Select in the list the networks to be analyzed. Click on the check box next to a network name to select
or de-select it individually. Click on the
symbol to expand the list and on
to collapse it again. All
selects every feeder loaded in the study. None de-selects all feeders.
Note:
The Load Flow analysis can simultaneously solve multiple networks and networks with multiple
swing buses.
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Controls tab
The modifications made in this dialog do not permanently change the status of capacitors, regulators,
transformers, generators and motors as defined in the network settings. Instead, it simply allows you
take them in and out of service for a particular analysis.
Include group box
If the check box next to the item is unchecked then the devices of
that type are ignored (Off) for the analysis as they are considered
temporarily disconnected, even if their individual status indicates
that they are in service.
Lock switched
capacitors at their
current state
If this item is checked, the state of shunt capacitors with capacitor
controls will be locked during the load flow. This can be used to
keep the state of a previous load flow.
Lock multi-stage
switchable shunts at
their current state
If this item is checked, the shunt banks that are initially on in multistage switchable shunts will be locked during the load flow.
Transformer tap operation
Normal Tap
Operation
28
The Normal Tap Operation setting uses the taps as defined in the Network
Settings.
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Infinite Taps
2 – Load flow analysis dialog box
The Infinite Tap option does not consider any step; the regulated voltage
will then be exactly the desired voltage.
Hint:
During the planning stage, you can select Infinite Taps to
ensure you get the exact desired voltage.
Lock Taps at
their Specified
Positions
If this option is checked then the load flow is solved by fixing the tap
position of all Load Tap Changing Transformers to the initial tap position
as defined in the network settings.
Disable Tap
Changer
This option has the same effect as setting the tap changer to its neutral
position (no voltage adjustment).
Regulator tap operation
Normal Tap
Operation
The Normal Tap Operation setting uses the taps as defined in the Network
Settings.
Normal Tap
Operation –
Lowest Tap in
Range
This option ensures that the final tap position will be the lowest tap position
required to maintain the voltage above the minimum range of set voltage
bandwidth.
Normal Tap
Operation –
Highest Tap in
Range
This option ensures that the final tap position will be the highest tap
position required to maintain the voltage at the maximum range of set
voltage bandwidth.
Infinite Taps
The Infinite Tap option does not consider any step; the regulated voltage
will then be exactly the desired voltage.
Hint:
During the planning stage, you can select Infinite Taps to
ensure you get the exact desired voltage.
Lock Taps at
their Specified
Positions
If this option is checked then the load flow is solved by fixing the tap
position of all Regulators to the initial tap position as defined in the network
settings.
Disable Tap
Changer
This option has the same effect as setting the tap changer to its neutral
position (no voltage adjustment).
Disable
Regulators with
Python Scripts
Check this option to disable the tap operation of all regulators defined with
a Python script control.
DC Links
If the check box next to the item is unchecked then the DC Links are ignored (Off) for the analysis as
they are considered temporarily disconnected, even if their individual status indicates that they are in
service.
DC Systems
To include the results of the DC systems in the Load Flow analysis output. A valid license of the DC
Load Flow module is required for that option to be available. Refer to the DC Load Flow Analysis Users
Guide for more details.
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Loading limits tab
In this dialog box you can specify the thresholds for equipment overloading condition by choosing the
equipment loading limits as specified in the equipment database, and/or by applying a limit category
factor.
Equipment
Ratings
30
Choose to use one of the five Equipment Ratings. “Nominal” is set in the
Equipment database.
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2 – Load flow analysis dialog box
The text that describes the Equipment Rating values in the dialog box can be
changed in the menu File > Preferences, under the Text tab.
Protective
Device
Rating
Select the protective device rating criteria to use to calculate the protective
device loadings. Choose from Use Equipment Ratings, Nominal Pickup or
Individual Settings.
Limit
Categories
In addition to the Equipment Ratings selected, you may also choose to apply a
loading limit factor. Define a separate capacity level as a percentage to the
selected Equipment Rating. Five operating conditions can be defined, such as
Nominal, Emergency, and Planning.
Choose one of the limit categories and check the option Apply Loading
Limits Factors. If this optional loading limit factors are to be applied, the
selected one would be displayed in blue.
The terms “Nominal”, “Planning” and “Emergency” can be changed in the
menu File > Preferences under the Text tab. Enter the label texts to describe
the equipment Capacity Flag Levels in the various dialog boxes where they
are used.
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Voltage limits tab
In this dialog box you can specify the thresholds for abnormal voltage conditions (low- and high-voltage)
by specifying the system voltage limits, and/or by applying a limit by customer types available.
Limit
Categories
32
This field is linked to the one displayed in the Loading Limits Tab. The chosen
limit category is highlighted in blue in the System Voltage Limit table and in the
Customer Load Voltage Limits table.
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System
Voltage
Limits
2 – Load flow analysis dialog box
For each operating condition, the Over and Under Voltage limits to be used to
report any network component that violates these limits can be specified.
These values are only criteria for evaluating whether a component is
experiencing over or under voltage conditions. They do not affect the
calculation.
The System Voltage Limits can be set to Global limits or By voltage range.
The Global Limits category applies the specified over-voltage and undervoltage limits to all components of the networks. The By voltage range
category allows the definition of over-voltage and under-voltage limits for
different voltage ranges.
To define a voltage range, click on the
Edit Voltage Ranges dialog box.
Customer
Loads
Voltage
Limits
button to access the
Enable the Apply voltage limits by customer types if voltage limits are
desired per customer type available in the networks.
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2 – Load flow analysis dialog box
Output tab
Different output options are available upon the completion of the load flow analysis. These options
would allow the automatic generation of the reports selected and the display of results on the one-line
diagram.
Display the
Iterations Report
To display the load flow iteration report. Refer to section Solving the load
flow for further details.
This is a useful option if no solution is found, since you will be able to
inspect the Iteration Report to try to identify the portion of the network
that may be causing the problem. If this is the only time when an Iteration
Report is desired, enable the option Only on non-convergence.
Choose the option Use same iterations report to refresh the existing
iteration report instead of creating a new one at the end of every
simulation.
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Display the
Summary Status
Dialog Box
2 – Load flow analysis dialog box
To display the status box showing the parameter settings used and
indicating whether any abnormal conditions were encountered (overload,
low-voltage, and high-voltage).
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Check the Select checkbox to enable report display. Use the
button in the Reports grid to select
the reports to be displayed, and use the drop-down menu to select the appropriate result tags, color
coding and/or tool tips configuration to be displayed.
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Solving the load flow
Once the parameters for the load flow analysis have been set, clicking on the Save button will save the
parameters to the calculation configuration file in a permanent manner. This is only useful if the same
parameters are re-used as default parameters for future studies.
Click on the Run button to start the analysis. Depending on the calculation method selected, the
following iteration reports will be displayed (if the option Display Iteration Report is checked).
If the calculation tolerance is expressed in % voltage deviation, the following iteration report will be
displayed.
At each iteration, the load flow computes the voltage at every section in the network. It compares the
new values with the values it calculated from the previous iteration and reports the section where the
voltage has changed the most (Max dV in %). The process continues until the solution is found or until
the maximum number of iterations is reached.
Any adjustment/status change for tap changers, generators and shunt capacitors are also listed for
each iteration.
If the calculation tolerance is expressed in MVA power mismatch, the following iteration report will be
displayed.
Hints:

By inspecting this report, it is possible to determine whether devices are continually being
adjusted.

If so, try changing the settings of one or more of them before solving again.
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3 – Results
3 – Results
Reports
To select and display the load flow reports click on the
Report > On Calculation from the menu.
icon of the Simulation toolbar or select
Here are a few samples of reports that can be selected.
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Sample Load Flow Summary Report
Notes on the Load Flow Summary report:
1.
2.
40
Differences between Load Read (non-adjusted) and Load Used (adjusted):
a)
Load Read: Total load connected to the network, i.e., the sum of each individual load point.
b)
Load Used: Total load used for the Load Flow analysis. This value may be different from the
load as it is influenced by the load scaling factors, the voltage sensitivity load model and the
constant impedance voltage threshold.
Annual Cost of System Losses: CYME first annualizes the kW losses calculated through the Load
Flow analysis considering the load factor defined for each network (Edit > Add Network >
Demand tab, Annual Losses group box). Then, the Cost of energy defined under File > System
Parameters is used to calculate the total annual cost.
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Sample Load Flow Feeder Loading Report
Sample Load Flow Detailed Report
See the Report Menu chapter in the CYME Reference Manual to learn about the various commands
available to use the predefined report forms and/or to generate sophisticated user defined reports
particularly through the use of XSL template.
Report by individual section
To see the report by individual section, first enable the “Voltage Drop Box” via View > Result Box >
Load Flow Box. Then click on a section on the one-line display. For more information regarding result
boxes, please refer to the CYME Reference Manual.
Hint:
Use the keyboard shortcut <Alt> + <V> to hide or show the Load Flow Box.
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The description of the default data reported in the Load Flow Box is detailed below. Note that the
contents of the Load Flow Box can be customized. Refer to the Customize (Result boxes) chapter in
the CYME Reference Manual.
V base
Voltage referred to the base voltage defined in File > System Parameters
dialog box.
𝑣=
𝐴𝑐𝑡𝑢𝑎𝑙 𝑉
𝑥 𝐵𝑎𝑠𝑒
𝑁𝑜𝑚𝑖𝑛𝑎𝑙 𝑉
kVLL
Line-to-line voltage at the secondary side, expressed in kV.
KVLN
Line-to-neutral voltage at the secondary side, expressed in kV.
i (A)
Phase current in Amperes into the sub-section.
kVA
Apparent power flowing into the sub-section.
kW
Real power flowing into the sub-section.
kVAR
Reactive power flowing into the sub-section.
Choice of measurement location. See diagram below, and recall from
Section Structure that there may be three sub-sections in a section.
One or two of the circles will not be active if no equipment is connected,
which would divide the section into sub-sections.
The three locations for measuring the current, power and voltage:
Displays the Chart Selection dialog box.
Exports the information table data to Microsoft Excel and opens the Excel
application with the data laid out in a spreadsheet.
Copies the content of the result grid onto the Clipboard to facilitate pasting
the contents into a document.
Allows the duplication of any number of result boxes.
Allows the selection of results to appear in the result box.
Disable the updates of the results for this result box.
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This option allows switching between the Default Result Box layout and the
Custom Result Box layout. A custom layout is a layout defined for a specific
device. The default layout applies to all devices. See the CYME Reference
Manual for more information.
Click on this button to decrease the number of decimals displayed in the Load
Flow Box.
Click on this button to increase the number of decimals displayed in the Load
Flow Box.
Allows holding the results displayed in the result box for the currently selected
location on the one-line diagram.
Click on this icon to zoom and center the monitored item in the display.
Please refer to the View menu chapter and the Customize menu of the CYME Reference Manual for
further details on the Result Box options.
Hint:
Colors in the Load Flow Results Box.
Colors in the result box identify overloads and under/over-voltage conditions according to the
Loading Limits thresholds given via Analysis > Load Flow, Voltage/Loading Limits tab.
The alarm colors (as defined in the Abnormal conditions color coding) appear in the result box
even if the one-line color-coding feature has been turned (View > Display Options; click on the
Modify button in the Symbols group box to display the Symbols – Default symbols dialog
box, and go to the Abnormal Conditions tree item in the list.)
Hint:
Negative values will appear if the power is flowing from the load end toward the source end,
since flow (current and power) is defined as positive the other way.
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Charts
The icon
inside the Load Flow Box and in the Simulation Toolbar allows you to display the Chart
Selector dialog box where you can select the charts to plot (Voltage profile, kVA profile, kVAR profile,
etc.) along the network, from the substation to the node of the active section.
Apply on allows the user to plot simulation results of feeders from a selected node (traced to the
source) or a single network or all networks.
The Enable Filter option allows narrowing down the results tracing based on user-defined filters. See
the Customize > Filters chapter in the CYME Reference Manual for more information.
Select the desired charts from the list and click on Display to view the charts.
Plot of Voltage Profile
It is possible to print the selected chart once it is plotted via the File > Print menu command.
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Note that the Load Flow Results Box (if displayed) will be superimposed on the plot. You may hide it
temporarily by closing its window. (Press <Alt> + <V> to get it back again.)
Hint:
If any changes are made to the network, such as adding a load, the application will discard all
of the analysis results, and the results box will disappear.
The customization of the charts may be done through the menu Customize > Charts (or by clicking on
the Customize button in the Chart Selector dialog box). Refer to the Customize (Charts) chapter in the
CYME Reference Manual.
One-line diagram tags
Load flow results may be displayed on the One Line Diagram (See the example below). The tag layers
can be selected and configured using the Tag Layer toolbar. It can be useful to create and completely
customize your own layer of result tags; to do so, use the Customize > One-Line Diagram > Tags and
Text menu command. Consult the CYME Reference Manual for more information.
One-Line Diagram Report Tags
Hint:
The Tool Tip can also be used to display the Tag contents. Hovering the mouse over a section
will display the tool tip. The contents of the tool tip can be modified. To do so, go to the Tool tips
group box of the View > Display Options dialog box.
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One-line diagram color coding
The one-line diagram can be color-coded based on the load flow results. It is possible to select from a
list of predefined coloring layers or create customized color coding layers. The active color coding layer
is selected using the Color Coding Layer toolbar. Creating and customizing color coding layer is done
with the Customize > One-Line Diagram > Color coding menu command. Consult the CYME
Reference Manual for more information.
Refer to the Display Options chapter in the CYME Reference Manual to learn how to customize and
create new one-line diagram color coding layer.
The abnormal conditions are displayed on the one-line diagram by clicking on the
analysis toolbar.
icon of the
.
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Convergence issues
Some networks may exhibit difficulty in converging or do not converge at all. This chapter provides
some hints as to what to look for.
Voltage drop and Newton-Raphson unbalanced methods
When the Voltage Drop and the Newton-Raphson Unbalanced calculation methods fail to converge,
the following recommended steps should help you find the potential causes of the non-convergence.
1.
Enable the option Display Iterations Report in the Load flow Output tab.
2.
Try relaxing the constraints on the devices by enabling the option Remove All Constraints in the
Load flow parameters tab. If the Load flow converges, investigate the setting adjustments of
regulators, LTCs and generators.
3.
Try reducing the load factor until the load flow converges. For example, try a load factor of 70%
(global load factor =70%) and continue to reduce the load factor until the Load flow does converge.
Once a solution is found, identify the areas with low voltages and investigate those areas for
potentially large loads or large impedances.
4.
If the Max dV is increasing steadily in the iteration report, check the input data for components
connected to the indicated section. Look for very high impedance.
Hints:

Check that transformer voltages are entered in kV, not Volts. For example, 480 V is 0.48
kV, not 480 kV.

Make sure line and cable lengths are consistent with the unit of length specified. For
example 15000 ft. is 2.84 mi, not 15000 mi.
5.
If the Max dV steadily decreases in the iteration report but remains higher than the specified
solution tolerance when the permitted number of iterations is exhausted, try increasing the number
of iterations before solving again. See Analysis > Load Flow, Parameters tab.
6.
If the Max dV becomes large and repeatedly increases and then decreases in the iteration
report, look for a very high load downstream supplied through a large impedance.
7.
Verify the settings of switched capacitors, regulators, LTC transformers, and generators. Make sure
that the control settings are adequate.
Hint:
A Cancel button allows you to cancel the calculation before all of the permitted iterations are
performed, in case the calculation is not converging. Use it to save some time.
Gauss-Seidel, Fast Decoupled and Newton-Raphson balanced methods
For these methods, the following recommended steps should help find the potential causes of the nonconvergence.
1.
If the Max dQ increases steadily, check the input data for equipment connected to the buses
indicated. Check the data of all branches connected to the bus and in particular the impedance of
the branch. A very high or very low branch impedance may be the cause of the problem.
Hint:
Ensure that transformer impedances are entered correctly in p.u. (0.075) or percent (7.5).
Make sure that line and cable lengths are consistent with the length unit used for defining the
impedance. (e.g., 200 m is 0.200 km).
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2.
If the Max dQ increases and decreases and devices are being adjusted at every iteration, try and
solve without constraints. If the calculation converges, try to identify from the results where the
problem comes from. (Example: excessive VAR requirements).
Hint:
Perhaps two devices have been set to control the voltage at the same bus.
3.
If the Fast-Decoupled or Newton-Raphson method does not converge even when the constraints
are deactivated, try the Gauss-Seidel method. Allow more iterations for this method.
4.
If the Max dQ steadily decreases but remains higher than the specified solution tolerance when
the permitted number of iterations is exhausted, try increasing the number of iterations before
solving again, or de-activate the "flat start" option in the Convergence parameters group box of the
Parameters Tab dialog box and solve again immediately.
5.
If the Max dQ repeatedly decreases and then increases suddenly, the solution (if it exists) may
be near an unstable point. Try to approach the case under study by successively modifying a
similar case, which has a solution.
Networks with abnormal voltages
This section provides some basic hints in trying to solve power flows in which very high or low bus
voltages are expected.
Some Power Flow solutions (whether realistic or not) require that bus voltages attain very high ( > 1.10
p.u.) or very low (< 0.80 p.u.) values in order for the calculation to converge.
Examples:

Small islanded generators, such as emergency generators, with heavy loads.

Industrial systems operation without connection to a utility grid.

Small utilities serving light loads connected to long transmission lines.
Here is a helpful technique, which can be applied to each of these cases:
1.
If there is only one generator in a heavily loaded network, and the operation simulated is at low
voltages, set the desired voltage of the generator bus to a value near what you expect it to be (e.g.,
0.85 p.u.). A lone generator must operate as a swing machine (hence it has unlimited power
capability), but if the solution shows that its MW and MVAR production are within the limits of the
real machine, then the solution is a valid one. There are, however, many valid solutions.
2.
Use trial and error with the Operating kV to try to get the generator to produce its maximum
reactive power, Qmax. That should result in the highest possible voltages.
3.
If trying to estimate how much load an islanded generator can carry, use the same technique,
and run successive power flows, each time gradually adding more load, until the generator output
reaches the limits of the real machine.
4.
If there is more than one generator, apply the same technique. One generator operates as a
swing machine, of course. If necessary, adjust the settings of the other generator(s) to make the
Qmin and Qmax artificially very large (make Qmin =  Qmax). If the solution shows the MVAR output
to be within the realistic limits of the generator, then the solution is a valid one. [The idea is to give
the calculation freedom to iterate toward the unusual solution.]
5.
48
If long unloaded transmission lines are contributing many MVAR into the network, such that
the voltages are expected to attain very high values, apply the same technique, and set the
Operating kV of the generator’s bus to a value near what you expect (e.g., 1.20 p.u.). (There are,
however, many valid solutions.)
CYME 8.2 - Power Flow Analysis - Users Guide
CYME
Power Engineering Software
6.
3 – Results
Use trial and error with the Operating kV to try to get the generator to produce (or absorb) its
minimum reactive power, Qmin. That should result in the lowest possible voltages.
Parallel operation of generators
This applies to more than one generator connected to a bus. The generators do not have to be the
same type. This note describes the power sharing among generators connected to the same bus.

Fixed generators are treated as constant (negative) MW and MVAR load. Fixed generation does
not affect what follows.

Swing generators share the required active and reactive generation equally, regardless of their
nominal MVA rating.

Voltage-controlled generators each produce their specified active generation (Pgen). Their share of
the reactive power required in the solution (Qgen) is computed as follows:
𝑞 = 𝑞𝑚𝑖𝑛 +
𝑄𝑔𝑒𝑛 − 𝑄𝑚𝑖𝑛
𝑥 (𝑞𝑚𝑎𝑥 − 𝑞𝑚𝑖𝑛)
𝑄𝑚𝑎𝑥 − 𝑄𝑚𝑖𝑛
Where:

qmin and qmax are the reactive limits of the particular generator.

Qmin and Qmax are the sums of the qmin's and qmax's of the voltage controlled generators
connected to the bus.

Qgen is the required reactive generation at the bus.
If Swing and Voltage-controlled generators are connected to the same bus, then each V-C generator
produces its specified active generation, and the swing generators share the excess.
In that case, the reactive power allocated to each voltage-controlled generator is calculated differently.
If Qgen exceeds Qmax, each voltage-controlled generator generates its Qmax, or If Qgen is less than
Qmin, each voltage controlled generator generates its Qmin. In either case, the swing generators
share the excess.
CYME 8.2 - Power Flow Analysis - Users Guide
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CYME
Power Engineering Software
Index
Parallel operation of generators................................... 49
Parameters tab .............................................................. 7
Index
Report by individual section ......................................... 41
Reports ........................................................................ 39
Results ........................................................................ 39
Simulation conditions ................................................... 11
Access the simulation ................................................... 4
Simulation parameters ................................................... 4
Calculation methods.................................................... 22
Solving the load flow.................................................... 37
Calculation methods options ......................................... 8
Study preferences ......................................................... 4
Calculation options ........................................................ 9
System parameters ....................................................... 2
Charts ......................................................................... 44
Text parameters ............................................................ 4
Composite (ZIP) model ............................................... 19
Units parameters ........................................................... 4
Configuration ................................................................. 8
Voltage and frequency sensitivity load model .............. 15
Controls tab ................................................................. 28
Convergence issues.................................................... 47
Voltage drop and Newton-Raphson unbalanced
methods ................................................................... 47
Convergence parameters .............................................. 8
Voltage drop calculation technique .............................. 22
Creating a new voltage sensitivity load model
template .................................................................. 21
Voltage limits tab ......................................................... 32
Exponent model .......................................................... 21
Fast-Decoupled balanced ........................................... 26
Gauss-Seidel balanced ............................................... 23
Gauss-Seidel, Fast Decoupled and NewtonRaphson balanced methods ................................... 47
Getting Started .............................................................. 1
Introduction ................................................................... 1
Load and generation scaling factors ........................... 11
Load flow analysis dialog box ....................................... 7
Loading limits tab ........................................................ 30
Mixed
ZIP and Exponent model ......................................... 21
Networks tab ............................................................... 27
Networks with abnormal voltages................................ 48
Newton-Raphson balanced ......................................... 25
Newton-Raphson unbalanced ..................................... 22
One-line diagram color coding .................................... 46
One-line diagram tags ................................................. 45
Output tab ................................................................... 34
CYME 8.2 - Power Flow Analysis - Users Guide
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