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Power System Transient Stability Study
What is Power System Transient Stability Study?
Transient stability study is studies and analysis of the response of a system to
disturbances such as loss of generation, line-switching operations, faults, and sudden
load changes in the first few seconds after a disturbance. After the disturbance, the
synchronous machine frequency experiences a transient deviation from the
synchronous frequency. The purpose of the transient stability study is to determine
whether the machine will return to synchronous frequency after a disturbance –
Omazaki Engineering is a consultant serving the transient stability studies and analysis
stability analysis study consultant by sending an email to cs@omazaki.co.id or filling in
the form in contact. We conduct transient analysis study using ETAP software.
The ability of the power system to return to normal or stable conditions after a
disturbance is called stability. System disturbances can be of various types such as
sudden load changes, short-circuit between line and ground, line-to-channel
interference, third-channel interference, switching, etc.
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Power System Stability Classification
System stability mainly depends on synchronous machine behavior after a fault occurs.
The stability of the power system is mainly divided into two types depending on the
magnitude of the disturbance. The power system stability is classified as shown in the
figure below.
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of power systems. Contact Omazaki Engineering if you need a power system transient
Stability Steady-State
Ability to maintain synchronization between the engine in the system and the
external tie line after minor disturbances (load fluctuation, turbine regulator,
voltage regulator). The steady-state stability limit refers to the maximum power
Transient Stability
Ability to maintain synchronization between the engine in the system and the
external tie line after minor disturbances (load fluctuation, turbine regulator,
voltage regulator). The steady-state stability limit refers to the maximum power
that can be transferred through the system without losing stability.
Dynamic Stability
By using one of the many short circuit analysis software available, the system
data is input and the short circuit current at various points in the system is
calculated as output.
Transient Stability
Traditionally, transient stability is determined taking into account only the inherent
mechanical and electromagnetic characteristics of synchronous machines and the
impedance of the circuits connecting them. The response of the excitation or control
system to changes in generator speed or electrical output caused by system
disturbances is neglected. On the other hand, dynamic stability takes into account the
automatic voltage regulator and the response of the regulating system.
The traditional definition of transient stability is closely related to the ability of a system
to remain in sync for interference. Transient stability studies are usually carried out with
the assumption that the excitation time constants and the prime mover are longer
than the duration of the disturbance causing the instability.
System Fault That Can Cause System Instability
The most common disruptions that result in instability in industrial power systems are
(not necessarily in order of probability):
Short-circuit
Loss of a tie circuit to a public utility
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that can be transferred through the system without losing stability.
Loss of a tie circuit to a public utility
Loss of a portion of on-site generation
Starting a motor that is large relative to a system generating capacity
Switching operations
Impact loading on motors
The effect of each of these disturbances should be seen from the previous discussion of
the fundamentals of stability.
The Factors Can Affect Transient Stability
Generator WR2X rpm2 –– The greater this quantity the lower the acceleration
factor .
System Impedance — which must include the transient reactance of all
generating units. This affects phase angles and the flow of synchronizing power.
Duration of the fault — chosen as the criterion for stability. Duration will be
dependent upon the circuit-breaker speeds and the relay schemes used.
Generator loadings — prior to the fault which will determine the internal voltages
and the change in output.
System loading — which will determine the phase angles among the various
internal voltages of the generators.
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Importance of Transient Stability Analysis
The power system is designed to provide a continuous power supply that maintains
voltage stability. However, due to undesirable events, such as lightning, accidents or
other unforeseen events, a short circuit between the phase wires of the transmission
line or between the phase and ground wires that may occur is called a fault. Due to an
error, one or more generators may be severely disrupted causing an imbalance
between generation and demand. If the problem persists and is not resolved within the
predetermined time period, it can cause serious damage to the equipment which in
turn can lead to loss of power and blackout. Therefore, protective equipment is
installed to detect faults and clean / isolate the faulty part of the power system as
quickly as possible before the disturbance energy is distributed throughout the system.
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Abrupt decrease in electrical load on generators
Stability Problems In The Power System
Power system stability is a very important aspect to supply power continuously. It is
defined as a property of the power system that allows it to remain in a state of
state of equilibrium after a fault. Power system instability can occur in many different
situations depending on the system configuration and operating mode. One of the
stability problems is maintaining synchronous operation or synchronization, especially
power systems that rely on synchronous machines. This aspect is influenced by the
dynamics of the generator rotor angle and the power angle relationship. Another
instability problem you may encounter is the voltage collapse which is mostly related
to the load behavior and not the synchronous speed of the generator.
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Purpose and Objectives of Transient Stability Analysis
The power system operates closer and closer to its limits which makes instability
problems more likely. With this gift, it is very important to detect any disturbances that
can cause instability. Instability can occur during steady-state; However, this happens
more frequently after a short circuit which makes the time for cleaning up major
annoyances very short. That is, it is very important to determine whether the system
will be temporarily stable or will lose synchronization. Therefore, transient stability
analysis requires very fast computation and decision making.
Stability studies are helpful for determining the critical clean time of circuit breakers,
voltage levels, and system transfer capabilities.
The Transient Stability Study seeks to increase the reliability of the systems under study
by minimizing the damaging effects of transients that often occur in power systems
with the help of industry standard mitigation methods.
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Transient Stability Analysis Methods
Methods in transient stability analysis include swing equation, equal-area criterion,
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operating equilibrium under normal operating conditions and to regain an acceptable
y
y
g q
, q
,
numerical integration methods, and direct transient stability analysis methods.
Swing Equation
The swing equation describes the rotational dynamics of synchronous machines and is
relative positions of the rotor axis and the resultant axis are fixed. During a disturbance
in the engine, the rotor accelerates or decelerates in relation to the MMF of the
synchronous rotating air gap. The swing equation illustrates this relationship. The
power system swing equation is given as:
Equal-Area Criterion
Consider a single machine single-machine infinite bus (SMIB) in the Figure below. For
the system model considered in Figure below, it is not necessary to formally solve the
swing equation to determine whether the rotor angle is increasing indefinitely or
oscillating at an equilibrium position.
Numerical Integration Methods
The most commonly used method for solving swing equation 2.3 is numerical
integration. The initial condition for the differential equation to be solved is the swing
angle 0 (SEP) of Figure 2.8.
Direct Methods Transient Stability Analysis
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used in stability analysis to characterize those dynamics. During normal operation, the
Direct Methods Transient Stability Analysis
The method directly determines stability without explicitly solving the system’s
differential equations. This approach has received a lot of attention since Magnusson
and Aylett’s early work using the transient energy function for stability assessments.
Transient Stability Analysis Using Computer Software
Commonly Used Software
There are many software (software) available to conduct transient stability analysis
studies of electric power systems, including:
ETAP
SKM
EasyPower
DigSILENT
PSS®
Methodology
Data collection & verification
Site visit
System modeling
Model verification and validation
Simulation
Analysis
Reporting
Data Requirements
The data required to carry out a provisional power system transient stability study and
the recommended formats for organizing and presenting the information for the most
convenient use are discussed in detail in the application guide for specific stability
programs. The following is a summary of the generic class of data required. Note that
some of the more esoteric information is unimportant; eliminating them only limits the
accuracy of the results, especially at times greater than five times the duration of the
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studied interruption.
System data
Impedance (R + jX) of all critical transmission lines, cables, reactors and other
series components
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For All Significant Automatic Transformers and Transformers
kVA rating
Voltage ratio
Impedance
Voltage ratio
Winding connection
The tap is available and the tap is in use
For Load Tap Changing Regulators and Transformers
Load data: real and reactive electrical loads on all buses significant load on
system
Short circuit capacity (steady-state basis) of the utility supply, if any
kVAR from all significant capacitor banks
Description of normal and alternative switching settings
Rotating engine data
For Main Synchronous Machines
Mechanical and / or electric power rating (kVA, hp, kW, etc.)
Speed
The inertia constant H or inertia Wk2 of the rotating engine and the connected
load or prime mover
Speed torque curve or other load torque description, if motor
Real and reactive loading, if the generator is basic charged
Sub-transient, transient, and direct axis synchronous reactance
The quadrature axes of sub-transient, transient, and synchronous reactance
Sub-transient time constant and transient time on the direct and quadratic axes
Saturation information
Potier reactance
Data attenuation
Excitation system type time constant and limitation
Excitation system type, time constant, and limitation
Regulator and steam system or other types of prime mover, time constant and
limit
For Small Synchronous Machines
Speed
Direct axis synchronous reactance
For main induction machines or engine groups
Mechanical and/or electrical power rating
Positive-sequence equivalent sequence data (for example, R1, X1, XM)
Negative sequence equivalent data (e.g., R2, X2)
Load speed torque curve
Description of low voltage or other starting arrangement
For Small Induction Machines
Interference data
An overview of the disturbance to be studied, including (as applicable) the initial
transition status; error type, location, and duration; changing operations and
timing; manufacturer, type and arrangement of protective relays; and the
clearing times of the associated breakers
Study parameters
Study duration
Limits on acceptable voltage, current, or power swing
Integration interval
Output printing interval
Data output is required
Results (Deliverables) of the Transient Stability Study
Most stability programs provide the user with a large selection of outputs for printing.
This program can compute and print the following information as a function of time in
time domain analysis:
Voltage and voltage angles on all buses
The rotor angle, torque and engine speed are synchronous
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Inertia
The rotor angle, torque and engine speed are synchronous
Real, reactive power flows throughout the system
Bus frequency
Torque and slip of all induction machines
user selectable) during the study period.
The study value is strongly influenced by the selection of the appropriate printing
interval and the total duration of the simulation. Typically, a printing interval of 0.01 or
0.02 s is used; Longer intervals reduce solution time slightly, but increase the risk of
losing the rotor’s fast angular swing. The time it takes to get a solution is proportional
to the length or period studied, so this parameter must be strictly controlled for the
sake of the economy.
Avoiding long transient stability study periods is very
important especially if the systems and machines have
them roughly or incompletely represented as errors will
accumulate and render the results meaningless after
some point. A time limit of five times the duration of the
major disruption studied is generally long enough to
indicate whether the system is stable (in the sense of temporary stability) or not, while
keeping the solution time requirements to a reasonable level.
Frequency domain analysis will calculate the eigenvalues ​to determine the stability
characteristics of the system. For large utility systems, most programs can only provide
the dominant eigenvalues ​of the system. This information is sufficient for most stability
studies except for a multi-dominant eigenvalue situation.
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Contact Omazaki Engineering if you are looking for power system transient
stability study and analysis consultant to assist your new or existing project
in Indonesia and South East Asia.
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Related Articles:
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This user-selected result combination can be printed for each printing interval (also
Power System Study & Analysis
Load Flow Study & Analysis
Short-Circuit Study & Analysis
Protection Coordination Study
Motor Starting Study and Analysis
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Harmonic Study and Analysis
Arc Flash Study & Assessment
Power Quality Study & Assessment
Voltage Drop Study & Analysis
Voltage Imbalance (Unbalance) Study
References:
IEEE 1110-2019 – IEEE Guide for Synchronous Generator Modeling Practices and
Parameter Verification with Applications in Power System Stability Analyses
Hussain Hassan Al Marhoon, A Practical Method for Power Systems Transient
Stability and Security, Thesis Master of Science in Engineering Electrical of the
University of New Orleans.
Velimir Lackovic, Char. Eng., Power System Transient Stability Study
Fundamentals, Continuing Education and Development, Inc. 9 Greyridge Farm
Court, Stony Point, New York.
Factors affecting transient stability – Faults analysis, Electrical Engineering Portal
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