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Transient Stability
1996-2010 Operation Technology, Inc. Workshop Notes: Transient Stability
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Topics
What is Transient Stability (TS)
What Causes System Unstable Effects When S stem Is Instable
Transient Stability Definition
ETAP TS Study Outputs
Power System TS Studies
Slide 21996-2010 Operation Technology, Inc. - Workshop Notes: Transient Stability
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What is Transient Stability
TS is also called Rotor Angle Stability
omet ng etween mec an ca system anelectrical system energy conversion
It is a Electromechanical Phenomenon
Time frame in milliseconds
All Synchronous Machines Must Remain inS nchronism with One Another
Synchronous generators and motors
Slide 31996-2010 Operation Technology, Inc. - Workshop Notes: Transient Stability
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What is Transient Stability
Torque Equation (generator case)
T = mechanical torque
=
air= air-gap flux
F = rotor field MMF
= rotor angle
Slide 41996-2010 Operation Technology, Inc. - Workshop Notes: Transient Stability
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What is Transient Stability
Swing Equation
=
D = damping constant
mech =Pelec = output electrical power
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What Causes System Unstable
From Torque Equation
pr me mover
Rotor MMF (field winding)
Air-Gap Flux (electrical system)
From Swin E uationPmech
Different time constants in mechanical and
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What Causes System Unstable
In real operation
ort-c rcu t
Loss of excitation
Prime mover failure
Loss of utility connectionsLoss of a portion of in-plant generation
Startin of a lar e motor
Switching operations
Slide 71996-2010 Operation Technology, Inc. - Workshop Notes: Transient Stability
Sudden large change in load and generation
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Effects When System Is Instable
Swing in Rotor Angle (as well as in V, I, P, Q
Case 1: Steady-state stableCase 2: Transient stableCase 3: Small-si nal unstable
Slide 81996-2010 Operation Technology, Inc. - Workshop Notes: Transient Stability
Case 4: First swing unstable
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Effects When System Is Instable
A 2-Machine
= - (Out-of-Step,
Slide 91996-2010 Operation Technology, Inc. - Workshop Notes: Transient Stability
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Effects When System Is Instable
Synchronous machine slip poles
Power swing
Misoperation of protective devices
Low-voltage conditions motor drop-offs
Damage to equipment Area wide blackout
Slide 101996-2010 Operation Technology, Inc. - Workshop Notes: Transient Stability
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Transient Stability Definition
Examine One Generator
Power Output Capability Curve
Slide 111996-2010 Operation Technology, Inc. - Workshop Notes: Transient Stability
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Transient Stability Definition
Transient and Dynamic Stability Limit
After a severe disturbance, the synchronousgenerator reaches a steady-state operatingcondition without a prolonged loss of
synchronism Limit: < 180 during swing
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Modeling and Data Preparation
Synchronous Machine
Machine
Exciter and AVR
Prime Mover and Governor / Load Torque
Slide 131996-2010 Operation Technology, Inc. - Workshop Notes: Transient Stability
Power System Stabilizer (PSS) (Generator)
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Modeling and Data Preparation
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Modeling and Data Preparation
Typical synchronous machine data
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Modeling and Data Preparation
Induction Machine
Machine Load Tor ue
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Modeling and Data Preparation
Power Grid
Short-Circuit Capability Fixed internal volta e and infinite inertia
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Modeling and Data Preparation
Load
Voltage dependency Fre uenc de endenc
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Modeling and Data Preparation
Load
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Modeling and Data Preparation
Events and Actions
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Modeling and Data Preparation
Device Type Action
Bus 3-P Fault L-G Fault Clear Fault
Branch Fraction
Fault
Clear
Fault
PD Trip Close
Generator Droop /Isoch
Start Loss Exc. P Change V Change Delete
Grid P Change V Change Deleteotor cce erate oa
Changee ete
Lumped Load LoadChan e
Delete
MOV Start
Wind Turbine Disturbance Gust Ramp
Slide 211996-2010 Operation Technology, Inc. - Workshop Notes: Transient Stability
MG Set Emergency Main
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Power System TS Studies
Fault3-phase and single phase fault
Clear fault
Critical Fault Clearing Time (CFCT)
Bus Transfer
Fast load transferrin Load SheddingUnder-frequency
n er-vo age Motor Dynamic Acceleration
Slide 221996-2010 Operation Technology, Inc. - Workshop Notes: Transient Stability
Synchronous motor
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Power System TS Studies
Critical Fault Clearing Time (CFCT)
Clear faultClear fault
1 cycle1 cycle
Clear faultClear faultFault
unstable
unstable
Cycle
unstable
stableCFCT
Critical Separation Time (CSST)SeparationSeparationSeparationSeparationFault
un
un
1 cycle
un
st
1 cycle
Slide 231996-2010 Operation Technology, Inc. - Workshop Notes: Transient Stability
stable
stable
stable
bleCSST
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Power System TS Studies
Fast Bus Transfer
1
Motor residual voltage
0
0.2
0.4
0.6
0.8
Vmotor
-0.8
-0.6
-0.4
-0.2
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1s
-1
Slide 241996-2010 Operation Technology, Inc. - Workshop Notes: Transient Stability
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Power System TS Studies
Fast Bus Transfer
ES = System equivalent per unitvolts per hertz
M =hertz
ER = Resultant vectorial voltage
rans er
90 degrees
Slide 251996-2010 Operation Technology, Inc. - Workshop Notes: Transient Stability
R .
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Power System TS Studies
Load Shedding
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Power System TS Studies
Motor Dynamic Acceleration
mpor an or s an e sys em opera on
Motor starting impact
Generator AVR action
Reacceleration
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Solution to Stability Problems
Improve System Design
ncrease sync ron z ng power
Design and Selection of Rotating Equipment
Use of induction machines
Increase moment of inertia Reduce transient reactance
characteristics
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Solution to Stability Problems
Application of Power System Stabilizer
Add System Protections
Fast fault clearance
Load shedding System separation
- f- r l
Slide 291996-2010 Operation Technology, Inc. - Workshop Notes: Transient Stability
