11 - transient stability

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ETAP 5.0Transient Stability

Copyright 2003 Operation Technology, Inc.

Time Frame of Power System Dynamic Phenomena

Copyright 2003 Operation Technology, Inc. Workshop Notes: Transient Stability

Slide 2

Introduction TS is also called Rotor Stability, Dynamic Stability Electromechanical Phenomenon All synchronous machines must remain in synchronism with one another TS is no longer only the utilitys concern Co-generation plants face TS problems

Copyright 2003 Operation Technology, Inc. Workshop Notes: Transient Stability

Slide 3

Analogy

Which vehicles will pushed hardest? How much energy gained by each vehicle? Which direction will they move? Height of the hill must they climb to go over?Slide 4

Copyright 2003 Operation Technology, Inc. Workshop Notes: Transient Stability

Introduction (contd) System protection requires consideration of:Critical Fault Clearing Time (CFCT) Critical Separation Time (CST) Fast load transferring Load Shedding

Copyright 2003 Operation Technology, Inc. Workshop Notes: Transient Stability

Slide 5

Causes of Instability Short-circuits Loss of utility connections Loss of a portion of in-plant generation Starting of a large motor Switching operations (lines or capacitors) Impact loading on motors Sudden large change in load and generation

Copyright 2003 Operation Technology, Inc. Workshop Notes: Transient Stability

Slide 6

Consequences of Instability Synchronous machine slip poles generator tripping Power swing Misoperation of protective devices Interruption of critical loads Low-voltage conditions motor drop-offs Damage to equipment Area wide blackout Copyright 2003 Operation Technology, Inc. Workshop Notes: Transient Stability Slide 7

Synchronous Machines Torque Equation (generator case)

T = mechanical torque P = number of poles

air = air-gap fluxFr = rotor field MMF

= rotor angle

Copyright 2003 Operation Technology, Inc. Workshop Notes: Transient Stability

Slide 8

Swing Equation

Copyright 2003 Operation Technology, Inc. Workshop Notes: Transient Stability

Slide 9

Synchronous Machines (contd) Swing Equation

M D Pmech Pelec

= inertia constant = damping constant = input mechanical power = output electrical powerSlide 10

Copyright 2003 Operation Technology, Inc. Workshop Notes: Transient Stability

Rotor Angle Responses

Case 1: Steady-state stable Case 2: Transient stable Case 3: Small-signal unstable Case 4: First swing unstableSlide 11

Copyright 2003 Operation Technology, Inc. Workshop Notes: Transient Stability

Power and Rotor Angle (Classical 2-Machine Example)

Copyright 2003 Operation Technology, Inc. Workshop Notes: Transient Stability

Slide 12

Power and Rotor Angle (contd)

Copyright 2003 Operation Technology, Inc. Workshop Notes: Transient Stability

Slide 13

Power and Rotor Angle (Parallel Lines)

Copyright 2003 Operation Technology, Inc. Workshop Notes: Transient Stability

Slide 14

Both Lines In Service

Copyright 2003 Operation Technology, Inc. Workshop Notes: Transient Stability

Slide 15

One Line Out of Service

Copyright 2003 Operation Technology, Inc. Workshop Notes: Transient Stability

Slide 16

Equal Area Criterion

Copyright 2003 Operation Technology, Inc. Workshop Notes: Transient Stability

Slide 17

Equal Area Criterion

Copyright 2003 Operation Technology, Inc. Workshop Notes: Transient Stability

Slide 18

Equal Area - Stable

Copyright 2003 Operation Technology, Inc. Workshop Notes: Transient Stability

Slide 19

Equal Area Unstable

Copyright 2003 Operation Technology, Inc. Workshop Notes: Transient Stability

Slide 20

Equal Area - Unstable

Copyright 2003 Operation Technology, Inc. Workshop Notes: Transient Stability

Slide 21

Power System Stability Limit Steady-State Stability LimitAfter small disturbance, the synchronous generator reaches a steady state operating condition identical or close to the predisturbance Limit: < 90

Copyright 2003 Operation Technology, Inc. Workshop Notes: Transient Stability

Slide 22

Power System Stability Limit (cond) Transient and Dynamic Stability LimitAfter a severe disturbance, the synchronous generator reaches a steady-state operating condition without a prolonged loss of synchronism Limit: < 180 during swing

Copyright 2003 Operation Technology, Inc. Workshop Notes: Transient Stability

Slide 23

Generator Modeling

MachineEquivalent Model / Transient Model / Subtransient Model

Exciter and Automatic Voltage Regulator (AVR) Prime Mover and Speed Governor Power System Stabilizer (PSS)Copyright 2003 Operation Technology, Inc. Workshop Notes: Transient Stability Slide 24

Generator Modeling (cond) Typical synchronous machine data

Copyright 2003 Operation Technology, Inc. Workshop Notes: Transient Stability

Slide 25

Factors Influencing TS Post-Disturbance Reactance seen from generator.Reactance Pmax

Duration of the fault clearing time.Fault time Rotor Acceleration Kinetic Energy Dissipation Time during deceleration

Generator Inertia.Inertia Rate of change of Angle Kinetic Energy Generator Internal Voltage Internal Voltage Pmax

Copyright 2003 Operation Technology, Inc. Workshop Notes: Transient Stability

Slide 26

Factors Influencing TS Generator Loading Prior To DisturbanceLoading Closer to Pmax. Unstable during acceleration

Generator Internal ReactanceReactance Peak Power Initial Rotor Angle Dissipation Time during deceleration

Generator Output During FaultFunction of Fault Location and Type of Fault

Copyright 2003 Operation Technology, Inc. Workshop Notes: Transient Stability

Slide 27

Solution to Stability Problems Improve system designIncrease synchronizing power

Design and selection of rotating equipmentUse of induction machines Increase moment of inertia Reduce transient reactance Improve voltage regulator and exciter characteristics

Copyright 2003 Operation Technology, Inc. Workshop Notes: Transient Stability

Slide 28

Solution to Stability Problems Reduction of Transmission System Reactance High Speed Fault Clearing Dynamic Braking Regulate Shunt Compensation Steam Turbine Fast Valving Generator Tripping Adjustable Speed Synchronous MachinesCopyright 2003 Operation Technology, Inc. Workshop Notes: Transient Stability Slide 29

Solution to Stability Problems HVDC Link Control Current Injection from VSI devices Application of Power System Stabilizer (PSS) Add system protectionsFast fault clearance Load Shedding System separationCopyright 2003 Operation Technology, Inc. Workshop Notes: Transient Stability Slide 30

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