classification of power system stability and synchronies machine modeling

1. Power System Dynamics and Transients
Term Paper Presentation
On
‘ Classification of power system stability and synchronous machine modeling’
By Nebiyu Y.
5/31/2021
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2. Introduction
 Power system stability is ability of power system to maintain synchronous operation following a severe disturbance.
 Synchronous machines may be modeled for the study of stability analysis :
 Availability of the dynamics of the field circuit
 Rotor damper circuits
 Excitation system
 Considerations for Classifying power system stability
 The physical nature of the resulting instability
 The size of disturbance considered
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3.  Based on nature of resulting instability
 Rotoranglestability
 Smalldisturbance anglestability
 Transientstability
 Voltagestability
 Smalldisturbance voltagestability
 Largedisturbance voltagestability
 Frequencystability
 Shortterm frequencystability
 Longterm frequencystability 5/31/2021
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4. Rotor Angle stability
 It is an ability to remain in synchronism after being subjected to sudden or large changes in rotor
angle.
 Synchronous machines maintain synchronism by developing restoring torques
 Lack of sufficient synchronizing torque results in aperiodic instability
 Lack of damping torque results in oscillatory instability
 At equilibrium, Input Tm equalsoutput EMT of each generator.
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5. Large-disturbance angle stability
 To maintain synchronism during transient fault on
 Transmission circuit
 Loss of a large generator
 System response involves large excursions of generator rotor angles.
 Limited to about 3 to 5 seconds following the disturbance.
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6. Small-disturbance angle stability
 To maintain Synchronism under small disturbances
 Causes of small disturbance angle stability
 lack of sufficient synchronizing torque
 lack of sufficient damping torque
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7. Voltage stability
 ability of a power system to maintain steady acceptable voltages at all buses.
 Causes of voltage instability
 Improper balance of reactive power throughout the system.
 Characteristics of system loads
 Voltage control devices
 Generators excitation system.
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8. Large-disturbance voltage stability
 Maintain steady voltages following severe disturbances.
 systemfaults, lossof generation, or circuitcontingencies.
 Involve Slower acting equipment .
 The study period may extend from a few seconds to several minutes.
Small-disturbance voltage stability
 A system’s ability to maintain steady voltages following small disturbances.
 Incremental changes in load. 5/31/2021
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9. Frequency stability
 Maintain the frequency within a nominal range following a severe system.
 Restore balance between system generation and load with minimum loss of load .
 Frequency stability problem are associated with
 Equipment responses
 Poor coordination of control and protection systems.
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10. Modeling requirements for synchronous machines
 For small-disturbance rotor-angle stability analysis, accurate representation of the field circuit as well
as the rotor damper circuits is important
 For voltage stability studies, the voltage control and reactive power supply capabilities of generators
are of prime importance.
 Frequency stability problems are generally associated with inadequacies in equipment response and
poor coordination of control and protection equipment
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11. Conclusion
 Stability of an interconnected system is determined by
 Overall response of the system as evidenced by its mean frequency.
 The generator models used should be capable of accurately representing
 Under conditions of large variations in voltage and frequency
 Responses of control and protective devices
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