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EE 3043 Power Systems III

Power System Stability Introduction

by

Dr. Lidula N. Widangama Arachchige Department of Electrical Engineering

University of Moratuwa, Sri Lanka

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Power Systems III - Course Outline

Module Objectives To evaluate and predict the stability of a power system

To recognize the requirement of protection of power systems and to determine the protective relaying equipment/methods require at different levels of the power system.

To design a protective relay scheme for a simple power system and validate its accuracy through a simulation study, which need be modeled using commercial power systems software.

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Power Systems III - Course Outline

Learning Outcomes After completing this module the student should be able to

demonstrate knowledge of power system stability, factors that influence system stability and methods to improve and maintain stability

evaluate and predict the stability of a power system

demonstrate knowledge of the general requirements of protective relaying

select suitable instrument transformers for metering and protection, optimization of their protection functions

demonstrate knowledge of relaying principles of electro-mechanical, static and numeric relays

to calculate the relay settings and design protection schemes using over current relays

Identify earth fault and directional relay requirements

identify appropriate protection schemes for generators and transformers

apply different relay techniques for protection from distance faults

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Power Systems III - Course Outline

Method of Assessment

Continuous assessment (30%) ~5 Assignments

Includes in-class tests

Includes 1 PSCAD/EMTDC simulation assignment

Final written exam (70%)

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Power Systems III - Course Outline

References

Prabha Kundur, Power System Stability and Control, Tata McGraw Hill Education Private Limited, New Delhi, India, 2010, ISBN 0 07 063515 3. (for Stability)

Juan M. Gers and Edward J Holms, Protection of Electricity Distribution Networks, 2nd Edition, IET Power and Energy Series 47, IEEE, London, UK, 2011, ISBN 0 86341 537 7. (for Protection)

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Power System

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Single-line diagram of a Power System

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Power Quality and Reliability

A properly designed and operated power system should maintain the quality of power supplied, withholding to

constant voltage

constant frequency

level of reliability

specified in the standards

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Power System Controls

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Power Systems Stability

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Power System Stability

The stability of an interconnected power system is its ability to maintain acceptable operating conditions under normal operation and after being subjected to a disturbance

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Classification of Power System Stability

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Rotor Angle Stability

Ability of the interconnected synchronous machines in a power system to remain in synchronism

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Schematic Diagram Of a 3 Synchronous Machine

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Definition of the Rotor Angle

Fr Field mmf

Fs Armature mmf

Fsr Resultant airgap mmf

E Excitation Voltage

Ear = jXarIa Armature Reaction Voltage

Esr On-load emf

V Terminal Voltage

RaIa Resistive Voltage Drop

XlIa Leakage Reactance Voltage Drop

Cos = Power Factor at the Generator Terminal

E = V + RaIa + j(Xl + Xar) Ia

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Fr

E

Fs

Fsr

Esr Ear = XarIa

XlIa RaIa

V

Ia

r

r

Synchronous Reactance, Xs

Rotor Angle = r

Rotor Angle, r

The angle between E and Esr is equal to the angle between Fr and Fsr which is known as the Rotor Angle If Fr leads Fsr by an angle r machine operates as a generator

If Fr lags Fsr by an angle r machine operates as a motor

Power developed by the machine = P P

therfore, is also known as the Power Angle

Usually, P is considered

because leakage impedance is very small compared to magnetization reactance

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