EE532 Power System Dynamics and Transients

1. EUMP Distance Education Services EE532 Power System Dynamics and Transients Satish J Ranade EE532 Lecture 1 (Ranade)

2. EE532 Power System Dynamics and Transients Objectives Understand basic aspects of power-system stability with focus on Electromechanical dynamics Transient and long term stability Voltage stability issues Obtain a feel for Stability analysis Interpretation of results EE532 Lecture 1 (Ranade)

3. EE532 Power System Dynamics and Transients Objectives Understand basics of electromagnetic transients with focus on Lightning Switching Calculation of response Over-voltages Obtain a feel for Insulation withstand concepts Standards Mitigation-Shielding, Line Design, Surge Arresters EE532 Lecture 1 (Ranade)

4. Time scale Phenomenon Result μS Lightning Overvoltage mS Switching Insulation Failure mS Abnormal Transient Fault .1 S Breaker Operations Instability 1 S Mechanical Dynamics Many Seconds Load Dynamics Collapse Power System Transients and Dynamics EE532 Lecture 1 (Ranade)

5. Power System Stability Definition (Ch.2) The ability of a power system to reach a new steady state or equilibrium after a disturbance. • Interconnected synchronous generators must settle to a common, constant speed • Voltages and power flow must settle to reasonable values ( otherwise relays will trip breakers) EE532 Lecture 1 (Ranade)

6. EE532 Lecture 1 (Ranade)

7. SPEED VOLT. STABLE UNSTABLE Power System Stability A disturbance, e.g., fault causes generator speeds, system voltages and power flow to change over time Stability  post-disturbance quantities become constant EE532 Lecture 1 (Ranade)

8. SPEED Line Real Power P Power System Stability Pm Pe Manifestations – Angle Stability Large System ‘Infinite Bus’ Voltage and frequency ~constant V Fault Occurs – Generator Terminal voltage V goes to zero Generator electrical real power output Pe goes to zero Turbine is still putting out mechanical power Pm Generator speeds up – builds up kinetic energy Fault is cleared Can generator get back to constant --synchronous speed? Time scale of 1-10 Seconds EE532 Lecture 1 (Ranade)

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10. Power System Stability P Manifestations – Angle Stability KE Builds up P Excess KE Needs to be removed Can generator get back to constant --synchronous speed? Only if it can get rid of excess KE Excess KE needs to go into the infinite bus through the line? Will it? What happens if it can’t? Stability means returning to synchronous speed In a multi-machine system it means settling at a common speed SPEED Line Real Power P EE532 Lecture 1 (Ranade)

11. Power System Stability P Manifestations – Angle Stability KE Builds up P Excess KE Needs to be removed The process of power transfer across the line to get rid of excess KE is inherently oscillatory The infinite bus is trying to “synchronize” the generator or “bring it back into step” Stability requires “synchronizing” torque In addition “damping torque “ to make oscillation decay – this comes from the machine as well as from control systems SPEED Line Real Power P EE532 Lecture 1 (Ranade)

12. Power System Stability Manifestations – Voltage Stability Line Opens Load Voltage Drops Many loads keep power constant --Current goes up Voltage drops further Reactive power loss goes up . Generator hits limit Generator voltage drops Voltage collapses Time scale of 1 seconds to minutes to hours EE532 Lecture 1 (Ranade)

13. Power System Stability First Swing (Transient Stability) Generator speeds swing around to common speed (Better definition later..)Little or no control action from exciters.. ~ 1 Second Transient Stability Multiple Swings 1-5 Sec; Field action most important Mid-Term Past 1 second control action is significant;Issue is oscillations and damping. This term is not used as much any more Long Term Past 1 second and including all control action Includes voltage stability effects This has become the standard study Terminology EE532 Lecture 1 (Ranade)

14. Power System Stability Rotor Angle Stability Refers to conditions in which generator dynamics is significant and voltages less important Steady state Stability Slow incremental changes that ultimately makes the system unstable ( associated with maximum power transfer) Small signal stability Response to small changes that can be analyzed using linear models. Terminology EE532 Lecture 1 (Ranade)

15. Power System Stability Voltage Stability Inability to maintain voltage because of reactive power deficit Voltage Collapse Voltage instability leading to low-voltage profile Terminology EE532 Lecture 1 (Ranade)

16. Power System Stability It’s all one big ball of wax! Distinctions are made for a number of reasons Ease of analysis or computation To emphasize/identify components and controls that have major impact A systems may be more prone to one type of stability than the other Modern long-term stability simulations capture most of the effects Comment on Terminology EE532 Lecture 1 (Ranade)

17. Power System Stability Purpose of Stability Study Planning Transmission Requirements Voltage Support ( VAR Supply) Design Controls– Excitation, Power system Stabilizers, FACTS devices Relay Settings Load Shedding Operations Operating Margins EE532 Lecture 1 (Ranade)

18. Fast transients • Lightning (uS) • Switching (mS) • Abnormal (mS – S) EE532 Lecture 1 (Ranade)

19. Fast transients • Lightning (uS) e Strokes to shield Induce voltage e Direct stroke to phase E ( back flashover) Strokes to ground Induce voltage Lightning strikes induces over voltages in a line by several mechanisms EE532 Lecture 1 (Ranade)

20. Fast transients Lightning Transmission Line Design issues Geometry to provide Adequate insulation Shield placement to eliminate Direct Stroke Surge arrester Grounding to minimize Induced voltage EE532 Lecture 1 (Ranade)

21. Fast transients Switching EE532 Lecture 1 (Ranade)

22. Fast transients Design issues ( Self Restoring Insulation) Probabilistic approach Stress Strength Probability of Failure EE532 Lecture 1 (Ranade)

23. Fast transients Design issues (Non Self Restoring Insulation) Insulation coordination kV Margin Equipment Withstand Prospective Surge (Limited by design, surge arresters,…) Time EE532 Lecture 1 (Ranade)

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25. Notes: Collaboration on Homework Assignments/Projects/Summaries is permitted. Do not provide or seek help from others on Tests. Violation of rule 4 will result in an automatic "F" grade and a recommendation for suspension. GRADING POLICY Homework Assigned each lecture, due following Monday 20% Tests 3 60% Projects 20% On Campus Students – Each unexcused absence will cost you 2% The grading scale is absolute 90 - 100 = A, 80 - 89 = B, 70 - 79 = C, 60 - 69 = D , < 60 = F ------------------------------------------------------------------------------------------------------------------ Late homework Policy: Unless prior arrangements are made, Late Homework Will Not Be Graded. However you will be given 50 % of the credit if you turn homework in prior to the next scheduled test. ------------------------------------------------------------------------------------------------------------------ EE532 Lecture 1 (Ranade)