Fundamentals of Transmission Operations System Stability PJM State & Member Training Dept. PJM©2013 5/2/2014 Objectives Following this presentation, the student will be able to: • Define stable operation • Define the following stability modes: Steady state, Transient, Dynamic • Discuss the actions that may be taken by the System Operator that will impact the stability of the system • Discuss how instability threatens the system PJM©2013 5/2/2014 Stable Operation • Definition • Generic • Stability is the condition of equilibrium between opposing forces • In power system, Mechanical power provided to turbine = electrical power drawn by the system • Typical Threats to Stability • • • • PJM©2013 Loss of one or more generators Loss of one or more major pieces of equipment System faults Low voltage operation 5/2/2014 Steady State Stability • Definition of Steady State • • • • PJM©2013 Steady loads Steady generation balanced with load No disturbances Small, slow changes are part of steady state 5/2/2014 Steady State Stability • Relationship of Phase Angle to Steady State Stability • Review of power flow equation Generator Bus PJM©2013 Equivalent System 5/2/2014 Steady State Stability • Relationship of Phase Angle to Steady State Stability • Magnitude of power flow as a function of angle Unstable Area PJM©2013 5/2/2014 Steady State Stability • Relationship of Phase Angle to Steady State Stability • Stability Margin Difference between operating point and 90 degrees PJM©2013 5/2/2014 Steady State Stability • Relationship of Phase Angle to Steady State Stability • Effect of varying MW output PJM©2013 5/2/2014 Steady State Stability • Relationship of Phase Angle to Steady State Stability • Effect of removing one line from service PJM©2013 5/2/2014 Steady State Stability • Relationship of Voltage to Steady State Stability • Effect of changing machine excitation PJM©2013 5/2/2014 Steady State Stability PJM©2013 5/2/2014 Transient Stability • Definition • The ability of a generator or group of generators to remain in synchronism immediately following a system disturbance (initial swing) • Transient stability is typically viewed as first swing stability • The first swing for a generator takes less than a second PJM©2013 5/2/2014 Transient Stability • Equal Area Criterion (Area ABC=CDE) PJM©2013 5/2/2014 Transient Stability PJM©2013 5/2/2014 Dynamic Stability • Definition • Ability of generators to damp oscillations caused by relatively minor disturbances through the action of properly tuned control systems • Mechanisms • Excitation control • Governors • Protective relaying PJM©2013 5/2/2014 Dynamic Stability PJM©2013 5/2/2014 135 130 125 120 115 110 105 100 95 90 85 80 75 PJM©2013 10:20:00 UNIT7 10:19:00 10:18:00 10:17:00 UNIT6 10:16:00 10:15:00 10:14:00 UNIT5 10:13:00 10:12:00 UNIT4 10:11:00 10:10:00 10:09:00 UNIT3 10:08:00 10:07:00 10:06:00 UNIT2 10:05:00 10:04:00 10:03:00 UNIT1 10:02:00 10:01:00 10:00:00 Gen. Dynamic Stability Muddy Run - 12/28/99 UNIT8 Time 5/2/2014 Dynamic Stability Peach Bottom Units - 12/28/99 Peach Bot #3 Muddy Run Tot Gen. 700 600 500 400 Gen. Peach Bot #2 1150 1140 1130 1120 1110 1100 1090 1080 1070 1060 1050 1040 300 200 Time PJM©2013 10:11:00 10:12:00 10:13:00 10:14:00 10:15:00 10:16:00 10:17:00 10:18:00 10:19:00 10:20:00 10:00:00 10:01:00 10:02:00 10:03:00 10:04:00 10:05:00 10:06:00 10:07:00 10:08:00 10:09:00 10:10:00 100 0 5/2/2014 Dynamic Stability Peach Bottom xfmr Switching - 3/23/01 1200 1100 1000 900 800 PB 02 MW PB 02 MV MW/MVAR 700 PB 03 MW PB 03 MV 600 Slm 1 MW Slm 1 MV 500 Slm 2 MW Slm 2 MV 400 MR Gen Cono Gen 300 200 100 9:00 8:56 8:52 8:48 8:44 8:40 8:36 8:32 8:28 8:24 8:20 8:16 8:12 8:08 8:04 8:00 7:56 7:52 7:48 7:44 7:40 7:36 7:32 7:28 7:24 7:20 7:16 7:12 7:08 7:04 7:00 0 Time PJM©2013 5/2/2014 Consequences of Instability • Loss of synchronization • Steady state • phase angle exceeds 90 degrees • Transient • excessive rotor angle swings • units tripped following disturbance • Dynamic • continued oscillations over long periods of time • may damage units before they are tripped PJM©2013 5/2/2014 Consequences of Instability • Operator Actions Affecting Stability • Awareness • Generator MW output • Decrease MW output to increase stability • Generator MVAR output • Increase MVAR output to increase stability • Lines in service - system strength • Put more lines in service to increase stability • Special Relay schemes PJM©2013 5/2/2014 Stability Guides • Transmission Operations Manual – Section 5 • • • • • • • • • PJM©2013 Calvert Cliffs Voltage Limitations Indian River #4 “Trip a Unit” Special Protection Scheme Conemaugh Unit Stability Conemaugh #2 Unit Stability Trip Scheme - Conemaugh-Juniata 500 kV Outage PL Northern Generation Stability PSE&G Artificial Island Stability Rockport Operating Guide Quad Cities Stability Operations Many others….. 5/2/2014 Stability and the PJM Generator Interconnection Process • What do these guidelines contain? • Unit restrictions for each outage that affects stability • Tripping schemes • Generator MW output restrictions • Generator MVAR output restrictions PJM©2013 5/2/2014 Stability and the PJM Generator Interconnection Process • How are these guides developed? • Guidelines are based on detailed stability studies that consider severe fault conditions (N-1) that occur under each significant outage condition (N-2) in the area of concern • Guidelines are developed under very conservative assumptions of generation dispatch and load level PJM©2013 5/2/2014 Stability and the PJM Generator Interconnection Process • When are these guides updated and developed? • Guides will be updated every time a new generator locates in vicinity of problem • Anytime an area becomes concentrated with a large amount of generation relative to the transmission outlet capability of the area, a detailed stability study will be performed to see if an operating guide is needed PJM©2013 5/2/2014 Stability and the PJM Generator Interconnection Process • Why are these guides so important? • Guides usually involve several large generators that can easily be damaged when they are operated out-of-step with the rest of the system • A generator that is operated out-of-step will frequently cause transmission lines to trip before the generator itself trips off-line • When several large generators are operated out-of-step, cascading outages and widespread load shedding can result due to the fluctuations in power flows, voltage and frequency PJM©2013 5/2/2014 Stability and the PJM Generator Interconnection Process • Conclusion: • Stability has not yet become the most significant system limitation • Operators need to be aware of the importance of why stability operating guides are developed and why they will be updated much more frequently than in the past PJM©2013 5/2/2014 The ability of a generator to dampen out oscillations caused by minor disturbances is called: 1. 2. 3. 4. Steady State Stability Transient Stability Dynamic Stability Generator Stability 0 of 80 25% 25% 25% 25% Steady State Stab... Transient Stability Dynamic Stability Generator Stability The ability of a generator to remain in synchronism immediately following a system disturbance is: 1. 2. 3. 4. Steady State Stability Transient Stability Dynamic Stability Generator Stability 0 of 80 25% 25% 25% 25% Steady State Stab... Transient Stability Dynamic Stability Generator Stability Questions? PJM©2013 5/2/2014 Disclaimer: PJM has made all efforts possible to accurately document all information in this presentation. The information seen here does not supersede the PJM Operating Agreement or the PJM Tariff both of which can be found by accessing: http://www.pjm.com/documents/agreements/pjmagreements.aspx For additional detailed information on any of the topics discussed, please refer to the appropriate PJM manual which can be found by accessing: http://www.pjm.com/documents/manuals.aspx PJM©2013 5/2/2014