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Premium member Presentation Transcript Slide 1: UNDERVOLTAGE LOAD SHEDDING CHUCK MOZINA CONSULTANT BECKWITH ELECTRIC Slide 2: BLACKOUTS HOW AND WHY THEY OCCUR WHY VOLTAGE RATHER THAN FREQUENCY IS THE LEADING EDGE INDICATOR OF COLLAPSE RECENT BLACKOUTS : RECENT BLACKOUTS 2003 - East Coast Blackout 2003 - Italian Blackout 2002 - Swedish Blackout 1997 - PJM Disturbance 1996 - West Coast Blackout 1995 - PECO Disturbance 1987 - City of Memphis ROOT CAUSE OF RECENT BLACKOUTS : ROOT CAUSE OF RECENT BLACKOUTS VOLTAGE COLLAPSE -- WHY Today Major Generation Sources are Remote From Load Centers.This Was Not the Case 35 Years Ago. This Makes the Power System is Very Reliant on Transmission System to Transport Power to Load Centers ROOT CAUSE OF RECENT BLACKOUTS VOLTAGE COLLAPSE -- WHY : ROOT CAUSE OF RECENT BLACKOUTS VOLTAGE COLLAPSE -- WHY Purchase Power from Remote Sources to Save $$$. New Generation Built Remote from Load Centers Utility Load are Increasing made up of Air Conditioning Motors Susceptible to Stall Conditions due to Transmission System Faults Real Power (MW) Flow : Real Power (MW) Flow Real Power (MW) Flow Example : Real Power (MW) Flow Example Real Power (MW) Flow Example : Real Power (MW) Flow Example Reactive Power (Mvars) Flow : Reactive Power (Mvars) Flow Sources of Reactive (Var) Support : Sources of Reactive (Var) Support Var Support Must be Provided at the Load Center. Two Major Sources of Var Support Capacitor Banks – Double Edge Sword. Vars go Down with the Square of Voltage. Generators/ Synch. Condensers – A Dynamic Source of Vars. Can Adjust Var Output During Contingencies RECENT BLACKOUTSREVISITED : RECENT BLACKOUTSREVISITED 2003 - East Coast Blackout 2003 - Italian Blackout 2002 - Swedish Blackout 1997 - PJM Disturbance* 1996 - West Coast Blackout 1995 - PECO Disturbance* 1987 - City of Memphis* * Rapid Voltage Collapse How Load Responds to Low VoltageBasic Power System : How Load Responds to Low VoltageBasic Power System How Load Responds to Low Voltage : How Load Responds to Low Voltage Resistive Load Current Decreases as Voltage Goes Down Helping the System. Motor Loads are Constant KVA Devices and Increase Their Load Current as Voltage Decreases Hurting the System. During “Heat Storm” Conditions Most Load is Motor Load Making Blackout More Likely. Example of Voltage Recovery From a Transmission Fault- Rapid Voltage Collapse : Example of Voltage Recovery From a Transmission Fault- Rapid Voltage Collapse POWER SYSTEM INSTABILITIES : POWER SYSTEM INSTABILITIES Four Types of Instability: Voltage* Steady State * Transient Dynamic *Involved in Recent Blackouts VOLTAGE COLLASPE SCENERIO : VOLTAGE COLLASPE SCENERIO VOLTAGE COLLASPE SCENERIO : VOLTAGE COLLASPE SCENERIO VOLTAGE COLLASPE SCENERIO : VOLTAGE COLLASPE SCENERIO Steady State Instability : Steady State Instability Steady State Instability : Steady State Instability Steady State Instability : Steady State Instability UNDERVOLTAGE LOAD SHEDDING (UVLS) : UNDERVOLTAGE LOAD SHEDDING (UVLS) UNDERVOLTAGE LOAD SHEDDING (UVLS) : UNDERVOLTAGE LOAD SHEDDING (UVLS) ATTEMPT TO BALANCE MVAR LOAD WITH MVAR SOURCES BY SHEDDING LOAD. TWO TYPES OF UVLS SCHEMES: Decentralized - Relays Measure Voltage at load to be shed. Centralized – Relays Measure Voltage at Key Locations. Voltage transmitted to Central Location and combined with other System Information. Schemes Called SPS or Wide Area Protection. STATUS OF UNDERVOLTAGE LOAD SHEDDING (UVLS) : STATUS OF UNDERVOLTAGE LOAD SHEDDING (UVLS) NERC - UVLS Not Mandatory - Recognized as a Cost-effective Method to Address Voltage Collapse. - Allowed Region to Establish Policy WECC - Most Aggressive in UVLS - Established UVLS Guidelines UVLS AT UTITITIES : UVLS AT UTITITIES Centralized Decentralized - BC Hydro - Puget Sound - Hydro Quebec - First Energy - Entergy - Public Service of New Mexico - PG&E DESIGNING A SECURE UVLS SCHEME : DESIGNING A SECURE UVLS SCHEME Selection of Voltage Relays forUVLS : Selection of Voltage Relays forUVLS Measure all Three Voltage or Positive Sequence Voltage. Use Low Voltage Cutoff. Consider Negative Sequence Blocking. Start Timer only if Voltage is Within Window. Use Relay with High Reset Ratio. Digital Voltage Relay are ideal for This Application. Three-Phase UVLS Logic : Three-Phase UVLS Logic Positive Sequence UVLS Logic : Positive Sequence UVLS Logic V1 = 1/3 ( Va + aVb +a2Vc ) Where: Va,Vb,Vc are line-to-neutral voltages a = 1l120o a2 = 1l240o Balanced Conditions: V1=Va=Vb=Vc. Point of Voltage Measurement : Point of Voltage Measurement UVLS SETTING CONSIDERATIONS : UVLS SETTING CONSIDERATIONS UVLS Setting Considerations : UVLS Setting Considerations Relay Engineers Must Work Closely With System Planning Engineers to Design UVLS. Planning Engineers Have the Load Flow Data Required to Determine the Voltage Measurement Locations and Amount of Load to Shed. They also develope the P-V (Nose Curve) that will determine the Voltage Relay Pickup Setting. Time Delay for UVLS are Typically in the 2-10 Sec. Range – not in Cycles Range for UFLS. Undervoltage Relay Pickup : Undervoltage Relay Pickup Coordinating UVLS Relay Pickup : Coordinating UVLS Relay Pickup CONCLUSIONS : CONCLUSIONS Voltage Collapse is the Major Cause of Blackouts in US Power Systems. UVLS is a Viable Method of Providing Protection to Avoid Slow Voltage Collapse Situations. UVLS Maybe too Slow to respond to Rapid Fault Induced Voltage Collapses. UVLS Requires close Cooperation Between Planners and Relay Engs. UVLS Schemes are More Difficult to Design and Set than UFLS. UNDERVOTAGELOAD SHEDDING : UNDERVOTAGELOAD SHEDDING THE END??? Questions ??? You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.