Volt VAR Control & Optimization. Bob Uluski Quanta Technology Quanta Technology LLC

Transcription

1 Volt VAR Control & Optimization Bob Uluski Quanta Technology

2 What is Volt VAR control? Volt VAR control (VVC) is a fundamental operating requirement of all electric distribution systems The prime purpose of VVC is to maintain acceptable voltage at all points along the distribution feeder under all loading conditions LTC Primary Feeder SUBSTATION First Customer Distribution Transformer Secondary Service Drop Wires Last Customer Voltage volts Primary volts distribution First Customer transformer Last Customer 114 ANSI C84.1 Lower Limit (114 volts) Distance 1 volt secondary 1 volt service drop

3 What is Volt VAR control? Without VVC: Voltage might be okay during average load Transformer Tap Position i 126V 120V 114V S E F F C D S L C

4 What is Volt VAR control? Without VVC: voltage might droop below the minimum acceptable level for some customers during heavy load periods Transformer Tap Position i 126V 120V 114V Low Voltage S E F F C D S L C

5 What is Volt VAR control? Without VVC: Transformer Tap Position Could raise the manual tap setting on the substation transformer to correct thepeakloadproblem problem 126V 120V 114V S E F F C D S L C

6 What is Volt VAR control? Without VVC: But when feeder loading in light, high voltage could be a problem at the substation end of the feeder Transformer Tap Position High Voltage 126V 120V 114V S E F F C D S L C

7 Without VVC: What is Volt VAR control? But when feeder loading in light, high voltage could be a problem at the substation end of the feeder N VVAR C S Transformer Tap Position 126V 120V 114V S E F F C D S L C

8 VVC = Voltage Regulation + Reactive Power Compensation Use voltage regulators (Vregs) or transformers with load tap changers (LTCs) that automatically raise or lower the voltage in response to changes in load Use capacitor banks to supply some of the reactive power that would otherwise be drawn from the supply substations S D S E F

9 VVC in Today s Operating Environment (and Tomorrow s Operating Environment Too!) Maintaining the status quo no longer acceptable Utilities are seeking to do more with VVC than just keeping voltage within the allowable limits System optimization i is an important tpart of the normal operating strategy under smart grid As penetration of intermittentrenewable renewable generating resources grows in future, high speed dynamic volt VAR control will play a significant role in maintaining power quality and voltage stability onthe distribution feeders

10 Volt VAR Control in a Smart Grid World Expanded objectives for Volt VAR control include Basic requirement maintain acceptable voltage Support major Smart Grid objectives: Accomplish energy conservation Improve efficiency (reduce technical ll losses) Promote a self healing grid (VVC plays a role in maintaining voltage after self healing has occurred) Enable widespread deployment of Distributed ted generation, Renewables, Energy storage, and other distributed energy resources

11 Requirements for the Ideal Volt VAR System Maintain Acceptable Voltage Profile at all points along the distribution feeder under all loading conditions Maintain Acceptable Power Factor under all loading conditions Provide Self Monitoring alert dispatcher when a volt VAR device fil fails Allow Operator Override during system emergencies Work correctly followingfeeder Reconfiguration Accommodate Distributed Energy Resources Provide Optimal Coordinated Control of all Volt VAR devices Allow Selectable Operating Objectives as different needs arise

12 Approaches to Volt VAR Control Traditional Approach DLA Master Station Switched Capacitor Bank Distribution Power Flow SCADA Volt VAR Integrated Volt VAR IVVC Application Substation Transformer With Load Tap Changer Distribution SCADA Substation RTU Line Regulator Substation Capacitor Bank

13 Traditional Volt VAR Control Current/Voltage Sensor Distribution Primary Line Capacitor Bank Current/Voltage Sensor Voltage Regulator "Local" Current/ Voltage Measurements Standalone Controller On/Off Control Command Signal "Local" Current/ Voltage Measurements Standalone Controller On/Off Control Command Signal Volt VAR flows managed by individual, independent, standalone volt VAR regulating devices: Substation transformer load tap changers (LTCs) Line voltage regulators Fixed and switched capacitor banks

14 Limitations of Traditional Approach Power factor correction/loss reduction Many traditional cap bank controllers have voltage control (switch on when voltage is low) Reactive power controllers available, but expensive (need to add CT) Good at maintaining acceptable voltage Good at PF correction during peak load seasons may not come on at all during off peak seasons Result is that PF is usually great (near unity) during peak load periods and low during off peak seasons (higher electrical losses)

15 Monitoring of Switched Capacitor Bank Performance Switched capacitor banks are notorious for being out of service due to blown fuses, etc. Withtraditional traditional scheme, switched capacitor bank could be out of service for extended periods without operator knowing Losses higher if cap bank is out of service Routine inspections i needed? dd?

16 Traditional Voltage Regulation Strategy Line Drop Compensation accounts for varying load When load dthrough h voltage regulator is high, voltage drop along the feeder will be high LTC raises voltage to compensate This approach works well when all feeder load passes through h the voltage regulator LTC SUBSTATION Voltage Primary Feeder First Customer First Customer Distribution Transformer ANSI C84.1 Lower Limit (114 volts) Secondary 3 volts Primary 2 volts distribution transformer Service Drop Wires Last Customer Last Customer 1 volt secondary 1 volt service drop Distance

17 Voltage Regulation Problem When Large DG Unit is Introduced With a large DR out on the feeder, load through Vreg will be reduced Vreq thinks load is light on the feeder Vreg lowers tap setting to avoid light load, high voltage condition This action makes the actual heavy load, low voltage condition even worse DMS that accounts for DG affects can make the proper raise/lower decision based on total feeder conditions

18 Voltage Regulation During Alternate Feed Configuration Older style voltage regulators were often designed to handle a purely radial situation power flow always from the same direction (from the substation) Older style Vregs may not work correctly if power flow is from the opposite direction (see example) Could raise voltage when during light load, creating high voltage situation Could lower voltage when during heavy load, creating low voltage situation Feeder reconfiguration may become a more frequent occurrence due to Load transferred to another feeder during service restoration (FLISR) Optimal network reconfiguration to reduce losses (DMS application) Vreg not bi-directional Incorrect Operation!

19 Use of Bidirectional Voltage Regulator Can Use Bidirectional voltage regulator controller to handle feeder reconfiguration These make the opposite tap position movement when flow is from the reverse direction Vreg bi-directional Correct Operation!

20 Reverse Power Flow with DG A DG of sufficient size can reverse power flow Bidirectional Voltage Regulator may not work correctly DG does not typically provide a source strength stronger than the substation. Substation side voltage does not change, DG side changes Even with Bidirectional Vreg, could wind up lowering the voltage on a portion or the feeder during heavy load conditions Conclusion: Need a more sophisticated voltage control strategy when DG penetration is large enough to reverse power flow Normal Load Increased Load Vreg bi-directional Direction of Power Flow Vl Vs Direction of Power Flow 1.0 Vs.90 Vl Vl = Vs Vl = Vs x.90 DG DG Incorrect Operation!

21 Limitations of Traditional Volt VAR Control Current/Voltage Sensor Distribution Primary Line Capacitor Bank Current/Voltage Sensor Voltage Regulator "Local" Current/ Voltage Measurements Standalone Controller On/Off Control Command Signal "Local" Current/ Voltage Measurements Standalone Controller On/Off Control Command Signal The system is not continuously monitored The system lacks flexibility to respond to changing conditions out on the distribution feeders can misoperate following automatic reconfiguration System operation may not be optimal under all conditions Cannot override traditional operation during power system emergencies System may misoperate when modern grid devices (e.g., distributed generators) are present reverse power flow from DG can trick standalone controller to believe feeder has been reconfigured

22 Scorecard for Traditional Volt VAR Volt VAR Requirements Acceptable Voltage Profile Acceptable Power Factor Self Monitoring Operator Override Feeder Reconfiguration SmartGrid Devices Optimal Coordinated Control Selectable Operating Objectives Traditional Volt- VAR X X

23 SCADA Controlled Volt VAR VAR Volt VAR power apparatus monitored and controlled by Supervisory Control and Data Acquisition (SCADA) Volt VAR Control typically handled by two separate (independent) d systems: VAR Dispatch controls capacitor banks to improve power factor, reduce electrical losses, etc Voltage Control controls LTCs and/or voltage regulators to reduce demand and/or energy consumption (aka, Conservation Voltage Reduction) Operation of these systems is primarily based on a stored set of predetermined rules (e.g., if power factor is less than , then switch capacitor bank #1 off )

24 Overall Objective of VAR dispatch M

25 VAR Dispatch Components Switched & fixed feeder capacitor banks Capacitor bank control interface Communications facility one way paging or load management communications is sufficient Means of monitoring 3 phase var flow at the substation Master station running VAR dispatch software

26 Monitoring Real and Reactive Power Flow

27 VAR Dispatch Rules Applied

28 Real and Reactive Load Increases

29 Reactive Power Flow Exceeds Threshold

30 Capacitor Switched On

31 Change in Reactive Power Detected

32 Change in Reactive Power Detected Change detected by Substation RTU

33 Benefits of VAR Dispatch vs Traditional Self Monitoring Operator override capability Some improvement in efficiency

34 Objectives for SCADA Voltage Control Maintain acceptable voltage at all locations under all loading conditions Operate at as low as voltage as possible to reduce power consumption (aka Conservation Voltage Reduction)

35 Conservation Voltage Reduction Source: Tom Wilson PCS Utilidata

36 Benefits of Voltage Reduction for Various Types of Loads Constant impedance (power consumed is proportional to voltage squared) Incandescent lighting, resistive water heaters, stovetop and over cooking loads Constant power (demand is constant regardless of voltage) Electric motors, regulated power supplies Constant current (demand is proportional to voltage) (few of this type of load) Welding units, smelting, electroplating processes Feeder load is always a mix of the different load types Rules of thumb: 60/40 split (constant power/constant impedance) for summer peak loads 40/60 split for winter peak loads 80/20 for industrial areas 70/30 for residential load in residential with summer peaking 30/70 for res load with winter peaking Commercial loads: 50/50 or 60/40 Source: Power Distribution Planning Reference Book, H. Lee Willis

37 Benefits of Voltage Reduction Works best with resistive load (lighting and resistive heating) because power drawn decreases with the voltage squared. P = V 2 R Constant Impedance load Devices that operate using a thermostat generally do not reduce energy the devices just run longer

38 Benefits of Voltage Reduction Efficiency improve for small voltage reduction Incremental change in efficiency drops off and then turns negative as voltage is reduced Negative effect occurs sooner for heavily loaded motors

39 Benefits of Voltage Reduction on motors Motor loss reduction is a balancing act between magnetic effects and electrical effects: Magnetic losses (Iron Losses) are reduced when voltage is lowered Motor current increases as voltage is decreased (constant power effect) but if motor loading is light, current increases gradually Initial effect is reduced energy assumption, but as voltage is deceased further, copper loss increases and motor becomes less efficient Power Savings Obtained from Supply Voltage Variation on Squirrel Cage Induction Motors C. D. Pitis, BC Hydro Power Smart, and M. W. Zeller, BC Hydro Power Smart

40 Emerging Load Characteristics Digital Devices: Typically have a universal power supply covering a wide range of input voltage variations (e.g.: LCD/Plasma TV & VCRs = V) Constant power behavior Electric Vehicle Chargers: Constant power Constant Voltage (regulated output, during maintenance charge) Constant current (Low state of charge and fast charging type) NiMH Charging Profile Example charging curves for two EV chargers

41 Voltage Control Components EOF Voltage measurement 126V Actual Voltage 114V 116V CVR Cutoff EOF = End of feeder

42 EOF Voltage Below Voltage Control Threshold (No Control Actions) Voltage Control Processor Comm Interface EOF Voltage measurement 126V Actual Voltage Substation Transformer LTC Controller LTC Substation RTU OO OO OO Real Power (MW) Reactive Power (MVAR) Comm Interface Volt Meter or AMR 114V Voltage OO OO End of Feeder EOF = End of feeder Transformer 116V CVR Cutoff

43 EOF Voltage Above Voltage Control Threshold h Voltage Control Processor Comm Interface EOF Voltage measurement 126V Actual Voltage Substation Transformer LTC Controller LTC Substation RTU OO OO OO Comm Interface Volt Meter or AMR 114V OO OO End of Feeder EOF = End of feeder 116V CVR Cutoff

44 EOF Voltage Above Voltage Control Threshold (lower tap setting) Voltage Control Processor Comm Interface EOF Voltage measurement 126V Substation Transformer Lower Tap Setting LTC Controller LTC Substation RTU OO OO OO Comm Interface Volt Meter or AMR Actual Voltage 114V OO OO End of Feeder EOF = End of feeder 116V CVR Cutoff

45 EOF Voltage Above Voltage Control Threshold (lower tap setting) Voltage Control Processor Comm Interface EOF Voltage measurement 126V Substation Transformer Lower Tap Setting LTC Controller LTC Substation RTU OO OO OO Comm Interface Volt Meter or AMR OO OO Actual Voltage 114V End of Feeder 116V CVR Cutoff Self Monitoring Operator override capability CVR function not available with traditional

46 CVR based on Voltage measurements Hydro Quebec Results: Simple but not fully effective. Demonstration project gained only 30% of the estimated energy consumption. Volt meters not really at the end of the feeders. Volt meters installed only on 3 phases circuits. Targets need to cover also the worst case voltage drop of the single phase networks. Network topology during the demonstration project (1 year average) was not in its normal state 40% of the time. Substation Volt Meter End of Feeder Regulation controller Communication network Source: Volt-VAR Control Implementation at Hydro Québec ; Presented by Herve Delmas to IEEE Smart Distribution Volt Var Task Force, January 2010 A local regulation controller monitors the end of feeder s voltage and sets the tap to maintain this voltage at 115V.

47 Lack of Coordination between Volt and VAR control Switching a capacitor bank on raises the voltage, which: Increases no load losses in distribution transformers Increases energy consumption and possibly demand Lowering thevoltage through CVR: Makes the capacitor banks less effective (lower voltage means less capacitive current delivered by the cap banks)

48 SCADA Volt VAR Summary Does not adapt to changing feeder configuration (rules are fixed in advance) Does not adapt to varying operating needs (rules are fixed in advance) Overall efficiency is improved versus traditional approach, but is not necessarily optimal under all conditions Operation of VAR and Volt devices is not coordinated Does not adapt well to presence of modern grid devices such as DG

49 Sample Calc: kwh Loss Savings Due to VAR Dispatch Sample Calculation 2: Savings Due to kwh Reduction Input Values: Target power factor (TPF) = 1.00 useful Average power factor (AVGPF) =.95 Peak load on feeder (PKLOAD) = 8,000 kilowatts Distribution losses (% of peak load) = 4.0% Average cost to purchase one kilowatt-hour = 0.04 $/kwh formula Annual savings per feeder = 8760 x.456 x DLOSS x PKLOAD x (1 AVGPF 2 / TPF 2 ) x.04 kwh per year = 8760 x x 4% x 8000 x ( / 1.02) *.04 = $4,985 per year per feeder

50 Sample Calculation: Demand Reduction Due to VAR Dispatch Sample Calculation 3: Savings in Energy Supplier Demand Charges Input Values: Target power factor (TPF) = 1.00 Power factor at peak load (PKPF) =.98 Peak load on feeder (PKLOAD) = 8,000 kilowatts Energy supplier demand charge (DEMCHG) = 20 $/kw Annual savings per feeder useful formula = (1/PKPF - 1/TPF) x 100 % x PKLOAD x DMDCHG = (1 / / 1.00) x 100% x 8,000 x 20 = $3,265 per year per feeder

51 Volt VAR Scorecard Volt-VAR Approach Volt VAR Requirements Traditional Volt- VAR SCADA Volt- VAR Acceptable Voltage Profile X X Acceptable Power Factor X X Self Monitoring X Operator Override X Feeder Reconfiguration SmartGrid Devices Optimal Coordinated Control Selectable Operating Objectives

52 Volt VAR Optimization (Centralized Approach) Develops and executes a coordinated optimal switching plan for all voltage control devices Uses optimal power flowprogram to decide what to do Achieves utility specified objective functions: Minimize distribution system power loss Minimize power demand (sum of distribution power loss and customer demand) Maximize revenue (the difference between energy sales and energy prime cost) Combination of the above Can bias the results to minimize tap changer movement and other equipment control actions that put additional i wear and tear on the physical equipment

53 Modeling Load Voltage Sensitivity Accurate load model for IVVC: Determine appropriate values for coefficients on above formula using field experiments and regression analysis

54 Volt VAR Optimization (VVO) System Configuration i Temp Changes AMI MDMS Line Switch Geographic Information System (GIS) Perm Changes Distribution System Model Dynamic Changes Switched Cap Bank On-Line Power Flow (OLPF) Distribution SCADA Develops a coordinated optimal switching plan for all voltage control devices and executes the plan IVVC Optimizing Engine Substation Transformer with TCUL Substation RTU Line Voltage Regulator Substation Capacitor Bank

55 Volt VAR Optimization (VVO) System Operation Voltage Feedback, Accurate load data Switch Status Temp Changes AMI MDMS Line Switch Bank voltage & status, switch control Geographic Information System (GIS) Perm Changes Distribution System Model Dynamic Changes Switched Cap Bank IVVC requires realtime monitoring & control of sub & feeder devices On-Line Power Flow (OLPF) IVVC Optimizing Engine Distribution SCADA Line Voltage Regulator Monitor & control tap position, measure load voltage and load Substation Transformer with TCUL Substation RTU Substation Capacitor Bank Monitor & control tap position, measure load voltage and load Bank voltage & status, switch control

56 Volt VAR Optimization (VVO) System Operation Cuts, jumpers, manual switching Temp Changes AMI Real-Time Updates MDMS Line Switch Geographic Information System (GIS) Perm Changes Distribution System Model Dynamic Changes Switched Cap Bank Permanent asset changes (line extension, reconductor) On-Line Power Flow (OLPF) Distribution SCADA IVVC Optimizing Engine Line Voltage Regulator IVVC requires an accurate, up-to date electrical model Substation Transformer with TCUL Substation RTU Substation Capacitor Bank

57 Volt VAR Optimization (VVO) System Operation Temp Changes AMI MDMS Line Switch Geographic Information System (GIS) Perm Changes Distribution System Model Dynamic Changes Switched Cap Bank OLPF calculates losses, voltage profile, etc On-Line Power Flow (OLPF) Distribution SCADA IVVC Optimizing Engine Line Voltage Regulator Powerflow Results Substation RTU Substation Transformer with TCUL Substation Capacitor Bank

58 Volt VAR Optimization (VVO) System Operation Temp Changes AMI MDMS Line Switch Geographic Information System (GIS) Perm Changes Distribution System Model Dynamic Changes Switched Cap Bank Determines optimal set of control actions to achieve a desired objective On-Line Power Flow (OLPF) Distribution SCADA IVVC Optimizing Engine Line Voltage Regulator Powerflow Results Substation RTU Alternative Switching Plan Substation Transformer with TCUL Substation Capacitor Bank

59 Volt VAR Optimization (VVO) System Operation Temp Changes AMI MDMS Line Switch Geographic Information System (GIS) Perm Changes Distribution System Model Dynamic Changes Switched Cap Bank Determines optimal set of control actions to achieve a desired objective On-Line Power Flow (OLPF) Distribution SCADA IVVC Optimizing Engine Line Voltage Regulator Substation RTU Optimal Switching Plan Substation Transformer with TCUL Substation Capacitor Bank

60 Impact of Voltage Reduction on Customers In most cases, voltage reduction does not impact customer equipment, but.. Some customers are aware of the principle p of voltage reduction and gave already taken steps to lower their voltage via individual service voltage regulators (e.g. Smart motor controllers) When utility lowers the voltage on the feeder, customers who are already lowering their own voltage will go below the minimum

61 Voltage Reduction Limitations Feeders voltage limited? May not be able to reduce voltage at all May need to flatten the voltage profile (Progress energy, Georgia Power, etc)

62 Current Technologies, LLC

63 Time Decay of CVR Effects The most reduction occurs right when the voltage is reduced and then some of the reduction is lost as some loadsjust run longer

64 IVVC Benefits Dynamic model dlupdates dt automatically ti when reconfiguration occurs Volt VAR control actions are coordinated System can model the effects of Distributed Generation and other modern grid elements Produces optimal results Accommodates varying operating objectives depending di on present need

65 Benefits of Volt VAR Optimization CVR Factor = ΔP / ΔV basic on actual CVR experience: BC Hd Hydro CVR f = Progress Energy CVR f = 0.8 Georgia Power CVR f = Annual Energy Savings = Average Load x #Hours per year x % voltage reduction x CVRf x value of energy conservation Lost revenue from kwh sales CVR performed during peak load period can be viewed as demand (capacity) reduction

66 Final Volt VAR VAR Scorecard Volt-VAR VAR Approach Volt VAR Requirements Traditional Volt- VAR SCADA Volt- VAR Integrated Volt- VAR Acceptable Voltage Profile X X X Acceptable Power Factor X X X Self Monitoring X X Operator Override X X Feeder Reconfiguration X SmartGrid Devices X Optimal Coordinated Control X Selectable Operating Objectives X

67 Volt VAR Optimization Next Steps PV Inverter PV Inverter SUBSTATION Supplementary Regulators Supplementary Regulators Rotating DG FEEDER LTC Control Rotating DG PV Inverter PF Capacit or Capacitor Control Rotating DG Rotating DG PV Inverter Communication Link Voltage and VAR Regulation Coordination Algorithm Manages tap changer settings, inverter and rotating machine VAR levels, and capacitors to regulate voltage, reduce losses, conserve energy, and system resources

68 Feeder Flow and Resource Control (DG+ES) ES DR Utility grid DG ΔP G RES Constant power flow or firming up rate of change at PCC Eliminate adverse impact Reducereserve capacity requirement ΔP W