2 INTERMOUNTAIN POWER PROJECT STABILITY ENHANCEMENT (IPPSE) SYSTEM Presented by:Ken Silver-Electrical Service Manager (Manager of Energy Control and Extra High Voltage Stations )Travis Smith-Assistant Manager (Manager of Intermountain Converter Station)Brian Cast–Electrical Engineer (Grid Operation and Energy Prescheduling Supervisor )Ken Lindquist – System Protection EngineerAttendees:Ken Silver, Mukhlesur Bhuiyan, Travis Smith, Tom Snyder, Brian Cast, Saif Mogri, Ken Lindquist, Carlos Garay and John HuChuck Wu (On Phone)
3 Agenda System Overview – Ken Silver Performance and Operational History – Travis SmithSystem Studies – Ken LindquistSystem Design – Travis SmithArming Function – Brian CastOperation and Monitoring – Brian CastOperating Procedures for Abnormal Conditions - Ken SilverCommissioning, Maintenance, and Testing – Travis SmithConclusions – Travis Smith
5 1. System OverviewThe Purpose of Intermountain Power Project Stability Enhancement (IPPSE) is to ensure WECC system stability after outages to the Intermountain Power Project DC system (IPPDC). This is achieved by arming predetermined remedial actions prior to the occurrence of a disturbance associated with the IPPDC.Due to IPPDC system upgrade from 1920MW to 2400MW, the IPPSE is submitted for review.
6 1. System Overview Remedial Actions Required: The Intermountain Power Project (IPP) Contingency Arming System (CAS)has been implemented to mitigate IPPDC disturbances by tripping one or twoIPP generating units. The IPP CAS has been in operation since Thedesign and operations of this RAS has been reported to WECC on April 1986with a report entitled “Intermountain Power Project Contingency ArmingSystem: One Unit Operation” and on August 1992, with a report entitled“Intermountain Power Project Contingency Arming System: Non-Credibilityof Remedial Action Scheme Failure.”Formal Operating Procedure:The IPP CAS consists of arming-charts where real-time power output of theIPP generating units and the IPPDC line flows are used to select the no-unit,one-unit or two-unit arming of remedial actions. The IPP CAS and associatedoperating procedures are included with the LADWP’s Energy Control CenterEnergy Management System (ECC-EMS) computers.
12 2. Performance and Operational History The existing IPPSE was installed May 10, 1986A design criteria of one operational failure in 3 years was used.How have we done ?
13 2. Performance and Operational History In 24 years there have been 28 actions. Seventeen of which occurred prior to August 1992.There have been 6 failures 5 of which occurred prior to August 1992.The system did not achieve its goal from 1986 to However from 1992 to the present, the system has achieved its goals.
14 2. Performance and Operational History What Changed in 1992?A problem with the Monopolar Out signal was discovered and corrected.A design change was initiated to allow for 1 restart in Monopolar Operation.
15 2. Performance and Operational History SuccessAfter the modifications, the system operated correctly.
17 3. Study Process SummaryCo-ordinate with Impacted System Operators (PacifiCorp) in preparing study plan and study conditions.Determine Impact on the WECC System.Determine Maximum “IPP Net Import” Capability.Determine Generation Tripping delay times.Determine IPP Contingency Arming Scheme (CAS) Operational Nomograms.
18 3. System Condition Studied IPP DC Upgrade This is just a simple overview of the IPP STS DC Line and AC connections at Delta, Utah.
19 Stressed TOT2 to Path Rating 3. Utah South Conditions"Utah South" is most sensitive to the impact of IPP DC. The TOT2B and TOT2C paths were the main focus of this study and stressed to there path rating of 800(TOT2C) and 300(Path2B) throughout this study.TOT2BStressed TOT2 to Path RatingTOT2C
20 3. “Net IPP Import” Sensitivity (Post-Transient Power Flow) Results from the studies reveals that for the loss of IPPDC Bipole, the system is sensitive to the "import", the IPP operation will be limited to 2400MW DC on the STS with import of 600MW (measured at IPP) * IPP DC Will Operate with Maximum “Net IPP Import” of 600MW – Limited by Line Overload
21 3. Determine Delay Generation Tripping DC Fault Restart1st2nd3rdDeionization Time (ms)225325425Deionization Time (cycles)13.519.525.5Cumulative (cycles)3358.5Simulate CAS time (cycles) (trip unit)184070Accommodate possible DC restart sequence after a DC fault;To lessen the stress by possibly using a less stressful turbine or boiler trip.Generator TrippingMethodsTime to0 OutputCommentsElectrical Trip< 10 CyclesMost Stressful on boilersand turbinesBoiler Trip~ 42 Seconds15 second Delay20 seconds to 100MW,6 second to breaker OpenTurbine Trip~ 23 Seconds15 second delay,2 seconds to 100MW,6 seconds to breaker OpenThis slide shows the timing characteristics of the HVDC controls DC Line Fault Protection.The studies show that a tripping action needs to occur in the 1st 60 cycles of the event. The 1st line protection restart is accomplished in 18 cycles. However the time to do both the 1st & 2nd, at 40 cycles, is too close to the limit of 60 cycles. Therefore if the 1st restart does not clear the DC Line fault and restore normal power flow a trip signal will be sent.
22 3. Stability Plot for Loss of Bipole with Restart (for DC Fault Only) (Worst Stressed Condition) Trip 1 Unit after First Restart Failed and Second Unit after the Second Restart FailedTrip Both Units after First Restart FailedHere we see the study results showing that if we wait for the second DC Line Protection action the AC Voltage dip exceeds the criteria.* CAS Will Trip Units after 1 Restart Attempt Failed
23 3. Stability Plot for Loss of Bipole with Delayed CAS Generation Tripping for Lower IPP DC Schedule IPP DC Schedule 1500MWIPP DC Schedule 1400MWHere we show that when the total DC power transmitted is at or less than 1400 MW stability is not an issue. There is more time to allow a ‘softer’ trip of the generators. This a turbine or boiler trip depending on arming.The charts show that there is more time before a trip needs to occur and the system swing is less.* CAS Will Delay Generation Tripping for IPP DC Schedule 1400MW or Less
24 3. Delayed CAS Generation Tripping for Loss of 1 Pole Short Term Overload Capability of IPP DCLoss of Bipole is only possible for simultaneous DC faults or disastrous DC Controls failure.AC faults will result in the loss of 1 pole. This chart is here to show the overload capability of the STS HVDC. If there is a loss of one pole when operating in Bipolar mode there is an automatic increase of power on the remaining pole up to 1600MW DC. Then both the IPP generation and HVDC ramp down to the maximum pole rating, 1200MW, over a controlled 7 minute ramp. This feature helps to minimize the shock to the AC network.
25 3. Delayed CAS Generation Tripping for Loss of 1 Pole (IPP AC Fault Trip 1 Unit + MWC Generations) No RASDelayed TrippingFast TrippingHere we are looking at the effects of the STS HVDC in Bipolar operation and the event is losing one of the poles.1st chart shows that stability is not an issue.2nd chart shows that allowing a boiler or turbine trip, a delayed trip, there is less impact to the AC system.3rd chart shows that an electrical trip results in larger swings that the remaining generator is exposed to.* CAS Will Delay Generation Tripping for Loss of 1 Pole
26 3. IPP CAS Generation Tripping Level Operating Nomogram for Bipole Operation for the Loss of Bipole Chart on the left, each dot represents a separate case that was run.The limitation found is the post-transient current flow at the Sigurd-Three Peaks location.The right hand chart is the nomogram developed from the study results.
27 3. IPP CAS Generation Tripping Level Operating Nomogram for Bipole Operation for the Loss of 1 Pole For Bipole operation and the loss of one pole the limitation is the post-transient voltage deviation at Abajo 69KV bus.Nomogram developed from the studies is again on the right.
28 3. IPP CAS Generation Tripping Level Operating Nomogram for Mono-pole Operation for the Loss of 1 Pole(Just in case people ask about restrictive nomogram for mono-polar operation. Voltage deviation N-1 criteria is 5% while N-2 is 10%. )The other normal operating mode for the STS HVDC is to have only one pole in operation.Here the limitation is the post-transient current flow at Sigurd-Three PeaksAND the voltage deviation of 5% at Abajo. And the nomogram to the right.This concludes the studies presentation.
29 3. Study SummaryIPP DC limited to net AC Import capability of 600MW under maximum Utah South export conditionsCAS will Trip Units after 1 Restart Attempt FailedCAS will Delay Generation Tripping for IPP DC Schedule 1400MW or LessCAS will Delay Generation Tripping for Loss of 1 Pole - Limited by Voltage DeviationsIn summary:The thermal line overload is when 2400MW with 600 MW of import.Action will be initiated if the 1st line protection restart is not successful.When the STS is operating at or below 1400MW a delayed trip is allowed.The loss of one pole with a delayed trip also meets all criteria.
31 4. System DesignDesign PhilosophyMeet the System Studies GuidelinesInsure RedundancyReduce the HardwareCentralize the Logic
32 Only 1 operational failure in 3 years is allowed. 4. System DesignFollowing the guidelines established by the system studies were the driving force in the design of the IPPSE.All parameters of the studies have been met which also allowed for a simpler more efficient design.Only 1 operational failure in 3 years is allowed.
34 4. System DesignThe Bipole Controls are a completely redundant Mach 2 Control System designed by ABB.All protection actions are routed through this control system.The IPPSE Logic is fully contained in this system thus reducing the system hardware requirements.All remedial outputs are generated from this control system.
35 4. System DesignThe remedials from the IPPSE Logic have been simplified into two outputs.Monopolar OutBipolar OutBased on these two signals and the Nomograms, all IPPSE actions are appropriately taken.
37 IPP Digital Microwave System 4. System DesignIPP Digital Microwave SystemOriginal analog system installed 1985System was replaced with Harris Stratex (now Aviat Networks) digital microwave radios in 2004LADWP operated and maintained
38 IPP Microwave Power Redundancy 4. System DesignIPP Microwave Power RedundancyPropane Back up Generators24 VDC Power Plants
41 5. Arming Function Overview: Arming is automated by an application running in LADWP’s energy management system.Nomograms, called “charts”, specify the arming level.Each chart has a series of curves that provide arming levels as a function of IPP net generation (including Milford generation) and the DC line flow.The application selects charts based on monitored power system conditions and the specific trigger being armed.
42 5. Arming Function Charts: One curve per remedial action. Arming is a function of net gen vs. DC flow.Top-most curve provides DC flow limit.Added remedial actions will require an increase in the number of curves per chart.
43 5. Arming Function Chart Sets: There may be up to five triggers for remedial actions.Each trigger has its own arming for remedial action.Therefore, there is one chart per trigger.The set of charts for the triggers is a “chart set”.
44 5. Arming Function Chart Set Selection: There are multiple chart sets to accommodate varying system conditions.Chart sets are functionally organized into rows and columns.Columns are selected based on monitored line flows.Rows are selected based on line outages and IPP operating modes.
45 5. Arming Function Chart Set Selection (cont’d): Original design provided for 24 columns.Although they no longer affect arming, three power flows are still monitored: Pacific AC Intertie, Arizona–California, and Utah South.The system study indicates nomogram sensitivity to Utah South power flow, so use of multiple columns may become necessary.
46 5. Arming Function Imports: Chart shows a 600-MW import limit. IPP AC lines have 1317-MW import capability.Chart is worst-case scenario.Other cases allow more imports.
47 5. Arming Function Import Example: A 72-MW on Sigurd–Three Peak may allow a 400-MW in imports.This can be implemented via multiple columns or via dynamic shifting of affected curves.
48 5. Arming Function Summary of Arming Function Changes: Increase in the number of curves per chart due to increase in number of remedial actions.Decrease in the number of charts per chart set due to decrease in the number of triggers.Increase in the number of chart set columns and/or addition of dynamic curve adjustments due to varying AC import limits depending on Utah South flow.
50 6. Monitoring and Operation Overview:LADWP’s Energy Control Center (ECC) and IPP both have monitoring capability.The arming application runs at the ECC, but either site can arm manually.Except for automatic arming, the RAS operation occurs entirely at IPP, but is monitored by both sites.The slides that follow show monitoring and operation as seen at the ECC.
51 6. Monitoring and Operation The interface at the ECC includes the following displays:Curves & DC LimitsColumns & ChartsPanel Status (i.e. RAS Status)AnnunciatorsThese displays are summarized and shown in the slides that follow.
52 6. Monitoring and Operation Curves & DC Limits:Shows summary data in upper-right corner.Provides for viewing and update of curves and charts.Shows remedial action selected for each active chart.Shows DC limits from charts and other nomograms.
53 6. Monitoring and Operation Curves & DC Limits Display
54 6. Monitoring and Operation Changes to Curves & DC Limits:System studies do not show a need for separate nomograms for DC limits from Utah North, Utah South, or Northeast/Southeast flows.DC limit for power flows flow will be inherent in the contingency arming limit from the selected charts.Dynamic offsets to curve data, when implemented, will be shown on this display.
55 6. Monitoring and Operation Columns & Charts:Shows power flows for chart set column selection.Shows line status.Shows plant operating mode.Shows column and chart set selection in the summary data in the upper-right corner.
56 6. Monitoring and Operation Columns & Charts Display
57 6. Monitoring and Operation Changes to Columns & DC Charts:Column selection is no longer influenced by Pacific AC Intertie and Arizona–California flows.Additional columns may be needed to model the effects of Utah South flow on AC import capability.
58 6. Monitoring and Operation Panel Status:The RAS is currently implemented at IPP via redundant hardware systems called “panels”.Each arming control point is wired to operate both panels from a single control operation.Each panel independently reports its status.Arming controls can be issued via the arming application or manually via SCADA control actions.
59 6. Monitoring and Operation Panel Status (cont’d):Provides a control and pair of state indications for each combination of trigger and remedial action that may be armed.Provides for manual entry of an arming pattern when in MANUAL mode and shows the application-determined arming pattern when in AUTOMATIC mode.Shows panel status values.Shows triggers actuated. When a trigger is actuated, the RAS will execute any remedial actions armed for that trigger.
60 6. Monitoring and Operation Panel Status Display
61 6. Monitoring and Operation Changes to Panel Status:The application currently implements the arming matrix by using an obscure feature to control multiple arming state points with a single control operation. (This is much quicker than using time-consuming discrete control actions for each arming state point.)This set of arming state points to specify remedial actions for each trigger will be replaced with a single analog point for each trigger that specifies the remedial actions to execute.The RAS implementation will be part of the DC control system.
62 6. Monitoring and Operation Annunciator Displays:The RAS trigger inputs are actually aggregations of multiple triggering inputs from relay and DC control systems.For this reason, the RAS trigger inputs are in some places called “super triggers”.The annunciator displays show each trigger input and identify the super triggers that it activates.
63 6. Monitoring and Operation Annunciator Display 1
64 6. Monitoring and Operation Annunciator Display 2
65 6. Monitoring and Operation Annunciator Changes:According to system studies, many of the triggering inputs will no longer require remedial actions.Only triggering inputs for monopole and bipole blocks will continue to be relevant.The number of super triggers needed will reduce from five to two.The triggering inputs no longer requiring remedial action may be retained on the annunciator displays for reference.
66 6. Monitoring and Operation Summary of Monitoring and Operation Changes:The RAS function will be located in the DC control system.Arming will be specified via analog arming levels rather than discrete digital states.Arming may use real-time power flow to bias affected nomogram curves.Additional remedial actions are being added.The inputs that affect remedial action arming and execution are being updated according to study results.
67 7. Operating Procedure for Abnormal SystemConditions
68 7. Operating Procedures for Abnormal System Conditions The RAS operates incorrectly (failure to operate or false operation)As soon as the IPPSE has failed or operated improperly, generation and DC flows will be curtailed to a point where remedial action is not required. The condition will be maintained until repairs can be made or the RAS is proven to be stable.
69 7. Operating Procedures for Abnormal System Conditions One part of a redundant RAS system is unavailable so that complete redundancy is no longer assuredPersonnel will be dispatched immediately to work on the unavailable system to restore it to operational status as soon as possible. Curtailment is not required in this condition.
70 7. Operating Procedures for Abnormal System Conditions When unscheduled, or unplanned and not coordinated, unavailability of the subject RAS (complete loss of RAS) impacts operationGeneration and DC flows will be curtailed to a point where RAS is not required or until such time as the RAS becomes available again.
71 7. Operating Procedures for Abnormal System Conditions When a partial or total loss of input data required for arming decisionsAll input data required for arming originates from Intermountain Converter Station (ICS) and Intermountain Generating Station (IGS). The ICS operator will manually set the proper arming as directed by the Energy Control Center (ECC). The ICS operator has the ability to determine and set proper arming independent of ECC.
73 8. Commissioning, Maintenance, and Testing Testing of the IPPSE Logic will begin during the Factory Acceptance Tests in Sweden. This will begin in May 2010.Commissioning of the new system will begin in October of 2010 when the first Mach 2 control comes on line.The IPPSE system will be fully operational by Mid December 2010.
74 8. Commissioning, Maintenance, and Testing All critical components such as communication links, test switches and computers are monitored by the new Alarm Reporting and Monitoring System (ARMS)Emergency maintenance can be done on line without degrading the system. Only redundancy will be lost.Scheduled Maintenance is every 2 years.
75 8. Commissioning, Maintenance, and Testing Testing will be “End to End”, from ECC to the Generator and Milford Intermountain Line 1 Blocking Switches.Each arming level in the Nomograms will be tested to assure that the proper remedial is sent to the blocking switch.All intermediate signals, remedial outputs and trip signals will be recorded for analysis.
77 System Studies Guidelines 9. ConclusionsSystem Studies GuidelinesSystem studies were extensive and the results were incorporated into the system design.All system hardware and software is monitored for correct operation.
78 Redundancy 9. Conclusions All Protections, Control Systems, Communication Systems and Monitoring Systems are completely redundant.
79 Reduce and Simplify the Hardware 9. ConclusionsReduce and Simplify the HardwareThe input triggers have been reduced from 19 to 2.The Nomograms have been reduced from 38 to 3.
80 Centralize the Logic 9. Conclusions All IPPSE Logic is now contained in the HVDC Mach 2 control system.
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