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Voltage Workshop Agenda (http://www.ercot.com/calendar/2015/4/7/57909) ERCOT Austin Room 206 7620 Metro Center Drive Austin, Texas 78744 Tuesday, April 7, 2015 / 1:00 p.m. – 4:00 p.m. WebEx Conference Teleconference: 877-668-4493 Meeting number: 652 660 765 Meeting password: vws0407 (Note: When logging into WebEx, please make note of your Personal Identification Number (PIN)) 1. Antitrust Admonition

S. Solis (ERCOT) 1:00 p.m.

2. Introductions


3. Voltage Planning and Coordination Overview


4. ERCOT System Planning for Voltage

S. Borkar (ERCOT) 1:45 p.m.

5. Break

All 2:30 p.m.

6. TSP System Planning for Voltage

J. Santos (Garland) 2:45 p.m.

7. Day 1 Wrap up/Discussion/Q&A


8. Adjourn 4:00 p.m.

Voltage Workshop Agenda (http://www.ercot.com/calendar/2015/4/8/57913) ERCOT Austin Room 206 7620 Metro Center Drive Austin, Texas 78744 Wednesday, April 8, 2015 / 8:30 a.m. – 3:30 p.m. WebEx Conference Teleconference: 877-668-4493 Meeting number: 653 015 474 Meeting password: vws0408 (Note: When logging into WebEx, please make note of your Personal Identification Number (PIN)) 1. Antitrust Admonition

S. Solis (ERCOT) 8:30 a.m.

2. Seasonal Voltage Profiles - ERCOT

B. Blevins (ERCOT) 8:35 a.m.

3. 4.

Seasonal Voltage Profiles – ERCOT TO Break

L. Rodriguez (AEP) All

9:20 a.m. 10:05a.m.

5. Outage Coordination - ERCOT

A. Lee (ERCOT)

10:15a.m.

6. Outage Coordination – ERCOT TO

D. Marr (LCRA) 10:45 a.m.

7. ERCOT Operations for Voltage - Next Day/Current Day - Current Day/Real Time

Lunch

C. Thompson (ERCOT) J. Hartmann (ERCOT) All

11:15 a.m. 11:30 a.m. 12:00 a.m.

8. 9.

ERCOT Resource Entity Voltage Coordination ERCOT TO Operations for Voltage

- Next Day/Current Day - Current Day/Real Time

S. Rake (Luminant) S. Morris (TNMP) S. Williams (ONCOR) K. Sills (ONCOR)

1:00 p.m. 1:30 p.m. 2:00 p.m.

10.

Break

All

2:45 p.m.

11. Summary Exit Presentation / Discussion/Q&A

S. Solis (ERCOT); All 3:00 p.m.

12. Adjourn 3:30 p.m.

Voltage Planning and Coordination OverviewStephen SolisSystem Operations Improvement Manager

Voltage WorkshopApril 7, 2015

Outline

• Voltage Workshop Objective

• Time Horizons and Processes

• Coordination

• Modeling

• Notable Issues

2

Voltage Workshop Objective

• Broad understanding of the various processes, entities, and issues related to voltage coordination.

• Robust discussion from diverse viewpoints

• List of issues to be grouped and addressed in future NPRRs, NOGRRs, PGRRs, and SCRs.– Note: Focus is on steady state voltage (UVLS,

transient, thermal, etc. not focus)

3

Time Horizons

Planning

Long Term Planning ( 5 to 10 years)

Near Term Planning (1 to 5 years)

Operations Planning

Seasonal (up to 1 year)

Outage Coordination (3 to 90 days)

Next / Current Day

Next Day

Current Day (1 hour up to several hours in future)

4

ERCOT Processes Overview

Regional Transmission

Plan

Long-Term System

Assessment

Regional Planning Group

Assessments

Generator Interconnection

Studies

Voltage Stability Screening Studies

Seasonal Voltage Profile studies

Outage Coordination

Studies (90, 45, 9, 3 days)

Next Day Study

Daily Reliability Unit Commitment

(DRUC)

Current Day Future Studies

Hourly Reliability Unit Commitment

(HRUC)

Ad Hoc Future Studies

Real Time Contingency

Analysis (RTCA)

Voltage Security Assessment Tool

(VSAT)

Ad Hoc Real Time Studies

Constraint Management Plan

Annual Review

Reliability Must Run (RMR)

studies

5

Generic Process Description

6

What do they accomplish?

• All of the processes support having a plan to be able to operate within voltage limits both pre contingency and post contingency and without any steady state voltage instability in real time.

7

ERCOT Planning Processes• Coordination between ERCOT

and TSPs

• Steady State Working Group(SSWG) cases utilized

• All Facilities in service

• ERCOT Presentation– Sandeep Borkar

8

ERCOT Seasonal Assessments

• Coordination between ERCOT and TSPs

• SSWG cases utilized• RMR assessments conducted if a

notice for suspension of operations is received from a resource.

• Annual verification of Constraint Management Plans prior to summer peak

• ERCOT Presentation– Bill Blevins

Seasonal Voltage Profile studies

Constraint Management Plan

Annual Review

Reliability Must Run (RMR)

studies

9

ERCOT Outage Coordination Assessments

• ERCOT performs steady state analysis in advance (90 days, 45 days, 9 day, and 3 days)

• Network Operations Model case

• Coordination between ERCOT and TSPs as necessary

• ERCOT Presentation:– Alex Lee

10

Next Day Assessments• ERCOT performs a “Next Day”

steady state analysis


• RUC identifies any capacity needed for operation under G

• ERCOT Presentation:– Chad Thompson

Next Day Study

Daily Reliability Unit Commitment

(DRUC)

11

Current Day Assessments

• ERCOT performs future looking studies at various times to assess peak conditions.


• Hourly RUC identifies any capacity needed for operation under GTLs.

• ERCOT Presentation:– Jimmy Hartmann

– Chad Thompson12

Real Time Studies• Real Time Contingency Analysis

runs steady state analysis with State Estimator data on the Network Operations Model.

• Voltage Security Assessment Tool (VSAT) runs voltage stability analysis on select load pockets

• Additional offline Steady State Analysis is conducted as needed.

• ERCOT Presentation– Jimmy Hartmann– Chad Thompson

Real Time Contingency

Analysis (RTCA)

Voltage Security Assessment Tool

(VSAT)

Ad Hoc Real Time Studies

13

Elements of Coordination• Voltage Profile Group consists of ERCOT,

TSPs, and Resource Entities

• SSWG cases consist of ERCOT and TSPs efforts.

• Outages are coordinated between ERCOT and TSPs

• CMPs are coordinated between ERCOT, TSPs, and QSE if necessary.

14

Modeling• Voltage Schedules

– SSWG cases have utilized generic voltage schedules in the past.

– ERCOT currently utilizes voltage schedules modeled after operational data for Outage Coordination studies up to Real Time.

– Future SSWG cases will have the more detailed voltage schedules that ERCOT has modeled.

– If a TSP wants to utilize a different voltage schedule, then a PMCR must be created.

15

Modeling• Voltage Limits

– TSPs provide voltage limits for the operations horizon through the Network Operations Model (NOMCR).

– TSPs can provide different voltage limits for the planning horizon through a PMCR in the SSWG process.

• Some TSPs have chosen to utilize the default voltage limits identified in the ERCOT SOL Methodology.

16

Modeling• Resource Reactive Capability

– Resources provide their reactive capability through the Resource Asset Registration Form (RARF).

– Resources are periodically tested to verify their reactive capability.

• ERCOT utilizes State Estimator on all buses

– Allows ERCOT to have values for voltage where no telemetry exists.

– Additional telemetry can improve SE performance

17

Examples of challenges• Sizing of Reactive Devices in planning may

cause operational challenges to maintain voltage limits.

• Limits in planning vary between TSPs affecting neighbors.

• Planning cases and simulations may not represent issues that may occur due to generation dispatch variances.

• Corrective actions for 69kV voltage exceedances may be on Distribution System

18

Examples of challenges• Voltage Profile/set point terminology has

different interpretations as to the on peak/off peak as both a range and two separate set points with a threshold.

• SSWG cases may have planning horizon voltage limits and schedules that differ from operations.

• ERCOT TO authority to direct voltage set points for generators has been challenged at times.

19

Questions?

20

Voltage Workshop ERCOT Planning: Steady State

Sandeep Borkar ERCOT Transmission Planning

April 2015

2

Outline

• ERCOT Transmission planning overview

• Regional Transmission Planning-Voltage Considerations

• Voltage stability assessments

3

ERCOT Transmission Planning

Steady State

Regional Assessments

RPG project reviews

Resource Integration

Dynamic

Voltage and Dynamic stability

assessments

ERCOT Transmission Planning Overview

4

ERCOT Transmission Planning Overview

Regional Assessments

Near-term assessment

(RTP)

Long-term assessment

(LTSA)

• Assess the reliability needs of ERCOT system per standards and regulations (NERC TPL-001-4, ERCOT Planning Guides, ERCOT Nodal Protocols)

• RTP: Identify corrective action plans for potential criteria violations in the near-term

• LTSA: Identify conceptual projects based on long-term needs across diverse scenarios

5

RTP Reliability Analysis Overview

Case Preparation

• Initial case: Latest SSWG Data Set B (DSB) case• Update generation and load assumptions based on the RTP

Scope• TP provided voltage limits are retained from the SSWG

cases, unless these limits are less binding than one established in ERCOT SOL Methodology

Reliability Analysis

• Single event SCOPF and Contingency Analysis using contingencies defined per the TPL-001-4

• Multiple element contingency analysis including G-1+N-1 and X-1+N-1

• Resolve thermal overloads and address voltage criteria violations (this includes violation of high or low bus voltages limit and post contingency deviation limits)

6

RTP Process overview• Input assumptions that impact voltage analysis

– Voltage limits modeled as per System Operating Limit (SOL) methodology

– Flexible AC transmission system (FACTS) devices not operated to provide steady state voltage control are modeled out-of-service

– FACTS devices available for voltage control are modeled as switched-shunt with discreet set points or generators on AVR

• Reliability analysis– Starts with N-1, G-1+N-1 and X-1+N-1 contingency analysis

using an AC SCOPF

– Resolve thermal violations with transmission upgrades or additions

– Voltage violations are addressed at the end of reliability analysis

– Sensitivity cases with no wind generation are studied

7

Contingency Definitions and Performance Requirement

Category Initial Condition Event

Load Shedding allowed? Category

under Old TPL> 300 kV <= 300

kVP0 System intact None N N Cat A

P1-1

System intact

G-1 (generator) N N Cat B1P1-2 T-1 (transmission) N N Cat B2P1-3 X-1 (transformer) N N Cat B3P1-4 S-1 (Shunt device including FACTS devices that are connected to ground) N NP1-5 DC N N Cat B4P2-1

System intact

Open Line (one-end of the line) W/O Fault N NP2-2 BS (Bus section fault) N Y Cat C1P2-3 NBTB (Internal failure of non-bus tie breaker) N Y Cat C2P2-4 BTB (Internal failure of bus tie breaker) Y Y Cat C2P3-1

G-1 + System Adjustment

G-1 (generator) N N

Cat C3

P3-2 T-1 (transmission) N NP3-3 X-1 (transformer) N NP3-4 S-1 (Shunt device including FACTS devices that are connected to ground) N NP3-5 DC N NP4-1

System intactStuck Breaker of non-bus-tie breaker (NBTB) for the fault associated with

G-1 N Y Cat C6P4-2 T-1 N Y Cat C7P4-3 X-1 N Y Cat C8P4-4 S-1 N YP4-5 BS N Y Cat C9P4-6 Stuck Breaker of bus-tie breaker (BTB) for the fault associated with BS Y Cat C9P5-1

System intact Failure of non-redundant relay for the fault associated with

G-1 N Y Cat C6P5-2 T-1 N Y Cat C7P5-3 X-1 N Y Cat C8P5-4 S-1 N YP5-5 BS N Y Cat C9P6-1

N-1 + Adjustment

T-1 (transmission) Y Y

Cat C3P6-2 X-1 (transformer) Y YP6-3 S-1 (Shunt device including FACTS devices that are connected to ground) Y YP6-4 DC Y YP7-1 System intact Two adjacent circuits on common structure. (exclude if 1 mile or less) Y Y Cat C5P7-2 Loss of a bipolar DC Y Y Cat C4

8

SOL Methodology

• Per the ERCOT SOL Methodology (Planning steady state voltage limit)– 0.95 per unit to 1.05 per unit in the pre-contingency state (P0)

– 0.90 per unit to 1.05 per unit in the post-contingency state (P1 through P7)

• TP/TO provided limits (more or less restrictive than the above limits) are retained from SSWG case

• SSWG case starts with the operations voltage limits and schedules as a default. TP can update limits specific to planning via PMCR

• When TP/TO provided limits are less restrictive and create planning concerns (per the above values) the TP/TO may be asked to provide more restrictive limits to address such concerns

9

Development of corrective action plans

• Tap setting changes

• Corrections to conflicting voltage set points

• Transmission network reconfiguration, addition or upgrade

• Addition of reactive support (inductive or reactive)

• Develop Constraint Management Plans (if permissible)

10

Updates to analysis based on TPL-001-4

• Additional cases add to the 2015 RTP reliability analysis– Off-peak case

– Additional sensitivity cases for the peak and off-peak basecases

• Additional performance criteria to be included– Post-contingency deviation limit added

(implementations details being discussed at the PLWG)

11

ERCOT System Planning Voltage Stability Assessment

• Purpose: Identify the most severe contingencies with respect to the voltage stability margin

• Base Case: Peak load conditions are expected to present most critical scenarios for evaluating voltage stability margin.

• Voltage Stability Margin per the current ERCOT Planning Guide Section 4

– A 5% increase in Load above expected peak for NERC Category A or B operating conditions; and

– A 2.5% increase in Load above expected peak for NERC Category C operating conditions

12

Voltage Stability Assessment

• Start with the latest SSWG DSB and DSA cases

• Identify load centers with a potential for voltage stability concerns

• Perform PV analysis by increasing transfers into the load center until a condition of instability is achieved

• Work with TPs to determine investigate a solution to relieve the instability

13

Questions?

VOLTAGE STABILITY

JuanS.SantosPhDPETransmissionPlanningManagerRegulatoryAffairs&Compliance

1

Agenda DefinitionsTimeFramesForVoltageInstabilityMechanismsToolsforVoltageStabilityAnalysis ExampleSummary

2

Reactive Power (VAR) VAR‐ volt‐amperereactive(var)isreactivepowerisexpressedinanACelectricpowersystem‐ consideredaseithertheimaginarypartofapparentpower VoltageisdependentonVARs

RealpowerPisusedtosupplytheenergyrequiredtoperformactualwork(suchasrunningamotor),thereactivepowerregulatesthevoltageinthesystem.

Ifthereactivepoweristoolow,inductiveloadssuchasmotorswillbeunabletomaintain voltagesnecessaryforthegenerationofelectromagneticfields– asvoltagedipsmotorsrequiremoreVARs

Reactivepowertransmissiondependsmainlyonvoltagemagnitudeandflowsfromthehighestvoltagetothelowestvoltage.

Reactivepowersimplycannotbetransmittedlongdistances

3

Power Triangle

RealPowerP=MW

PowerFactor

Ø

TAN Ø = Q/P

4

Voltage collapse Voltagecollapseistheprocessbywhichthevoltagefallstoalow,unacceptablevalueasaresultofanavalancheofeventsaccompanyingvoltageinstability.Onceassociatedwithweaksystemsandlonglines,voltageproblemsarenowalsoasourceofconcerninhighlydevelopednetworksasaresultofheavierloading.Localissuethatcanhavewidespreadeffects.

5

Kundar,Prabha.PowerSystemStabilityandControl,McGraw‐Hill1994

6

Taylor,Carson.PowerSystemVoltageStability,McGraw‐Hill.1994

LoadflowstudiesStabilityStudies

7

Tools for voltage stability analysis1.P‐Vcurvemethod.2.V‐Qcurvemethodandreactivepowerreserve.3.MethodsbasedonsingularityofpowerflowJacobian matrixatthepointofvoltagecollapse.4.Noseofcurvedefinessystemlimits.5.criticalpointchangeswithtransmissionsystemtopology

8

SUMMER2020On‐Peak(14DSB)

SteamUnitOff‐line

ProblemStatement/Definition

9


1)SteamUnitOff‐line

2)SouthTieTrips

N‐1withtapssettingandswitchedshuntslocked

EnginePlantGeneratorsOver‐excited


10


1)SteamUnitOff‐line

2)SouthTietrips

3)FollowingtietripEnginePlanttripsforloadrejection

Startofvoltagecollapse


11

Summary Voltagestabilitycoversawiderangeofphenomena.

Voltagecollapseisuncontrollablelossofsystemvoltage.

Example:Phenomenastartsslow– endsupfast◦ loadbuildsup,voltagedips,(hours)◦ Linetrips(orsomeotherevent)– causinglargeVARdemand◦ Transformertapchanges,causingvoltagetodipmore(minutes)◦ Localgenerationbecomesoverexcitedandtrips.(minutes)◦ Importlinesneedtotransfermorepowerandbecomeoverloadedcausingvoltagetodipevenmore.(seconds)

◦ Withlowervoltageinductionload,suchasairconditioningloadsrequireadditionalvoltagesupport(milliseconds)….Deathspiral

Asvoltagedropsmotorsrequiremorevars.…. Undervoltage loadshed(Localareablackout)

12

Voltage ProfilesBill BlevinsManager Operations Planning

Voltage WorkshopApril 8, 2015

2

– What is the voltage profile?– Why provide Voltage Profiles?– Background protocols– Voltage Limit– Voltage Profile process– Future Outlook– Noted issues

Voltage Profiles - Summary

3

What is the Voltage Profile?

Voltage Profile The normally desired predetermined distribution of desired nominal voltage set points across the ERCOT System.

4

• Coordination! – As a Interconnection/region we need to make

sure voltages are coordinated.– We need to set profiles which will avoid

exceeding limits and keep the system coordinated. (keep the lights on, good utility practice, etc)

– Some generators may need to modify taps in order to meet the profile so we need to provide this information.

• This is rare but was more common practice in the multi control area period prior to Zonal start-up and coordinated voltage profiles.

• This can be identified through seasonal voltage profile study.

Why do we study and provide Voltage Profiles

5

NP 3.15(1): Voltage Support

ERCOT in coordination with the TSPs shall establish, and update as necessary, the ERCOT

System Voltage Profiles for all Electrical Buses used for Voltage Support in the ERCOT System and shall

post all Voltage Profiles on the MIS Secure Area. ERCOT may temporarily modify its requirement

based on Current System Conditions.

6

An over-excited (lagging or producing) power factor capability of 0.95 or less determined at the generating unit's maximum net power to be supplied to the ERCOT Transmission Grid and at the transmission system Voltage Profile established by ERCOT, both measured at the POI ;An under-excited (leading or absorbing) power factor capability of 0.95 or less, determined at the generating unit's maximum net power to be supplied to the ERCOT Transmission Grid and at the transmission system Voltage Profile established by ERCOT, both measured at the POI; Reactive Power capability shall be available at all MW output levels and may be met through a combination of the Generation Resource’s Unit Reactive Limit (URL), which is the generating unit’s dynamic leading and lagging operating capability, and/or dynamic VArcapable devices. This Reactive Power profile is depicted graphically as a rectangle. For Intermittent Renewable Resources (IRRs), the Reactive Power requirements shall be available at all MW output levels at or above 10% of the IRR’s nameplate capacity.

3.15 Voltage Support Reactive Power Requirement for Generation Resource

7

Season or Seasonal Winter months are December, January, and February; Spring months are March, April, and May; Summer months are June, July, and August; Fall months are September, October, and November.

What are the periods we issue the Voltage Profiles for?

8

VOLTAGE LIMIT

• Voltage Profile studies have a criteria that transmission voltage should not exceed 105% nor fall below 95% of the nominal system voltage. (Exceptions can be made for certain 69 kV equipment that is designed to operate at 66 kV or 64 kV, as well as for nuclear power plant switchyard busses.)

• Transmission voltage post contingency should neither fall below 90% nor exceed 110% of the per-unit voltage.

• ERCOT will utilize any voltage limits that are more restrictive than this criteria when determining the ERCOT System Voltage Profile set points.

9

Voltage Profile Process – Creating the Profile

1 2

3

10

Voltage Profile Process – Voltage Profile Group final review

VPG provides resolutions and exemptions if

necessary

Restudy?

No

ERCOT updates SSWG case

based on TSP revisions

Yes

ERCOT runs CA and

communicates results to TSPs

Violation?

No

Resolvable?Yes

TSP develops SPS or CMP for unresolvable

violations

No

Yes

End

ERCOT creates final voltage

profile report for Generator

POIs

11

New features

• Provide the Voltage Profile at high side of GSU (VAR-001-4)

• Include Scheduled Voltage updating in the Base Case

• Voltage limits provided by TSPs utilized if more restrictive.

12

Voltage Profile example

• Generator is expected to operate during that season at the voltage profile +/- 2% at the POI unless instructed otherwise by:• ERCOT or• ERCOT TO

13

Voltage Profile example

• Note many instructions may still be within the +/- 2%.• ERCOT should be notified if instructed to operate outside of 2% of

the voltage profile by the TOP. • Generator is expected to still operate within any equipment voltage

limits (e.g. set point is 1.035 pu and limit is 1.05 pu then range becomes +1.5% and -2% see example).

14

Voltage Profile Exemptions

• ERCOT is the only entity that can exempt generators from‒ following the Voltage Profile.‒ from having its automatic voltage

regulator (AVR) in service or from being in voltage control mode.

15

Future outlook

ALDR STUDY:

ERCOT Nodal Protocol, Section 3.15(6) requires ERCOT to annually review the Distribution Service Provider (DSP) power factors using the actual summer load and power factor information included in the Load data request to assess whether DSPs comply with the 0.97 Lagging PF requirements.

16

• Issues with getting all TSP companies involved

– No formal working group just list serve

– Generator Participation is after the fact

• Issues with how the profiles were originally set seems better.

– ERCOT proposed profiles originally

• TOs accepted and then ERCOT accepted

– Changed to:

• TO proposed then ERCOT studies and Accepts

• Some companies have differing opinions on how the profile is to beused in day to day practice.

• Difficult for ERCOT to monitor voltage profile performance if there isno way to track when different set points provided by the ERCOT TO.

Challenges

17

• Potential lag in generator reactive limitations being included in the studycases when considering the time frame from SSWG case creation tovoltage profile process.

• Voltage limits may differ between operations and planning

• Voltage schedules may differ between operations and planning

– ERCOT utilizes real time operational data to create voltageschedules to be utilized in the study cases in the OutageCoordination to Real Time timeframe.

– Planning voltage schedules may be utilized that are generic anddifferent.

• Seasonal voltage profile may have limited usefulness in areas wherevoltage variations are greater and require more frequent set pointchanges.

• Voltage Profile definition is at Point of Interconnection (POI) while thePOI is not always at the high side of the GSU.

Challenges (continued)

18

Questions?

3

ERCOT Issued Voltage Profile – Twice a Year

4

Tools utilized by AEP Transmission Operations

HABBE Connect – Analogs Download

SCADA State Estimator VSAT EterraVision

5

Visual Indication of Actual vs Issued Profile Voltages

Using the communication application HABDDE (Alstom product), AEP Real Time Operations brings SCADA Analogs for each plant within its footprint into an excel based spreadsheet where a comparison of issued profile vs actual voltage is monitored.

6

Visual Indication of Actual vs Issued Profile Voltages (continued)

7

Visual Indication of Actual vs Issued Profile Voltages (continued)

Using cell conditional formatting –voltage(s) can be highlighted for high/low range

8

SCADA Displays – designed to give a quick and concise overview of reactive devices in the footprint

9

SCADA Displays – designed to give a quick and concise overview of generator voltages in the footprint (continued)

10

E-Terravision Viewer Voltage Contour Maps

Using E-Terravision Viewer (Areva). Real Time Operators have the ability to view high/low voltage conditions through out the AEP footprint. Color contour mapping allows for a visual indication of voltage conditions both in real time or under contingency.

11

E-Terravision Viewer Voltage Contour Maps (continued)

Color contouring indicates voltages in a low to high range

12


P.U. voltages summarized by specified areas

13


P.U. windows can be created for specific areas – allows simple sorting by node (station), P.U, KV, etc.

14

VSAT Tool

Provides a system wide voltage analysis thereby leading an operator to address specific voltage as individual plants or buses.

15

Numerous tools can be utilized by real time operators to ensure proper voltage profiles are being followed as per ERCOT Operating Guides and Protocols.

Tools assist with situational awareness and facilitate real time operators in making proper decisions.

Summary

Outage CoordinationAlex Lee

ERCOT Voltage Workshop4/8/2015

ERCOT Voltage Workshop2/23/2015 2

Overview

• Responsibility

• Describe Process Timelines

• Outage Evaluation

• Voltage Reliability Criteria

• Voltage Issues and Resolutions

• Challenges


• ERCOT Protocol Section 3.1 Outage Coordination

Responsibility

Submit Outage

Approve Reject

Evaluate

Reliable?


Process Timelines

Transmission OutagesTransmission Outages

PLANSTART

91+91+ 46~9046~90 9~459~45 4~84~8 33Process

75 30 43 2Deadline

*all number in day

Resource OutagesResource Outages

33

PLANSTART

46+46+ 9~459~45 4~84~8Process

3 2Deadline Automatically AcceptedAutomatically Accepted5 business day

after submission5 business day

after submission

*all number in day


Outage Evaluation

OFFLINE EMS

Network Operations Model

Load Forecast

Resource Plan

Dynamic Rating

Voltage Profile

Outages

Power Flow

Contingency Analysis

Interface Study

Time-Based Model Analysis


• Power-flow: Normal High/Low

• Post-Contingency: Emergency High/Low

Voltage Reliability Limit

Default by kV Group by Company and kV level


Issues• Conflicting Outages

• Long radial system

• Transformer back-feeding higher kV system.

Resolutions• Adjust transformer taps

• Switch in/out reactive devices

• Reconfigure transmission system

• Bring on generation

• Mitigation Plan

• Reject the outage

Coordination


Typical Issues

~

~ ~

~

~ Rest of ERCOT

Outage 1

Outage 2Contingency

SmallSystem

69kV138kVA

B

C

D


• Distribution reactive devices

• Load Rollover

• Software – automatic control of reactive devices

Challenges


Questions?

10

LCRA Outage CoordinationERCOT Voltage WorkshopApril 8th , 2015

Daniel Marr, PEOperations Engineer

Process IntroductionOutage Coordination Procedural Overview

LCRA Transmission Services Corporation ▪ Owns / Operates:

▫ 5,100+ Miles of Transmission Line▫ 102 Power Transformers▫ 41 Auto Transformers▫ 829 Transmission Class Circuit Breakers▫ 3,300 + Protective Relays

▪ Time and Condition based maintenance creates a heavy scheduling and outage coordination burden.

▪ In 2014 alone, Coordination Personnel and Operations Engineering saw:

▫ An average of 220 Maintenance & Diagnostic Outages per Month▫ 358 Construction Related Outages

Process Flow-ChartOutage Coordination Procedural Overview

LCRA Planners

Short TermMaintenanceDiagnostics

Long TermNew Construction

‘Customers’

MaintenanceNew Construction

Database Tool

Outage Coordination Functions

Engineering Review

Contingency AnalysisVoltage / Overload

Switching Schedule

LCRA Operators

ERCOT

Outage Scheduler

Voltage Issues are Determined & Mitigated Here

Long Term Outage Process DetailsOutage Coordination Procedural Overview

Long Term Outage Review▪ 1 Construction Planner enters all capital project related outages.

Long Term Outage Process DetailsOutage Coordination Procedural Overview

Long Term Outage Review▪ An Operations Engineer conducts load flow and voltage/overload contingency analysis, approving and rejecting outages as necessary.

▫ Long-Term study cases are built utilizing the ERCOT Outage Scheduler.

▫ Study Cases are initially worst case and include all approved outages for requested window.

▪ The SOCC Outage Coordinator then submits the approved outages to ERCOT.

Short Term Outage Process DetailsOutage Coordination Procedural Overview

Short Term Outage Review▪ 3 Maintenance Planners enter all O&M outages into the Outage Coordination Database

Short Term Outage Process DetailsOutage Coordination Procedural Overview

Short Term Outage Review▪ The SOCC Outage Coordinator (NERC Certified Operator) then reviews the submittals for feasibility, communicating any issues.

▪ An Operations Engineer conducts load flow and voltage/overload contingency analysis, approving and rejecting outages as necessary.

▫ Short-Term Outage Cases are built using the ERCOT Outage Scheduler

▫ Each day of the week is studied separately

▪ The SOCC Outage Coordinator then submits the approved outages to ERCOT and generates the weekly Operator Switching Schedule.

OverviewOutage Coordination Engineering Review

Voltage Mitigation is Significant Part of Outage Approval Process▪ Operations Engineers utilize our GE EMS to conduct Load Flow and Contingency Analysis on every requested outage.▪ Voltage Issues are among the chief reliability reasons we reject or re-schedule outages.▪ LCRA consistently works alongside ERCOT Outage Coordination to mitigate potential voltage issues.

▫ A large percentage of the voltage issues discussed are remedied through switching or model verification. ▫ Outages with non-resolvable voltage issues are cancelled and rescheduled.

Common Voltage IssuesOutage Coordination Engineering Review

Back-feed of Load Through Auto▪ A common scenario involving a 138kV/69kV Auto with 138kV load at that station or a station away.▪ If T-218 were out, the loss of T-219 would lead to low voltage as 69kV System would attempt to feed load.▪ Mitigate through pre-contingent switching by opening 69kV CB 1550.

Common Voltage IssuesOutage Coordination Engineering Review

Large Voltage Swings Caused by Radial Capacitor Banks▪ Radially fed cap banks can cause significant swings, which if they approach more than 6% can cause distribution load to trip.▪ Loss of T-326 could lead to large voltage swing if CP1 is in service.▪ Mitigate by switching the bank out prior to the scheduled outage and alerting operators of the issue.

Operational Voltage IssuesOutage Coordination Operations & Planning

Real Time Voltage Issues▪ High voltage at transmission busses due to wind farm interconnects:

▫ 35kV bundled conductor used for collector lines act as capacitors when wind farm is offline.▫ Long 345kV lines, when switched out, can experience significant voltage discrepancies at the terminal ends.▫ Low-Wind output near wind farms can lead to low MW and high MVAR output.

▪ At times the only remediation is to open the affected circuit to reduce voltage – done in coordination with ERCOT.▪ Utilize a gradient voltage map that increases operator situational awareness.

ConclusionOutage Coordination Voltage Issues

Questions?

System Operations: Current and Next Day StudiesVoltage Control WorkshopApril 8, 2015

Jimmy Hartmann, Manager, System OperationsChad Thompson, Manager, Operations Support

Outline

• Background

• Next Day Studies

• Current Day Studies

• Real-Time Assessments

• Real-Time Coordination

• Other Tools

• Challenges

2

Background

• Tools of the Trade– Network Security Analysis

• State Estimator (SE) – executes every 5 minutes

• Real-Time Contingency Analysis (RTCA) –executes immediately following the SE

• Voltage Security Assessment (VSAT) – execute every 10 minutes

– SCADA Alarms• Triggered based on telemetry received from TOs

or QSEs

3

Background

• Tools of the Trade– Reliability Unit Commitment (RUC)

• Executes every hour• Considers voltage-related Generic Transmission

Constraints

– Off-Line Studies (STNET)• Available to operators and support staff to create

special ad-hoc assessments

• All applications consider Special Protection System (SPS) and Remedial Action Plan (RAP) actions

4

Background• Voltage Limits

– Provided by TSPs in the Network Operations Model

– Some TSPs utilize the default voltage limits identified in the ERCOT SOL methodology

Background• Voltage Schedules in the Network

Operations Model– In the past: ERCOT has used generic

schedules• Created questionable results in study cases

– Currently: ERCOT is utilizing voltage schedules based on real-time analysis and communications with TOs

• Results are much more improved

• ERCOT updates these schedules as necessary and quarterly at a minimum

Next Day Studies

• Next Day Steady State Study– Powerflow and contingency analysis

• thermal and voltage ratings exceedances are evaluated pre- and post-contingency

– Utilizes Current Operating Plan (COP) after Day Ahead Market (DAM) completes, latest Transmission outage information, and Load Forecast

– Peak Hour for the next Operating Day– Provides awareness to potential problems

that may arise in advance of large transmission outages

7

Next Day Studies

• Additional Ad-Hoc Peak Studies– Performed by Transmission & Security Desk

Operator, RUC Desk Operator, and Shift Engineer

– System conditions are changing continuously, ERCOT ISO runs multiple future looking studies for the next day’s peak hour and each hour to screen for any limit exceedances

8

Next Day Studies

• Daily Reliability Unit Commitment (DRUC)– Performed by RUC Desk Operator

– Utilizes COP, ran after DAM completes with latest Transmission outages and Load Forecast.

– Studies all 24 hours of the next day.

– Any voltage related GTLs are assessed to determine if a generating unit should be committed to allow for operation within the GTL.

9

Current Day Studies

• Hourly Reliability Unit Commitment (HRUC)– Utilizes latest COP, Transmission outages and Load

Forecast– Before DRUC - studies every remaining hour in the

current day – After DRUC - studies start at 1800 and all 24 hours

of the next day until midnight.– Any voltage related GTLs are assessed to

determine if a generating unit should be committed to allow for operation within the GTL.

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Current Day Studies• Current Day Future studies

– Steady State 4 hour-ahead study from HRUC• At 01:00, execute a study for 05:00 and review study

results to determine if additional actions are needed to meet potential voltage issues

• May create additional constraint management plans if necessary.

• May require TO validation and plan to address issues (e.g. Distribution side reactive support)

• If generation is needed to address a voltage issue, the Transmission & Security Desk Operator or Shift Engineer perform additional assessments to validate recommendations

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Current Day Studies

• Operations Support Activities– Chase down modeling and telemetry issues

– Real-Time outage evaluation

– Provide assistance and feedback to the Shift Engineer

– Discuss issues with TOs as requested by Shift Engineer or System Operators

– Facilitate development of Constraint Management Plans

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Real Time Assessments

– Shift Engineer• Monitor the SE and RTCA process and results

– Evaluate results for accuracy and validity

• Discuss voltage issues with TOs– Develop Constraint Management Plans

– Recommend creation of model change requests to update voltage limits in the network model for inaccurate voltage issues

• Perform off-line studies and provide feedback to the Transmission & Security Desk Operator

13

Real Time Assessments

• Real Time Contingency Analysis (RTCA) – Transmission & Security Desk Operator

• Monitor RTCA results for pre contingency and post-contingent voltage limit exceedances

• Work with Shift Engineer and TO / QSE to resolve issues

• Identify any available capacitors, reactors, or transformer taps

• Identify any nearby generators available to change their voltage set point when TOs need assistance

• Perform off-line studies and issue directives as necessary

14

Real-Time Coordination

• ERCOT coordinates with ERCOT TOs to address voltage limit exceedances to provided additional reactive support– Some exceedances are addressed by TO before

ERCOT ever calls

• TOs coordinate directly with Resource Entities for voltage adjustments– ERCOT can coordinate with the QSE to instruct

Resource Entities for voltage adjustments

• TOs and Resource Entities have direct control over their reactive support equipment

15

Other Tools

• System Operations Test Environment (SOTE) can be utilized by TOs to conduct ad-hoc studies utilizing ERCOT’s model and provided information.

• Voltage Support Service (VSS) tool can suggest solutions for CREZ for identified voltage limit exceedances.

• Telemetry is available via ICCP from ERCOT to help provide any information to assist in any TO real time studies.

16

Challenges• Sizing of reactive devices

• Inaccurate telemetry

• Modeling issues – new/old equipment

• Unplanned load variations– PUN load changes

– Significant load additions

17

Challenges• Wind generation variability

• 69 kV System– Limited telemetry; rely on State Estimation

– Solution to voltage limit exceedance resides on Distribution system – only TO has visibility on TO system

– Voltage on remote end of radial lines

18

Questions?

19

Real Time Voltage Control Basics for Generators

April 8, 2015

Real time Voltage Control for Generators (RE)

Overview

Real time Voltage Control for Generators (RE)Specific Responsibilities

ERCOT or the Transmission Operator (TO) may direct the QSE or plant personnel to adjust voltage on the unit.

Such output level directives are typically made directly to the plant control room personnel by the TO (except nuclear)

For nuclear plants, the TO relays such directives to the QSE who then relays the directive to the plant personnel.

The plant has 5 minutes to comply with the voltage change request.

If such directive cannot be met, the plant personnel will notify the TO of the reason for not meeting the directive and the anticipated time to meet the directive. The plant personnel will notify the QSE who will notify ERCOT.

Reasons for Not Meeting a TO Voltage Change Request

“Typical Generator Capability Curve and Operating Limits for a cylindrical rotor generator” from IEEE PES-PSRC Paper

“COORDINATION OF GENERATOR PROTECTION WITH GENERATOR EXCITATION CONTROL AND GENERATOR CAPABILITY”

Real time Voltage Control for Generators (RE) Resource owned switchable static or dynamic VAR devices

are controlled automatically, through SCADA or manually at the direction of the TO.

Plant personnel monitor the output voltage and reactive output of the generator. They also monitor the switchyard voltage with respect to the directives received from the TO. They do not currently monitor the switchyard voltage with respect to the ERCOT published voltage profile.

Excitation System BasicsThe excitation system supplies DC current to the voltage regulator which adjust the magnetizing current to the field windings of a synchronous generator thereby inducing AC voltage and current in the generator.

A PSS detects any changes in generator output power, controls the excitation value, and reduces any rapid power fluctuation.

Voltage Control Workshop

Stan MorrisManager, System Operations

1

Next Day

Outage Scheduling• Voltage control equipment• Switching plans• Field switchmen• Impact of outage on voltage and flows• Creating radial feeds with source re‐allocation

2

Next Day

• Outage Scheduling Cont.– Is this an interconnected tie line?

• Determine if outage impacts the interconnected TSP.• Contact neighboring LCC and verify impacts/concerns.

3

Next Day / Current Day

System ConfigurationValidate normal/abnormal configurationAvailability of reactive devicesAuto transformers and regulators in service.

4


• Mitigation Plans– Outage Coordination Temporary Operating Action Plan (OCTOAP‐M)

• All OCTOAP‐M’s are coordinated with and approved by ERCOT.• If applicable review for action needed to mitigate a contingency SOL

• If applicable and automated confirm the action is armed.– TNMP utilizes automated SCADA controlled actions to monitor line flows for certain known contingencies that create SOL conditions that need immediate mitigation. These actions are only armed in conjunction with line outages where a contingency can create an SOL.

5


• Condition Reports– Daily log of system conditions that impacts the system configuration or is in an abnormal state.

• Reports are distributed weekly to various departments to be addressed.

– Capacitor Reports included in the condition report.

6

Current Day

• Switching Activity– Review switching plans for changes and familiarization.

• Note any changes of system condition configuration reported at pass down.

– Contact appropriate parties impacted by switching.

• Interconnected TO’s• Industrial Customers

– Review and update condition report

7

Real Time Operations

• Voltage Control– Static Reactive Devices

• Transmission Capacitors– Utilize to allow dynamic resources operating room.

– Dynamic Reactive Devices• Connected Generation to Transmission System

– Utilize reactive capability on generator for voltage support when generator connecting bus is out of voltage profile.

8


• High Voltage Scenario– Lightly Loaded Lines

• Hurricanes and events that create an evacuation.– Analyze system to break into radial feeds.– Remove capacitors from service– Remove Auto‐Transformers from service

9


• Low Voltage Scenario– Peak Loading

• Place capacitors in service prior to peak to stay ahead of reactive absorption from loading.

– Loss of Resource• Generation

– Contact ERCOT Real Time Desk and advise of any voltage concern as a result of loss of generation.

• Tie Line Support– Contact neighboring TO

10


• Low Voltage Scenario cont.– Load Shed

• Mitigate System Operating Limits• Last Resort

11


• Monitoring– System Control and Data Acquisition (SCADA)

• Displays– Voltage Control Display– Station Display

• Alarming

– Weather• Radar

– Storm Activity

• Geomagnetic Disturbances

12

Questions?

Thank You

13

System Voltage Control in Real Time Operations

April 8, 2015

1

2

• Why do we need voltage control• Factors affecting transmission voltage• Elements of the transmission system used to maintain voltage• Consequences of not maintaining voltage• NERC Standard VAR‐001‐4 R1• Voltage Schedule• Suggestions for Protocol and Guide Changes

Agenda

Voltage Control is set at a High Standard When You Consider the Changing Conditions that Regularly Occur in Real Time

3

0.2 1.21.00.80.60.4

P.U. System Voltage

Hold Voltage Here0.95 – 1.05

• Monitored at Every Bus on the ERCOT System, 24 Hours a Day, 7 Days a Week, 365 Days a Year

• Timely because every Customer must have adequate voltage at all times to protect their equipment

• Timely because the ERCOT Markets all depend on continuously stable voltage

• Timely because risk of voltage collapse exists all the time on an electrical system and there is no acceptable number of preventable voltage collapses

4

Every Voltage Violation must be Addressed and in a Timely Fashion

• Weather & Temperatures 10º - 110º

• Time of Day

• Forced Outages occur near Planned Outages

• Generators come online/go offline (voltage support comes/goes)

• Storm Fronts move across Texas (voltages drop or climb)

• Wind Generation is erratic (effects voltage)

• 24/ 7/ 365

5

SystemConditions Change Hourly

For ALL System Conditions…

• A large part of load is air conditioning or heating load, and load increases when temperatures are very hot or cold

• As load (MW) increases, voltage decreases. . .

6

140 kV139 kV

Small load

140 kV135 kV

LARGE load

Fact: Station loads increase or decrease continually throughout the Day

Fact: Weather/Temperature Impacts System Voltages

Lightly Loaded Lines Produce VARs and Increase Voltages

Heavily Loaded Line Require VARs and Decrease Voltages

148 MVAR out357 kV

85 MVAR in 352 kV

VARs

VARs

Line MVAR LoadingsDynamicallyChange

Sw. Sta. #1Gen Bus #1

Gen Bus #1 Sw. Sta. #1Sw. Sta. #2

Sw. Sta. #2

Fact: As Line Loading Increases, Transmission Lines switch from Producing VARs to Requiring VARs and Voltages Decrease

Typical System Load Curve (MW) ‐ Winter

It Would Be Nice to Have a Typical Daily Load Curve to Help Anticipate What Voltages to Expect

9

7,000

9,000

11,000

13,000

15,000

17,000

19,000

1 Month ‐ November, 2013

Daily Load Curves for 30 Days (MW)

11/2411/23

Hourly LoadDynamicallyChanges

Load served by ONCOR

But, in the Real World, there is no “Typical” Daily Load Curve. Loads Vary Randomly as Texas Weather Changes…

10

60

65

70

75

80

85

90

95

100

105

110Au

g. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Sept. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Oct. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

D/FW Maximum Daily Temperatures

Actual Avg. Normal Temps95 Degreesin October ?!

“ BlueNorthers “

in Summertime

Summer – Fall 2014

TemperaturesDynamicallyChange

“Summer” Temperatures Regularly Vary from the Expected

11

0

10

20

30

40

50

60

Dec. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Jan. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

D/FW Minimum Daily Temperatures

Actual Avg. Normal Temps

EEA Event01/06/14

Early Winter in December(much colder than expected)

Winter 2013 ‐ 2014

TemperaturesDynamicallyChange

And Winter Temperatures Vary from the Expected

12

Load Load

Load Load

Load

Autotransformer

Autotransformer

Generator

Generator trips offline here and. . . . . . >

.

.

.

.

.< . . . . . . . . . . . .

Planned Outage

ForcedOutagehere

get Low

Voltagehere

Lines are Forced Out & Generators Trip Offline

Local voltage control problems are subject to the weaknesses in the local system

• Longer Lines have less concentration of VAR resources (a sparser mix

of capacitors, power plants, tielines)

• Voltage more impacted by Outages – both transmission and generation

• Larger daily load/voltage swings from less concentration industrial load

• Fewer Base Load Generators connected into local system

13

Voltage is Harder to Control for TO Facilities in Remote Locations

14

Real Time Operators must make small reactive equipment adjustments throughout the day and correct for whateverhappens.

15

Raises Voltage (Sources) Lowers Voltage (Sinks)Load Decreases ‐Losses Load Increases +Losses

Line Charging produces VARs Line Charging requires VARs

GEN Plants come online GEN Plants go offline

Automatic SVCs Automatic SVCs

Forced/ Planned Outages Forced/ Planned Outages

Raises Voltage (Sources) Lowers Voltage (Sinks)Capacitors Reactors

Voltage Control SVCs Voltage Control SVCs

Coordinate with TO Neighbors Coordinate with TO Neighbors

GEN Plants/ Raise Set Point GEN Plants/ Lower Set Point

Autotransformer Taps Autotransformer Taps

Shed Load (Last Resort) Open Lines (Last Resort)

Can't Control

Can Control

Although many conditions that impact voltage cannot be controlled, Real Time Operators can control reactive devices

16

or field current limiters as a result of increased load from motor stalling and LTC/TCUL actions.

Voltage Collapse Can Result from Failing to Maintain Base System Reactive Support

• Maintain system voltage within limits by using both dynamic and

static reactive resources

• Maintain adequate dynamic reactive reserves on all generating units

• Reactive reserve is the amount of dynamic resource MVAR

capability minus MVARs currently being used by that resource. In

other words, reactive reserve is the amount of MVARs left to respond

to a contingency, and prevent abnormal voltages or voltage collapse.

17

Goals of Voltage Control

18

Generator Voltage Targets remain where they are within the Voltage Profile to typically operate in the middle of their reactive capability ranges during normal conditions.

Add/remove static reactive devices while monitoring local voltages as system load changes• First, remove reactors as load increases• Add capacitors to stay in high end of voltage range so capacitors provide full reactive effect• Coordinate with Distribution to maximize distribution capacitors, coordinate with nearby Neighbors and adjust Autotransformer Taps

• Continue to monitor for areas where voltage is dipping and maintain dynamic reactive reserves• SCADA alarms warn if an area gets outside normal voltage range

An Example ‐ As Daily System Load is Increasing…

19

Begin to employ available dynamic resources to maintain system voltage

• Where necessary, request Generation Resource to raise their real‐time voltage target at the POI to which the plant is connected.• Real‐time voltage targets are determined by system conditions at that time.

The assigned voltage target will permit the generating unit to typically operate:• In the middle of its reactive capability range during normal conditions• At the high end of its reactive capability range during contingencies• “Under excited” to absorb reactive power under extreme light load conditions.

• Configuration of some remote areas or local outages or generator trips effect which resources are available and appropriate, and may effect how soon a resource is used.

After All Static Devices are Deployed in Local Area, Raise GEN Plants Voltage Where Required

20

Available

Raises Voltage (Sources) MVARs % Total

GEN Plants/ Raise Set Point 17,700 48%

Capacitors 14,100 38%

Coordinate with TO Neighbors 3,000 8%

Autotransformer Taps 1,000 3%

Brown Sw. Voltage Control SVC 840 2%

Shed Load (Last Resort) > 10,000

Available

Lowers Voltage (Sinks) MVARs % Total

GEN Plants/ Lower Set Point ‐14,300 59%

Reactors ‐6,200 26%

Coordinate with TO Neighbors ‐2,000 8%

Autotransformer Taps ‐1,000 4%

Brown Sw. Voltage Control SVC ‐780 3%

Open Lines (Last Resort) ‐3,000

None of the System Reactive Resources are Unnecessary or Not Used Under Certain Circumstances

Extreme Situations are:

• During Summer or Winter Peak seasons when the generation pattern happens to leave very few generators in a local area• When Forced Outages or Generation trips occur disadvantageously in a local area• In certain remotely located areas that periodically experience voltage limits violations

• A QSE should immediately notify ERCOT and the TO whenever a TSP or ERCOT directs a Generator to an alternate voltage schedule outside of 2% of the Voltage Profile, or if the Generation Resource cannot operate within 2% of the assigned Voltage Profile.

21

Occasionally, Conditions Arise Where TO will Request a Voltage Target Outside the Voltage Profile Range

Load

Load

Autotransformer

Forced BusOutage

Local voltage control problems are subject to the weaknesses in the local system

PlannedOutage

Tie to Neighboring TO

LTC

44 MW

AddCaps

Adjust Auto Taps

RequestNeighbor’sAssistance

Raise GeneratorVoltage Target

Example Scenario – Required to Raise Generator Voltage Target

22

VAR‐001‐4 TOP CFRR1. Each Transmission Operator shall specify a system voltage schedule (which is either a range or a target value with an associated tolerance band) as part of its plan to operate within System Operating Limits and Interconnection Reliability Operating Limits.

ERCOT ISO shall specify an ERCOT Interconnection VOLTAGE SCHEDULE (which is either a range or a target value with an associated tolerance band) for the point of interconnection for generators as part of ERCOT ISO's plan to operate within System Operating Limits and Interconnection Reliability Operating Limits.

Each Local Control Center shall specify a VOLTAGE SCHEDULE (which is either a range or a target value with an associated tolerance band) for its transmission facilities.

• Voltage Schedule – The TOP CFR defines the term “Voltage Schedule” in two ways:• For Generation Resources – Voltage Schedule means Voltage Profile• For Transmission Operators – Voltage Schedule means Transmission Voltage SOL

NERC Standard VAR‐001‐4 (Voltage Schedule)

23

24

What is Voltage Schedule?

Transmission Voltage SOL Voltage Profile

VAR‐001‐4 TOP CFRR1. Each Transmission Operator shall specify a system voltage schedule (which is either a range or a target value with an associated tolerance band) as part of its plan to operate within System Operating Limits and Interconnection Reliability Operating Limits.

ERCOT ISO shall specify an ERCOT Interconnection VOLTAGE SCHEDULE (which is either a range or a target value with an associated tolerance band) for the point of interconnection for generators as part of ERCOT ISO's plan to operate within System Operating Limits and Interconnection Reliability Operating Limits.

Each Local Control Center shall specify a VOLTAGE SCHEDULE (which is either a range or a target value with an associated tolerance band) for its transmission facilities.

• VAR‐001‐4 and TOP CFR define the Voltage Schedule as a range or a target value with a tolerance band

• Voltage Profile – Target Value with an Associated Tolerance Band• Transmission Voltage SOL – Defined as a Range

NERC Standard VAR‐001‐4 (Tolerance / Range)

25

Range (for Transmission Voltage SOL)

System Operating Limit Methodology for Planning and Operations Horizon

Effective Date: March 1, 2015

3.3.2 Operations Steady State System Voltage Limits

The following voltage ranges are considered to be the steady state system voltage limits in ERCOT for Operations purposes:

(1) 0.95 per unit to 1.05 per unit in the pre-contingency state

(2) 0.90 per unit to 1.10 per unit in the post-contingency state.

26

Target Value with Associated Tolerance Band(for Voltage Profile)

• ERCOT Nodal Operating Guide 2.7.4.1 (4)• “Except under Force Majeure conditions or ERCOT-permitted

operation of the Generation Resource, if a Generation Resource required to provide VSS fails to maintain transmission system voltage at the point of interconnection with the TSP within 2% of the voltage profile while operating at less than the maximum reactive capability of the Generation Resource, ERCOT may, at its discretion, report this to the Texas RE.”

• For voltage profile, how do we define Tolerance Band?

27

Proposed Changes for Incorporation Into the Nodal Protocols and Operating Guides

• Definitions• Voltage Profile (revision) ‐ The set of target values, which have a defined tolerance band, at the Points of Interconnection for Generation Resources across the ERCOT System. The Voltage Profile is studied for specific system conditions and determined biannually.

• System Voltage Schedule (new) ‐ The voltage limits at transmission stations across the ERCOT System.

• Voltage Target (new) ‐ The most recent voltage a generation resource has been requested to adjust to by it’s TO or ERCOT.

• Define a Tolerance Band for the Voltage Profile

28

Questions?

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