TRANSMISSION CONSTRAINTS

KENNETH A. DONOHOO, P.E.

Manager of System Planning, Technical

Operationskdonohoo@ercot.com

9/13/2001

TERMS

• VOLTAGE volts pressure• CURRENT amps flow• POWER watts volts x amps• FREQUENCY hertz cycles/sec• CONTINGENCY outage out of service

9/13/2001

ELECTRICITY CHARACTERISTICS

• Travels at the speed of light

• Cannot be easily stored • Cannot be fully “routed”• Line flows not easily

changed• Network must be

continuously connected to function correctly

• Supplied immediately upon demand by customer

9/13/2001

BUT IT’S NOT LIKE...

• The natural gas pipeline system

• The telephone system• The water system• The transportation

systemIT CAN’T BE EASILY ROUTED!

Power flow is based uponPhysical Laws not Contracts

9/13/2001

ORIGINAL PURPOSE OF TRANSMISSION

• Connect generators to each other and to the distribution system• Contingencies (outages) and

economic dispatch• Connect utilities to each other

• Security• Interchange

• Built to serve known customers (loads) within utilities’ own territory, with relatively weak inter-utility links.

9/13/2001

TRANSMISSION CONSTRAINTS

• Function of the Impedance And Voltage Of Network

• Thermal Limits• Heating of Conductor, Transformer or Facility• Dependent on weather• Longer Term - 10 to 40 minutes

• Voltage Limits/Stability• Reactive Problems• Very Short Time Frame• Voltage Collapse

• Unit Stability Limits• Angular & Generation Unit Stability• Very Short Time Frame

9/13/2001

DYNAMIC UNIT

STABILITY

9/13/2001

Greatly Simplified

AB

Transaction From A to BA is Exporting, B is ImportingPower Flows on Primary Paths as well as ALL the Parallel Paths

C D

Ckt 1

Ckt 2

Ckt 3

Ckt 4

Ckt 5

Ckt 6

Ckt 7

Ckt 9

Ckt 8

PRIMARY PATH

PARALLEL PATH

PARALLEL PATH

PARALLEL PATH

9/13/2001

Greatly Simplified

AB

C D

Ckt 1

Ckt 2

Ckt 3

Ckt 4

Ckt 5

Ckt 6

Ckt 7

Ckt 9

Ckt 8

PRIMARY PATH

PARALLEL PATH

PARALLEL PATH

PARALLEL PATH

AS THE POWER FLOW INCREASES, FLOWS ON PRIMARY PATHS AS WELL AS THE PARALLEL PATHS INCREASE.

THE TRANSFER LIMIT (CONSTRAINT) IS REACHED WHEN ANY ONE OF THE FOLLOWING CONDITIONS IS REACHED:

•FLOW ON CIRCUIT WOULD BE AT THE LIMIT FOR POST-CONTINGENCY LOADING•VOLTAGE ON A BUS WOULD BE AT MINIMUM POST-CONTINGENCY VALUE•SYSTEM REACHES A STATE OF VOLTAGE INSTABILITY LEADING TO COLLAPSE•SYSTEM IS NOT VOLTAGE STABLE IF A CONTINGENCY WERE TO OCCUR•SYSTEM IS NOT DYNAMICALLY STABLE IF A DISTURBANCE WERE TO OCCUR

9/13/2001

Power Flow From A to BA is Exporting, B is ImportingContingency on Circuit 2Increase Generation in ADecrease Generation in BUntil Limit Reached on Circuit 9Net Change in Generation is Transfer Limit

CALCULATION EXAMPLEGreatly Simplified

AB

C D

Ckt 1

Ckt 2

Ckt 3

Ckt 4

Ckt 5

Ckt 6

Ckt 7

Ckt 9

Ckt 8

PRIMARY PATH

PARALLEL PATH

PARALLEL PATH

PARALLEL PATH

CONTINGENCY (OUTAGE)

X

LIMITING EQUIPMENT

9/13/2001

CALCULATION EXAMPLEGreatly Simplified

AB

C D

Ckt 1

Ckt 2

Ckt 3

Ckt 4

Ckt 5

Ckt 6

Ckt 7

Ckt 9

Ckt 8

PRIMARY PATH

PARALLEL PATH

PARALLEL PATH

PARALLEL PATH

CONTINGENCY (OUTAGE)

X

LIMITING EQUIPMENT

Rating on Circuit 9May Also Limit TransfersFrom A to Cand A to D

Simultaneous Flows From Any AreaMay Contribute to Flow on Circuit 9

ACTUAL CALCULATIONS INCLUDE MANY MORE CIRCUITS & EQUIPMENT

9/13/2001

• TRANSMISSION CONSTRAINTS• Complicates System Security Management• Leads to Economic Inefficiencies• Creates Captive Markets• Reduces Liquidity of the Market• Creates “Must Run” Generation• Increased Utilization of Inefficient Units• Reduced Utilization of Efficient Units• Confers Market Power to Dominant

Supplier in a Constrained Area

CONSIDERATIONS

9/13/2001

• NEW TRANSMISSION• Maintains Reliable Service to Load• Allows New Generation to be Fully

Integrated into the Grid• Provides for Additional Competition• Promotes Lower Energy Prices• Supports a Liquid Competitive Market• Allows Greater Access to Renewable

Generation

CONSIDERATIONS

9/13/2001

MONTICELLO-FARMERSVILLE 345 kV

CIRCUIT

AUSTROP-LOST PINES-FPP 345 kV

CIRCUIT

LYTTON-HOLMAN-FPP

345 kV CIRCUIT

LIMESTONE-WATERMILL 345 kV

DCKT

MILITARY HIGHWAY STATCOM +/- 150

MVAR

NEW MAJOR TRANSMISSIONFOR 2001 SUMMER

9/13/2001

COLETO CREEK–PAWNEE 345 kV LINECCN DECEMBER 2000IN SERVICE MAY 2002

SAN MIGUEL–PAWNEE 345 kV LINE

CCN NOVEMBER 2000IN SERVICE MAY 2002

FARMERSVILLE-ANNA 345 kV

CCN JANUARY 2001IN SERVICE DEC

2002

MORGAN CREEK–SAN ANGELO–COMANCHE SWITCH 345 kV

LINECCN JUNE 2001

IN SERVICE DEC 2002

GRAHAM – JACKSBORO 345 kV LINECCN FILED BY JUNE 2001

IN SERVICE DEC 2002

RIO GRANDE VALLEY SERIES CAPACITOR COMPENSATIONIN SERVICE SEPTEMBER 2001

MAJOR TRANSMISSIONPROJECTS UNDERWAY

HOUSTON AREA

UPGRADES

PARIS-ANNA 345 kVIN SERVICE DEC 2005

VENUS LIGGETT 345 kV

IN SERVICE DEC 2004

9/13/2001

PEAK DEMAND

YearERCOT Coincident Hourly

Peak Demand MWAnnual Growth

1994 43,588 --

1995 46,668 7.07%

1996 47,683 2.17%

1997 50,150 5.17%

1998 53,689 7.06%

1999 54,849* 2.16%

2000 57,606 5.03%

Average Six Year Compound Growth 4.85%

*This value would have been greater if there had been no interruptible load curtailments at the time.

9/13/2001

FUTURE GENERATION

CAPACITY RESERVESOFFICIAL MARGINS

Based on System Planning Technical Operations forecast.Assumes all generation capacity is available during peak conditions.Only includes future generation plants that have an executed/completed interconnect agreement with an ERCOT TSP.Does not include DC Tie Capacity or generation plants that can switch between regions.Does not include wind generation capacity.

Includes Serving Interruptible Loads

SUMMER Percent Reserve Margin Year 2002 2003 2004 2005 2006 22.5% 21.7% 18.5% 14.9% 11.4%WINTER Percent Reserve Margin Year 2002/03 2003/04 2004/05 2005/06 2006/07 58.3% 64.9% 65.5% 61.5% 57.5%

9/13/2001

ERCOT TEAMWORK

&

ATTITUDE GOES A

LONG WAY

9/13/2001

QUESTIONSFOR MORE DETAILS AND ADDITIONAL SYSTEM DATA

VISIT THE SYSTEM PLANNING TECHNICAL OPERATIONSWEBSITE AT:

ftp://ftp.ercot.com/systemplanning/system_planning_department.htm