Managing West Texas Wind

SWEDE 2008 ConferenceMay 2, 2008

Presented by Paul HassinkAEPSC Texas Transmission Planning

The State of West Texas Wind

• Abundance of wind energy in Texas is so great that the State of Texas goal of 10,000 MW for 2025 will be achieved with Wind that is already committed

• Public Utility Commission (PUCT) proceeding on Competitive Renewable Energy Zones (CREZ) set out scenarios of 12 GW, 18.5 GW, and 25 GW of West Texas wind production

• On April 2, ERCOT’s report on CREZ Transmission Optimization (CTO) Study recommended a 345 kV plan to meet the PUCT request

• A minimum of five years is needed just to begin implementation of the extensive transmission plan resulting from the CREZ proceeding

PUCTCREZ

ERCOT Recommended

CREZ Plan for 18.5 GW(6.9 GW existing)

2.4GW

3.2GW

4.1GW

1.9GW

Synergies between Load and Wind

• Until the CREZ lines are ready to transport the wind, AEP Texas must continue to serve load, while addressing wind

• On the AEP Texas system, most wind farms are interconnected to the 138 kV and 69 kV systems

• These 138 kV and 69 kV systems, when built, were intended to support only 10’s of MW of load

• In order to connect wind farms faster and with less impact to land owners, existing lines provide paths for wind and an opportunity for system upgrades

• AEP Texas customers benefit from improved service from upgraded lines, and ERCOT customers benefit from more wind energy delivered sooner

Solutions Gleaned from Experience

• Path Reinforcement such as the rebuild or reconductor of lines

• Voltage Regulation at 69 kV near the load

• Isolation of load serving lines from generation serving lines

• Power flow Redirection via technologies such as phase shift transformers and series reactors

Path Reinforcement

• With over 1000 MW of Wind interconnected to the Abilene to San Angelo 345 kV line, additional transmission capacity is necessary to deliver wind production to ERCOT major load centers, particularly DFW

• Opening existing 345 kV and 138 kV lines to rebuild them would cause severe congestion

• Local 69 kV lines are in need of upgrades and can be rebuilt to provide new 138 kV paths to export wind energy

• Upgrading existing 69 kV lines improves reliability to customers and minimizes impact to land owners

Path Reinforcement

69 kV lines to be Rebuilt to Double Circuit serving Load at 69 kV and Wind at 138 kV

Voltage Regulation at 69 kV• Dynamic Reactive Compensation

– Minimizes the frequency of shunt capacitor switching

– Applies dynamic resource at load to mitigate the magnitude of voltage flicker

– Distributes dynamic requirement for stability enhancement

• Standard Configurations– 69 kV +/- 25 MVAR dynamic reactive with 138 kV

28.8 MVAR shunt capacitor bank– 69 kV +/- 50 MVAR dynamic reactive with 138 kV

57.6 MVAR shunt capacitor bank

Reactive Compensation Configuration

28.8/57.6 MVAR +/- 25/50 MVAR

138 kV 69 kV

McCamey Area Distributed Dynamic Reactive Resources

Desert Sky

King Mountain

TNC 69kVTNC 138kV

ForeignLCRA JDA

TNC SubWind FarmLCRA JDA

Reactive Device

Woodward

Indian Mesa

138 kV 57.6 MVar capacitor bank with +/- 50 MVAR dynamic reactive

compensation @ McCamey

138 kV 57.6 MVar capacitor bank with +/- 50 MVAR dynamic

reactive compensation @ Crane

Sherbino

138 kV 28.8 MVar capacitor bank with +/- 25 MVAR dynamic

reactive compensation @ Ozona

Isolation and Redirection

• With almost 7000 MW of West Texas wind production committed by the end of 2009, the overloads of the 138 kV and 69 kV lines west of Abilene and San Angelo will become routine

• By separating wind generation from the 138 kV and 69 kV lines that cross the interface between West Texas and ERCOT load centers, power can be forced to flow on the 345 kV system

• Additionally, Phase Shift Transformers can buck the power flow on 138 kV lines by increasing the power angle across the lines

Isolation and Redirection

Phase Shift Transformers block power flow from

weaker transmission systems

Split Busses in Substations Isolate Wind from Load and route wind to 345 kV system

345 kV Export Path

345 kVExportPath

Abilene

San AngeloBig Lake

Improved Reliability with Increased Wind Production

• Interconnecting wind generation well in excess of local load places the load serving transmission system at risk

• While the CREZ plan will alleviate the problem, it is at least five years away

• Separation of wind generation from load serving lines and the redirection of power flow to the bulk transmission system can buy time until CREZ lines are completed

• In the mean time, it makes sense to upgrade the capacity of the existing system, where there is a benefit to reliability

• Rebuilding 69 kV lines and adding dynamic reactive compensation improve service to customers, and increases transmission capacity for wind energy

Path Reinforcement

• Double Circuit 138/69 kV Lines (existing 69 kV lines with numerous load serving substations)

– Upgrades existing 69 kV lines with a trunk 138 kV circuit (second circuit) relieves the need to convert multiple small 69 kV substations and routes power from generation around the constraining 69 kV line

– Eliminates the need for a new right of way and potentially reduces overall footprint with less structures and single pole (as opposed to existing H-frame) designs

• ACCC Conductor (138 kV, composite core trapezoidal stranding)– High temperature ACCC conductor can double the rating of an existing 138 kV

line in less than 6 months at a fraction of the cost of rebuilding the line– Existing line must have significant remaining life

• Line Tension Monitors (345 kV and 138 kV, real time rating)– Since wind typically achieves its highest capacity during mild ambient conditions,

a significant amount of line capacity above the static rating is available when significant amounts of power are exported

– Day-ahead planning can estimate line capacity based on anticipated line MOT due to forecasted ambient temperature and cooling of wind correlated to wind production, enabling additional line capacity

Isolation of Load from Generation

• Sectionalizing 69 kV systems (normally open motor operated switches with RTU control and load break capability)

– Blocks power flow on parallel 69 kV lines at the expense of radial operation– Mitigated by additional parallel transformation, which provides backup to 69 kV

systems dependent on a single autotransformer• Bus Splitting (345 kV and 138 kV, double bus or in-line bus breakers)

– Substation designs or reconfigurations that provide the flexibility to isolate through path wind generation lines from load serving lines with normally open breakers

• Line Bypass (345 kV and 138 kV, line rerouting outside of substations)– Applications where flexibility is not needed, lines can be rerouted around

substations to provide an express path for generation and balance power flow• Attaching IPPs to Spare Circuits (345 kV and 138 kV, double circuit lines

with an empty position)– Overload of the line/path can be relieved by connecting IPPs to a new circuit on

an empty position of an existing or rebuilt line, and moving the point of connection to the grid to a substation with adequate interconnection to the bulk system

Power Flow Redirection

• Phase Shift Transformers (138/138 kV PST, 150/200 MVA, +/- 30 degrees, in-line LTC, with bypass breaker)

– Many of the underlying 138 kV lines cannot be rebuilt without extensive rebuilds that extend down stream into other 138 kV systems, so a PST can applied to block 138 kV power flow from wind generation, diverting the power to the 345 kV system

• Series Reactors (138 kV / 300 MVA and 69 kV / 100 MVA, 10-20 ohms, with bypass breaker)

– Similar to PST, but for applications with less sever overloads and that are not voltage constrained

• Series Capacitors (345 kV, 0.03 pu, 2000 MVA, segmented)– Redirects power from constrained 345 kV lines to 345 kV lines with reserve

capacity, thereby relieving constraints at 345 kV and improving stability