CREZ Optimization Studies

765kV Schemes for 24+ GW Total Wind

Cathey Carter, PERPG CREZ meeting 3/10/2008

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Evaluating a Transmission Improvement Plan

• Would it work? – % total wind curtailment from UPlan– Contingency analysis from PSS/E and MUST

• Could it be operated?– Voltage, transient, and angular stability analyses

• Could it be built?– Professional judgment of the TDSP engineers

• How much would it cost to build and operate in comparison to other plans?– Standard proxy prices were discussed and agreed to by

this group last fall.

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The Tools

• PSS/E – User sets up topology, loads, and generation

dispatch– Program calculates voltages and power flows– Program does not consider economics

• MUST– User sets up topology, loads, generation

dispatch, contingencies, and transfer subsets– Program calculates contingency overloads and

transfer limits between defined subsets– Program does not consider economics

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The Tools

• UPlan – User sets up topology, load patterns,

contingencies, and generation characteristics– Program models time series of real power flows

and generation dispatches– Program is does not consider voltages and

reactive power flows

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The Study: Distribution of Wind Generation and ERCOT Load

AreaBase Wind

Scenario 3 Wind

Scenario 4 Wind

Max Load

Panhandle A & B 60 8,740 6,720 0

McCamey 755 3,645 3,945 <200

Central &

Central West5,288 11,674 12,954 2,600

Houston 0 0 0 23,200

Dallas 0 0 0 23,200

Austin &

San Antonio0 0 0 11,400

Balance of System

800 800 800 19,200

Total 6,903 24,859 24,419 79,800

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Relative Distances from Wind Gen to ERCOT Load

DFW

(23,200 MW)

Houston

(23,200 MW)

San Antonio, Austin

(11,400 MW)

Panhandle

(8,740 MW, 6,720 MW)265 465 375

McCamey

(3,645 MW, 3,945 MW)320 400 265

Central & Central West

(11,674 MW, 12,954 MW)220 355 240

Please refer to pages 22-24 of Dr. Navin Bhatt’s presentation to the 9/28/2007RPG CREZ meeting for the St. Clair Loadability Curve. This shows the decreasingline loading limit with increasing length per line voltage. The limit is a function ofstability and voltage drop. Series compensation can reduce the voltage drop.

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The Study: Minimum Load and Minimum Dispatch

2012 ERCOT minimum load at 4/8 4AM30,782 MW (+ losses)

Minimum generation of 3 nukes 3,640 MW

Difference = 27,142 MW

Scenario 3 wind generation to study24,859 MW

Note: 24,859 / 27,142 = 91.6%

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The Study: 2012 Load Levels

ERCOT load% of time in 2012

Scenario 3 Wind as a percentage of

[Load – Min(3 Nukes)]

≤ 40,000 MW 25 68

≤ 44,077 MW 50 61

> 50,000 MW 26 54

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Methodology - Load

UPlan was used with Scenario 2 plans to choose several hours to study:• Maximum (Wind generation – west area load)

• 4/2, 4AM Wind = 12,700 – 15,500 MW• Load = 33,845 MW

• Maximum load• 8/2, 5PM Wind = 2,074 MW• Load = 78,630 MW

• Minimum load and wind• 4/6, 5AM Wind = 2,062 MW• Load = 31,163 MW

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Methodology – Load, Generation

• The 4/2 4AM load was advanced to the 2018 load for the same day and hour: 36,257 MW. • UPlan calculated the wind generation of the Scenario 2 “765kV Backbone” model at 4/2 4AM to be 12,700 MW, or about 70% of the 18,456 MW.

• An AC model for Scenario 4 based on the 765kV backbone at 36,257 MW load can be considered “comparable” to the Scenario 2 plan when it is N-1 secure at wind generation = 17,093 MW, (70% of Scenario 4: 24,419 MW).

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Methodology – Generation

• The rest of the generation in the AC models should be about 36,257 + Losses – 17,093. This is about 20 GW.

• UPlan calculated the April capacity factor of all the non-wind generators for “unconstrained” conditions. They were ranked by CF and the first 20 GW were selected.

• Pmin of all cogens was adjusted to 50% of Pmax, and Pmin of coal units was set to no higher than 50% of Pmax

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Comments

Please direct comments to Warren Lasher or Cathey Carter.

Warren: wlasher@ercot.com

512-248-6379

Cathey: ccarter@ercot.com

512-248-3978