Houston Area Dynamic Reactive Project

March 11, 2011

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Background

Houston area becomes high import area in 2002 NRG (formally Texas Genco) retires 3800 MW in early 2005 Dynamic reactive support lost Houston imports 25% or more of load requirement from resources

external to the CenterPoint Energy footprint

Local dynamic reactive supply has declined• More vulnerable to voltage collapse• Houston’s high concentration of residential air conditioning load makes the

situation worse• Load continues to grow

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With units on-line With units off(Voltage Collapse)

3-phase fault with delayed clearing

Effect of Retiring 3800MW of Local Generation

Steps Taken to Address Voltage Stability Concerns

Under voltage load shedding (UVLS) scheme at CenterPoint Energy completed in 2005

Participation in EPRI load modeling efforts 2004-2010 More than 1550 MVAR of capacitor banks added to the

transmission system since 2005 Houston Area Constraint Mitigation projects

STP – Hillje – WAP circuits Singleton and Zenith substations Fayetteville – Zenith circuits

Installed a total of 280 MVAR of dynamic reactive compensation in 2008 TSC’s at Bellaire and Crosby 140 MVAR each

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Recent and Future system developments

Received Notices of Suspension of Operations for approximately 900 MW of generation (~470 MVAR of total continuous reactive capability) within the past year

2014 maximum Houston import UPLAN dispatched case with recently approved transmission projects shows an additional 1800 MW of local Houston area generation offline.

ERCOT’s December 2010 Long-Term System Assessment Report highlights the need for additional supply of local dynamic reactive power and “will conduct further analysis of these potential reactive needs in cooperation with the transmission service provider for the Houston area”

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Houston Dynamic Reactive Study

Dynamic analysis is required to determine proper dynamic reactive compensation solution 2013 Summer Peak base case UPLAN Generation Dispatch provided by ERCOT

Dynamic analysis requirements Detailed generator models, complex load models including induction

motors, UVLS models, and Over-excitation limiter models Disturbance studied: 3-phase fault cleared by breaker failure

relaying taking two elements out of service• NERC Category D• No more than 1250 MW of UVLS should be lost - Reserve a portion of

UVLS as safety net due to modeling uncertainties and avoid over-frequency excursions

• Transmission system voltages must recover so that no generator terminal voltage remains below 90% of rated voltage for more than 10 seconds.

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Study methodology

Contingency Screening Time domain contingency screening to determine worst case event Contingency #58 proved to be the worst case event leading to Fault-

Induced Delayed Voltage Recovery violating both aspects of the performance criteria

Load modeling sensitivities Various types of load models were considered including large, small,

and air conditioning motor models Load model sensitivity analysis also includes a variation of the motor

model parameters Load Model #1 – represents large and small motors with

conventional induction motor models Provided more reasonable and realistic results Development research for Load Model #2 is still ongoing

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Houston Dynamic Reactive Study

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Load Model #1 - 2013 Base CaseResults in 5185 MW of UVLS Eight local generator terminal voltages do not recover to 90% voltage within 10 seconds

Voltage Recovery Solutions

Dynamic reactive device technologies considered STATCOM STATCOM with Overload Capability SVC TSC

Additional option to package each technology with an additional Mechanically Switched Fixed Capacitor

Dynamic models of distinct characteristics of each technology were included

Primarily concerned with capacitive compensation to satisfy performance requirements

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Location Considerations

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2008 Installations

New Proposed Installations

Dynamic Reactive Projects

ROTHWOOD

ZENITH

ADDICKS BELLAIRE

CROSBY

Required Dynamic Reactive Devices Ratings

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Type of Dynamic Reactive Device

Addicks & Rothwood Addicks & Zenith

MVAR capacitive output of each

device measured at High side voltage

Resulting MW Load Shed

MVAR capacitive output of each

device measured at High side voltage

Resulting MW Load Shed

STATCOM OC Short-term rating 371

1190347

855Continuous rating 139 130

STATCOM OC w/140 MVAR FC

Short-term rating 2781232

278754

Continuous rating 104 104

STATCOM 383 783 360 783

STATCOM w/140 MVAR FC 293 783 270 1185

SVC 518 1232 518 1148

SVC w/140 MVAR FC 428 1157 428 783

TSC 540 1061 540 783

System voltage recovery with SVC Example

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System voltage response with addition of 518 MVAR SVC

Results in 1148 MW of UVLS All local generator terminal voltages recover to 90% voltage within 10 seconds

Proposed Schedule

February 2011: Project submitted for RPG comments

March – May 2011: ERCOT Independent Review

June 2011: Bid package and specification released to vendors

February 2012: Award contract to vendor

2nd Quarter 2014: Complete Commissioning

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Summary

Houston area in need of dynamic reactive support due to generation retirements, increased imports, and load growth

CenterPoint studies showed a need for 350 – 550 MVAR of dynamic reactive compensation at two sites each in order to satisfy performance criteria

Final amount of reactive compensation will be dependent on technology type and vender bids.

Estimated cost is $125 million Estimated completion date in 2nd Quarter 2014

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