Steady-State Working Group:

Resource Modeling Discussion

Wes Woitt

September 27th, 2011

Areas of Concern

2

This year resource data is being pulled from RARF submittals into SSWG base cases

TSPs identified differences between historical models and RARF data in the following:

•Reactive capability

•GSU data

•Generator impedances and machine ratings (DWG to cover)

Reactive Capability (Generator Reactive Limits)

3

• Planning studies need to model realistic operational limits, not theoretical limits

• Qmax & Qmin values are very important for calculating system behavior

• Steady-state voltage studies• Voltage stability studies• Dynamic system studies

• Post-event analysis of major blackouts inevitably showed planning models with unrealistic reactive limits were contributors to false sense of security

Why do we care? Steady-State Voltage Stability Studies are affected

4

• Larger QMAX values for generation in the Houston Area result in an optimistic voltage stability limit.

• Results in a larger voltage stability margin and lower voltage collapse point than actually exists.

• Indicates over 900 MW more of import capability into the Houston area.

Why do we care? Transient Voltage Recovery studies are affected

5

CenterPoint Energy System dynamic bus voltages after a large disturbance

Historical QMAX and MBASE data Larger QMAX and MBASE data from July TP case

Results in 3824 MW of Under Voltage Load Shedding

Results in 0 MW of Under Voltage Load Shedding

Biennial Reactive Test Review

6

Protocol 8.1.1.2.1.4(2)

The Generation Resource Entity shall conduct reactive capacity qualification tests to verify the maximum leading and lagging reactive capability of all Generation Resources required to provide VSS. Reactive capability tests are performed on initial qualification and at a minimum of once every two years.

• Overview of lagging test (leading is similar)

• From test to base case

• From test to RARF

• Examples of errors in translation

Overview of Lagging Test Data Sheet

7

Test Data used in Planning

8

SSWG Procedure Manual

How is Q Max Calculated?

• Qmax is the maximum net lagging MVAr observed at the low side of the generator step up transformer when the unit is operating at its maximum net dependable MW capability.

• Qmax is calculated from the lagging CURL value by subtracting any auxiliary MVAr loads and any Load Host MVAr (Self Serve) load served from the low side of the generator step up transformer.

•  Numerical Example

- Lagging CURL = 85 MVAR

- Lagging test value = 80 MVAR (Gross)

- Auxiliary Load = 5 MVAR

-  Qmax is 85 – 5 = 80 MVAR

Use the CURL value here if the test value is equal to or greater

9

EXAMPLE: From Test Data to Planning Case

10

MAX CURL 348 MVAR

AUX LOAD 37 MW->21.5 MVAR @ 0.87 PF

IN Planning CaseQMAX: 348-21.5= 326.5 MVAR

Planning Tab of RARF

11

RARF Worksheet

12

7.0 Reactive Capability

The Reactive Capability section requires the submittal of the manufacturer’s capability curve as well as the 9-point curve values in the RARF. This information will be used to validate test data and should be the best design information available – including all reactive limitations. ERCOT will continue to require bi-annual testing, and this data will be used operationally.

Example: Using Test Data to fill out RARF

13

POINT 1 -> MW1 in RARFPOINT 6 -> MW4 in RARF

Point 1

Point 2

Point 3

Point 4

Point 5

Point 6

NET Gen Reactive= Gross- AUX Load

Questionable Test Data

Reactive Load???

14

SAMPLE DATA

15

NEW D CURVE DOES NOT SHOW 200 MVAR LIMIT SHOWN EARLIER

RARF data points do not match test or D curve

Example: Difference Between RARF &Test Data

16

D CURVE

Generator Step-Up Transformer Data from RARF

• There are some discrepancies in GSU Tap and Automatic Voltage Control settings

17

July ’11 Planning Case Using RARF data:

Data from latest DSB Case

Transformer TAB of RARF

Where To Get Additional Information ?

• RARF Asset Registration Guide

18

• RARF Glossary

• Contact Wholesale Client Services

Conclusion

• Modeling realistic reactive limits on generators is critical to transmission planning studies

• The realistic limits come from the reactive tests

• RARF data needs to reflect reactive tests

• Generator Step-Up Transformer data needs to be input as fixed with the actual tap setting

19

Questions

20