1. www.lcra.org Generator Test Data, Generator Capability Curve, and NPRR 366 Terms March 14, 2012 Mike Noth & Bracy Nesbit 1

2. www.lcra.org Common Interests Provide a stable and reliable system Comply with regulatory requirements (avoid non-compliance) Best value for customers 2

3. www.lcra.org Review of Generator Capability 3

4. www.lcra.org Area the Generator Can Safely Operate GENERATOR CAPABILITY 4

5. www.lcra.org Critical VSS Areas of Generator Operation Decreasing PF Increasing PF Decreasing PF 5

6. www.lcra.org NPRR 366 Problem The system needs to adhere to a voltage profile to remain stable No single generator can prop up or sink the system voltage 6

7. www.lcra.org 7 Simple Nomograph of voltage from Generator Terminals to BES

8. www.lcra.org The blue diamonds represent actual test points from leading and lagging reactive tests. Gen Gross are points measured at the Generator terminals. Red square represents 0.95 to 1.05 pu Voltage and +/- 0.95 power factor. Actual Generator Test Data – At Generator Terminals 8

9. www.lcra.org Dashed green lines roughly represent +/- 2% pu of Voltage profile value and bounded by red =/- 0.95 power factor lines. The blue diamonds represent actual test points from leading and lagging reactive tests. Net to BES are points measured at the POI. Red square represents 0.95 to 1.05 pu Voltage and +/- 0.95 power factor. Actual Generator Test Data – At POI 9

10. www.lcra.org Existing Nodal Protocol 3.15 (3) Generation Resources required to provide VSS must be capable of producing a defined quantity of Reactive Power to maintain a Voltage Profile established by ERCOT. Generation Resources shall comply with the following Reactive Power Requirements: an over-excited (lagging) power factor capability of 0.95 or less and an under-excited (leading) power factor capability of 0.95 or less, both determined at the generating unit's maximum net power to be supplied to the ERCOT Transmission Grid and at the transmission system Voltage Profile established by ERCOT, and both measured at the POI. The Reactive Power requirements shall be available at all MW output levels and may be met through a combination of the Generation Resource’s Unit Reactive Limit (URL), which is the generating unit’s dynamic leading and lagging operating capability, and/or dynamic VAr capable devices. This Reactive Power profile is depicted graphically as a rectangle. …continued… 10

11. www.lcra.org Existing Nodal Protocol 3.15 (3) Generation Resources required to provide VSS must be capable of producing a defined quantity of Reactive Power to maintain a Voltage Profile established by ERCOT. Generation Resources shall comply with the following Reactive Power Requirements: an over-excited (lagging) power factor capability of 0.95 or less and an under-excited (leading) power factor capability of 0.95 or less, both determined at the generating unit's maximum net power to be supplied to the ERCOT Transmission Grid and at the transmission system Voltage Profile established by ERCOT, and both measured at the POI. The Reactive Power requirements shall be available at all MW output levels and may be met through a combination of the Generation Resource’s Unit Reactive Limit (URL), which is the generating unit’s dynamic leading and lagging operating capability, and/or dynamic VAr capable devices. This Reactive Power profile is depicted graphically as a rectangle. …continued… 11

12. www.lcra.org Decreasing PF Increasing PF Decreasing PF PF=0.95 or Less Capacitive VAr devices have to be added Reactive VAr devices have to be added PF=0.95 or Less Present Protocol Requirement to meet the Voltage Profile There are no boundaries for the Generation Resource to supply reactive power in order to meet the Voltage Profile 12

13. www.lcra.org Back to the NPRR 366 Problem The system needs to adhere to a voltage profile to remain stable  The Generation Resource must operate to the operating point determined by the Transmission Operator No single generator can prop up or sink the system voltage  The Generation Resource will operate up to the generator capability 13

14. www.lcra.org Generating Resource Operating Modes Required to Meet the Voltage Profile – Generator Operating Point determined by Transmission Operator VAR-002-1.1b R2. Unless exempted by the Transmission Operator, each Generator Operator shall maintain the generator voltage or Reactive Power output (within applicable Facility Ratings1) as directed by the Transmission Operator. 14

15. www.lcra.org Nodal Protocol 3.15 Option A Revision ( 3) Generation Resources required to provide VSS must be capable of producing a defined quantity of Reactive Power to maintain a Voltage Profile established by ERCOT. Generation Resources shall comply with the following Reactive Power Capability Requirements: an over-excited (lagging) power factor capability of 0.95 or less and an under-excited (leading) power factor capability of 0.95 or less, both determined at the generating unit's maximum net power to be supplied to the ERCOT Transmission Grid and at the transmission system Voltage Profile established by ERCOT, and both measured at the POI. The Reactive Power Capability requirements shall be available at all MW output levels and may be met through a combination of up to the Generation Resource’s Unit Reactive Limit (URL)., which is the generating unit’s dynamic leading and lagging operating capability, and/or dynamic VAr capable devices. This Reactive Power profile is depicted graphically as a rectangle. A Generating Resource may meet this requirement using VAr capable devices…continued… 15