Utilizing High-set Load Shedding Schemes (UHSLSS)

to Replace Responsive Reserve Obligation

Juan S. Santos(512) 248-3139 • jsantos@ercot.com

Senior Consultant, System PlanningTechnical Operations

Study Scope Review

Topics From the Study Scope

• Objective of study

• Method Of Analysis

• Study Approach by tasks

• Report and Criteria for acceptance

• Estimated Cost and Timeline

Objective of Study

• The current ERCOT rule allows for 25% of the ERCOT 2300 MW Responsive Reserve

Obligation stability classification, or 575 MW, of interruptible load tripped at 59.6 Hz to be substituted for responsive reserve.

• The objective of this study is to investigate how much of this limit can be increased without significant negative impacts on the ERCOT system.

Method Of Analysis

• This study will compare the effects of replacing increasing amounts of responsive spinning reserve with hi-set interruptible loads set to trip by automatic relays with a time delay of not more than 20 cycles.

• Study will monitor, frequency, bus voltage, rotor angles, speed, megawatts, mega-vars, terminal voltage, and exciter field voltage.

• Study will also scan for any out of step conditions.

• A solved load-flow case will be saved and examined for abnormal network conditions at the end of the dynamic simulation period.

Task 1 – Assembly And Sanity Check Of Data

• Data of the base models will be provided by TSP’s •2002 spring and summer cases

• Data in PTI PSS/E format will be assembled by ERCOT staff – flat start • Data collection and sanity checking

PowerflowDynamic initialization

Any data questions or problems identified will be brought to the attention of DWG members and resolved with recommended modifications approved by DWG

• Data does not include boiler models (simulations limited to 15 sec)• Loads to used as is without scaling them to match the actual ERCOT loads

on any given day.

Task 2 – Development Of Scenarios And Criteria

Four scenarios will be assembled representing increasing levels of HSLSS High Set Load Shedding Schemes

• Base Case – 100% of spinning reserves as “real” generation.

• Case 2 – Use High-Set Load Shedding Schemes (HSLSS) to replace 50% of the Spinning Reserve.

• Case 3 – Use High-Set Load Shedding Schemes (HSLSS) to replace 75% of Spinning Reserve.

• Case 4 – Use High-Set Load Shedding Schemes (HSLSS) to replace 100% of the Spinning Reserve.

Task 3 – Add/Modify High Set Load Relays

• Placement of Replacement Reserve Service (RRS) will be set at several different levels:

1. Trip level to be set at 59.7 Hz for 20 cycles.2. Trip level to be set at 59.8 Hz for 20 cycles.3. Trip level to be set at 59.9 Hz for 20 cycles.

• Load RRS to be selected using a non-bias approach based on size and location.

Task 4 – Run Full Analysis for Each Scenarios

Case 1 - 25%

Case 2 -50%

Case 3 -75%

Case 4 -100%

Level a:

59.7A1 A2 A3 A4

Level b:

59.8B1 B2 B3 B4

Level c:

59.9C1 C2 C3 C4

Report and Criteria

• Working Group members will write report and recommendations

• If any scenario studied fails to meet all of the following criteria,it will be considered unacceptable.

1. No abnormal system conditions leading to cascading outages and system collapse.

2. No firm load will be shed. To ensure this the minimum allowable frequency in the study will be shed for that stage.

3. Maximum frequency deviation based on ANSI/IEEE Standard C37.106-1987, Guide for Abnormal Frequency Protection for Power Generating Plants.

Estimated Cost and Timeline

•This study will require each working group member’s time. Time = Money•Will require the formation of working group members who will have to commit a large amount of time.

•4 people 12 days or 384 man – hours •Work group will meet (min.) four times for three days •Report writing will require an additional 160 man-hours