Minutes of DWG Meeting

Minutes of DWG Meeting

Minutes of DWG Meeting

Austin, Texas

May 30-31, 2006



Vance Beauregard, Vice Chair,



Reza EbrahimianAustin

Sharmilla Gurrala CPS Energy 210-353-2176




Wes Woitt,

Tuesday May 30th, 10:00 am - 5:00 pm, MET Room 168

Wednesday May 31st, 9:00 am – 3:00 pm, MET Room 168

DWG Discussion10am-12pm

  1. Wind flat start issues – Discussed confidentiality issues for wind turbine models. All of the models in this year’s update can be provided to DWG members, but some of the wind turbine technologies for future windfarms, such as the newer Micon models, have confidentiality issues. ERCOT Legal has taken the position that a Non-Disclosure Agreement (NDA) signed by ERCOT represents ERCOT only, and does not guarantee that other parties will abide by ERCOT’s NDA. Each company that wants to run studies with wind turbine models would have to sign a NDA with each wind turbine manufacturer. It was pointed out that DWG dynamics data is already confidential, and that TSP’s must share information due to proximity of windfarms.
    An alternative is to revise the Procedural Manual language to make it clear that all wind turbine manufacturers, that want to connect to the ERCOT grid, are required to make their models available for all companies for use in system studies. The target is to get the revised language to ROS for confirmation at their August meeting, and then to incorporate it into the Procedural Manual update in September, and get ROS approval on the whole manual at their October meeting.
    There are two versions of the models for GE and Vestas machines in this year’s flat start: the ERCOT models and the latest PTI models. John used the latest PTI models for his runs, but DWG members may use the ERCOT models instead, if they prefer. There will be changes needed to bus numbers, and possibly some of the dialog.
  1. UFLS Assessment
    ROS gave a waiver to the DWG on having to run a new UFLS study this year. However, there is a NERC requirement to do UFLS assessment every five years. The group discussed whether an assessment can be done without actually re-running the study. Mark Henry seems to think that the assessment required by NERC does not necessarily require a new simulation to be performed.
    The main issue of the assessment is whether the UFLS relays help the system to recover from a generation loss. Some of the older electromechanical relays have been replaced with solid state relays. The group decided to review the last assessment and modify it based on recent experience, including relay change-outs, lessons-learned about governor response, and changes in generation patterns due to mothballing of units. Wes will review the previous assessment and prepare a draft assessment.
  1. List of PSS from Powertech study
    Wes will report to the PSS Tuning Task Force the list of critical units with Power System Stabilizers. Vance supplied the units in the AEP system from the PowerTech study, and Roy supplied the TXU system units based on the PowerTech study and more recent studies that include newer units.
  1. Bob Millard of ReliabilityFirst gave a presentation on the field test program for four NERC Generator Related Standards. The standards are:
    MOD-026 – Generator Excitation System Verification
    MOD-027 – Generator Frequency Response Verification
    PRC-019 – Generator Coordination Information
    PRC-024 – Generator Performance During Excursions
    The purpose of the field test is to determine the practicality and technical feasibility of the proposed Standards, and whether they are comprehensive enough and achieve the desired result.
    The DWG is charged with establishing and distributing procedures to address verification and reporting for 3 of the Standards. The Generator Owners are to follow the regional procedures for verification and reporting. For PRC-019, ERCOT will only determine exemption criteria. The presentation contained timelines and descriptions of deliverables for this project.
  1. Leonardo Lima and Paloma DeArizon of Siemens PTI gave a presentation on generator testing and model validation, including staged tests done while the unit is down, and a new method based on on-line monitoring, which does not require that the unit be removed from service (a major cost component).
  1. Ken Donohoo reviewed the responses to the Combined Cycle RFP. He will send out the responses to DWG members for their review and comment. Issues include whether to get Combined Cycle models for PSS/e only, or to include PowerTech labs software; whether testing of plants will be included and if so how many plants; and of course, project cost.
  1. Voltage Collapse Criteria
    The group discussed Voltage Collapse Criteria at length. Wes presented CenterPoint’s Proposed Transient Voltage Criteria, which they used in their Dynamic Reactive project to evaluate the need for additional dynamic reactive devices in the Houston area. The criteria calls for no voltage collapse, and no more than 1250 MW of Under Voltage Load Shed for certain Category D contingencies. Roy presented the TXU criteria, which calls for determining the dynamic reactive margin of coherent bus groups. The group then discussed several different methods for determining coherent bus groups. The TXU Criteria allows most of the screening analysis to be done in steady-state, with dynamic simulations to be performed only to verify that the reactive margin is adequate. Both criteria appear to be saying close to the same thing, but getting there in a different manner. The difference appears to be how Category D contingencies are handled. Some Category D contingencies have a high enough probability that they should be elevated to Category C, as in the TXU criteria. Others contingencies may have lower probability, but the consequences are severe enough that UVLS amounts should be limited. The TXU criteria would appear to allow no UVLS for selected Category D contingencies, while the CenterPoint criteria would allow up to 1250 MW. Although the DWG could not come to consensus on which criteria to endorse, there was much common ground. The group recognizes that there is an issue with Category D contingencies with severe consequences, for which we need a criteria. More discussion will be needed in order to come up with a way of calculating the allowable UVLS that each member would be comfortable with. DWG agreed that the CenterPoint Dynamic Reactive project is based on sound engineering and is worthy of ERCOT support.
  1. Next meeting: The next meeting has been tentatively scheduled for July 13-14 in Austin.
  1. Adjourned at 3:10 pm.

DWG Minutes 6-30-06Page 111/25/2018