WGR Ramp Rate in Nodal:“As High as Possible” Mike Grimes for QMWG Meeting 10 August 2009
WGR Ramp Rate in Nodal:“As High as Possible” • SCED computes new base point assuming ramp is limited to registered ramp rate • WGR Base point = telemetered output, not an issue absent curtailment, i.e. new base point from SCED • RARF instruction is: WGRs should register “highest possible ramp rate” • Implication is that WGRs are expected to move to new base points as quickly as possible • Frequency excursions due to varying ramp rates are managed by QSEs providing A-S, via LFC
A-S provided: Reg Up, Generation Responsive, Non-Spin Generation Generation Increase Increase Increase HASL - - - HDL Offer Curve Generation Ramp Ramp Ramp Rate Rate Rate Current Telemetry Quantity LDL Generation Generation LSL LSL HSL HSL Decrease Decrease LASL - - - Generation Ancillary Decrease Services LSL - - - provided: Reg Down Time 0 5 Minutes SCED’s New Base Point Assumes Ramp Rate HDL = Min (POWERTELEM + (SURAMP * 5), HASL), Where SURAMP effectively = Ramp Rate [in MW/minute]
SCED Assumes a Ramp RateTracks Output Every 4 Seconds • Required to set HSL = telemetered output each cycle (nominally 5 minutes) • NP 220.127.116.11 (3) “For each Wind-powered Generation Resource (WGR), the QSE shall set the HSL to the output capability of the facility based upon all available units and the current measured wind speed (HSL must be equal to or greater than the latest telemetered net real power of the WGR).” • SCED uses registered/updated ramp rate as an input when choosing a new base point • 2 cases of interest: • Curtailment/base point < HSL (or RPP) • Release from curtailment/ base point = RPP
Background - SCED Uses RARF Ramp Rate as Input • Required: Generation Resource Parameters (NP 18.104.22.168) • (1)(f) Normal Ramp Rate curve; • (1)(g) Emergency Ramp Rate curve; • QSEs must update Resource Status (NP 6.4.5) • (1) ERCOT shall use the telemetered Resource Status for all applications requiring status of Resources during the Operating Hour, including SCED, Load Frequency Control (LFC), and Network Security Analysis processes. QSEs shall provide ERCOT with accurate telemetry of the current capability of each Resource including the Resource Status, Ramp Rates, HSL, and LSL and a text reason for any Resource where a Ramp Rate is deviating from a standard Ramp Rate curve for the Resource, or the HSL is less than, or LSL is greater than, the normal high and low limits set in Section 3.7.1, Resource Parameter Criteria.
Background – RARF Instructions • Ramp rate curves are step functions in the up and down directions at ten MW break points. All ramp rate values, including downward rates, should be entered in the RARF as positive values. • The values submitted in the RARF are used to build the ramp rate step curves, and should not be used as tools to restrain the operating range of the unit or configuration. The curves essentially range from zero to infinity, but realistically, the curves are limited to LRL and HRL.
Background – RARF Q&A 11 November 2007 • Ramp rates per MW value? • Ramp rate CURVE is intent – points on curve provide reasonable data for dispatching different MW’s at different curves. • Ramp Rate? • ERCOT not requesting all 5 requesting range/curve to cover your full operating range. • ‘Generation’ tab, why are there different MW values for Ramp Rate? • This is for the ramp rate curve. If you are at Low Sustainable Limit (LSL), your ramp rate may be 5 MW p/min, but a higher limit may be able to ramp faster. Once you get to the High Sustainable Limit (HSL) you may have to ramp slower. • What is a normal ramp rate for wind, since it depends on the availability of wind to be able to generate? • ERCOT desires the highest possible ramp rate from the resource under any circumstances (validity check only, not used for dispatch).
Background – RARF Q&A 12/12/07; Repeated in WGR RARF Workshop 24 March 2008 • Does ERCOT want the ramp rate for conditions of a zero wind speed (zero generation) to the highest wind speed on the manufacturer’s curve (nameplate capacity)? • ERCOT desires the highest possible ramp rate from the resource under any circumstances in order to be able to validate data (not used for dispatch). • For the "Normal Ramp Rate Curve" on the "Combined Cycle" tab, does ERCOT expect to see the ramp rate from LSL to HSL or the ramp rate in the start-up period? • ERCOT desires the ramp rate curve at Low Reasonability Limit (LRL) to the High Reasonability Limit (HRL). • For Ramp Rate Curves, the ramp rate varies in different operational scenarios, such as winter, summer etc. What does "Normal" mean? • ERCOT desires the ramp rate curve from the Low Sustainable Limit (LSL) to the High Sustainable Limit (HSL) and can be entered in 5-pairs (at different MW levels). If there are significant changes in operational conditions (derating, unplanned outages, seasonal configuration changes) the ramp rate curves can be updated with the QSE providing a reason code- but this should be only a few times per year.
Background – RARF Q&A 17 April 2008 • Regarding ramp rates for a wind farm: There are internal turbine limits set – regardless of ramp requests. Should I use these for my limits? • If you have a known limit, please use it. • How is ERCOT using the High Reasonability Ramp Rate Limits in comparison to the Emergency Ramp Rate curves? EDS appears to be using the lowest value of the Emergency Ramp Rate curves as limits. • Similar to the HRL and LRL, the HRRRL and LRRRL should be “out-of-bounds” values for the Ramp Rate curves submitted in the RARF and by the QSE. ERCOT is researching this question. The HRL, LRL, HRRRL, and LRRRL are not used operationally – they are used only to validate submittals. • Responsive Reserve limit is the minimum of 20% of the HSL or 10 times the minimum emergency ramp rate. ERCOT is reviewing the use/accuracy of the minimum emergency ramp rate in this situation
Background – Updated Desired Base Point“expected MW output of a Generation Resource ramping to a SCED Base Point” • SCED sees output every 4 seconds, and uses that data to issue “desired” BPs, but only to QSEs offering A-S. • Ca. January 2007 “SCED Base Point Dispatch” white paper recommends telemetry of “updated base points” every 4 seconds via LFC • Intended to address frequency deviation resulting from units ramping at different rates • Discusses ramping over 4 minutes, so units get to new base points before end of 5 minute interval • Benefit: minimize regulation A-S • Approved as part of NPRR 049 for QSEs providing A-S • “Based on the ACE MW correction, the LFC issues a set of control signals every four seconds to each QSE providing Regulation and, if required, each QSE providing Responsive Reserve.” (NP 22.214.171.124.1(4))