Loss of Solar Resources During Transmission Disturbances Lou Fonte Sr. Advisor, Grid Assets July 24, 2017
Agenda Time Item Speaker 10:10 Introduction 10:15 Review of transmission events 10:25 Overview of Current Issues Lou Fonte 10:35 Formation of NERC Task Force Sr. Advisor 10:45 Review of NERC Report (6/17) Grid Assets Dept. (916) 608-1290 10:55 Review of NERC Advisory (6/20/2017) Lfonte@caiso.com Summary of CAISO short, intermediate 11:05 and long term actions 11:10 Questions Page 2
Helpful Acronyms GO Generator Owner GOP Generator Operator PU Per Unit OEM Original Equipment Manufacturer Page 3
Review of Transmission Events • The CAISO has observed large blocks of solar PV generation disconnect from the system, sometimes for extended periods of time, during the normal clearing of high voltage transmission system faults • Between the months of August 2016 and February 2017 there have been eight transmission system faults that occurred in the southern California area, that resulted in the unanticipated loss of up to 1200 MW of inverter based generation • All transmission line faults cleared in four cycles or less (normal high speed tripping) Page 4
Summary of Transmission System Events Event Date / Time Voltage kV Gen Lost 1 8/16/16 1145 500 1178 MW 2 8/16/16 1404 500 234 MW 3 8/16/16 1513 500 311 MW 4 8/16/16 1519 500 30 MW 5 9/06/16 1317 500 755 MW 6 9/12/16 1740 500 62 MW 7 11/12/16 1000 230 231 MW 8 2/06/17 1213 500 740 MW Note: all faults cleared within four cycles, generation loss is approximate. Page 5
Overview of Current Issues 1. CAISO, together with WECC, NERC, PTOs, GOs and Inverter OEMs, needs to fully identify the causes of the generation drop 2. CAISO, together with the inverter OEMs and GOs, needs to identify measures to remediate solar PV generation equipment 3. CAISO needs to evaluate its exposure to unplanned generation loss both before and after the solar PV equipment undergoes remediation 4. CAISO (as a registered BA) needs to report back to NERC per the Alert issued June 20, 2017 Page 6
Formation of NERC Task Force 1. SCE initiated an investigation into the loss of solar PV generation 2. SCE asked the CAISO to participate in its investigation 3. Upon review and analysis of events, SCE/CAISO jointly brought their concern to WECC and NERC 4. NERC agreed to form a task force to investigate 5. The NERC task force published its findings and recommendations in a report entitled “1,200 MW Fault Induced Solar Photovoltaic Resource Interruption Disturbance Report”, June 2017 and is available on NERC’s web site: http://www.nerc.com/news/Headlines%20DL/Inverter%20060817.pdf Page 7
Review of NERC Resource Interruption Disturbance Report Key Finding : Inverters that trip instantaneously based on near instantaneous frequency measurements are susceptible to erroneous tripping during transients generated by faults on the power system Recommendation : Add time delay to inverter control settings to avoid erroneous tripping, this change will allow the inverter to “ride through” the transient / distorted waveform period without tripping Key Finding : The majority of inverters are now configured to cease current injection for voltage > 1.1 PU or < 0.9 PU Recommendation : Inverters that momentarily cease current injection should be configured to restore output with a delay no greater than five seconds Page 8
Review of NERC Resource Interruption Disturbance Report – Additional Recommendations In depth analysis of momentary cessation with higher penetrations of inverter connected resources is needed to determine if this should continue for voltage less than 0.9 PU or greater than 1.1 PU A NERC advisory should be issued to GOs and GOPs to ensure they are aware of recommended changes to inverter settings. The alert should include BAs and RCs to assess the reliability risk of solar PV momentary cessation and take appropriate measures. NERC Alert published at: http://www.nerc.com/pa/rrm/bpsa/Alerts%20DL/NERC%20Alert%20Loss%20of% 20Solar%20Resources%20during%20Transmission%20Disturbance.pdf Page 9
Review of NERC Advisory Recommendation 1 : GOs and GOPs should ensure that inverter controls will not trip due to erroneous instantaneous frequency measurements during power system transients Recommendation 2 : Following momentary cessation, GOs and GOPs should ensure the time to restore output of the inverter to the state prior to abnormal voltage conditions is as soon as practical but no greater than five (5) seconds Recommendation 3 : RCs and BAs should identify which plants are left unmitigated, consider the potential loss of these resources during transmission faults, and take appropriate mitigating measures Note: reporting required by midnight eastern August 31, 2017 Page 10
Summary of CAISO Short Term Action Items • Enhance existing generation interconnection process: – Update the generator interconnection request (IR) form to include detailed inverter information ( completed ) – Modify the protection review of the NRI process to include review of inverter settings ( completed ) • File request for clarification of PRC-024 ( completed ) • Work with NERC/WECC team to investigate and identify root cause(s) of inverter cessation and inverter tripping ( partially complete – a very small percentage of inverters tripped on DC overcurrent – root cause still not identified, investigation is ongoing) Page 11
Summary of CAISO Intermediate Action Items • Temporarily increase contingency operating reserves • Work with inverter OEM to modify frequency tripping settings, voltage block settings, and track progress completion • CAISO surveying generators and building a database of inverter (asynchronous) generators, to include details on inverter models and control settings. The CAISO needs and requests the cooperation and assistance of the GOs and GOPs with this! • Verify that inverters that use momentary cessation have control settings to return to ‘normal’ service within five seconds, assuming remediation is required or can be accomplished • Re-evaluate need for additional contingency operating reserves after completing asynchronous generation database and evaluating all inverter control settings Page 12
Summary of CAISO Long Term Action Items • CAISO will continue to actively participate in and support the Phase 2 NERC task force investigation 1. Scope and conduct various transmission planning and stability studies to support the phase 2 NERC task force 2. Publish results of NERC task force results and recommendations • Support the effort to either develop a new NERC controls based Standard, or revise existing current Standards, to address the recommendations identified in the NERC report • Implement the new or revised Standard(s) when available • Continue to work with inverter OEMs, GOs and GOPs to maintain the quality of the asynchronous generator database and also investigate new “events” Page 13
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