Basslink Incident Report
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TRIP OF TRANSMISSION LINES IN TASMANIA FOLLOWED BY THE LOSS OF BASSLINK ON 10 AND 16 DEC 2014, AND 23 FEB 2015 AN AEMO POWER SYSTEM OPERATING INCIDENT REPORT FOR THE NATIONAL ELECTRICITY MARKET Published: MAY 2015 TRIP OF TRANSMISSION LINES IN TASMANIA FOLLOWED BY THE LOSS OF BASSLINK ON 10 AND 16 DEC 2014, AND 23 FEB 2015 IMPORTANT NOTICE Purpose AEMO has prepared this document to provide information about this particular Power System Operating Incident. Disclaimer This document or the information in it may be subsequently updated or amended. This document does not constitute legal or business advice, and should not be relied on as a substitute for obtaining detailed advice about the National Electricity Law, the National Electricity Rules, or any other applicable laws, procedures or policies. AEMO has made every effort to ensure the quality of the information in this document but cannot guarantee its accuracy or completeness. Accordingly, to the maximum extent permitted by law, AEMO and its officers, employees and consultants involved in the preparation of this document: Make no representation or warranty, express or implied, as to the currency, accuracy, reliability or completeness of the information in this document; and Are not liable (whether by reason of negligence or otherwise) for any statements or representations in this document, or any omissions from it, or for any use or reliance on the information in it. VERSION RELEASE HISTORY Version Date By Changes Checked by Authorised by 2 14 May 2015 S Darnell Summary in Section 5.1 amended M Miller M Miller to better reflect report content 1 12 May 2015 S Darnell FINAL M Miller M Miller © 2015. The material in this publication may be used in accordance with the copyright permissions on AEMO’s website. Australian Energy Market Operator Ltd ABN 94 072 010 327 www.aemo.com.au [email protected] NEW SOUTH WALES QUEENSLAND SOUTH AUSTRALIA VICTORIA AUSTRALIAN CAPITAL TERRITORY TASMANIA TRIP OF TRANSMISSION LINES IN TASMANIA FOLLOWED BY THE LOSS OF BASSLINK ON 10 AND 16 DEC 2014, AND 23 FEB 2015 CONTENTS 1. OVERVIEW 4 2. THE INCIDENTS 5 2.1 Trip of Waddamana–Lindisfarne No.2 Line and Basslink 5 2.2 Trip of Gordon – Chapel Street No.1 and No. 2 lines and Basslink 5 2.3 Trip of Gordon – Chapel Street No. 2 Line and Basslink 6 2.4 Recent Transmission faults that did not trip Basslink 6 3. TECHNICAL REVIEW 7 3.1 Commutation Failure 7 3.2 Industry Practice 8 3.3 Tasmanian Transmission Faults and Coincident Basslink Trips 9 4. POWER SYSTEM SECURITY 10 4.1 Trip of WA-LF No.2 line and Basslink on 10 December 2015 10 4.2 Trip of GO-CS Lines and Basslink on 16 December 2015 10 4.3 Trip of GO-CS No.2 Line and Basslink on 23 February 2015 14 5. CONCLUSION 15 5.1. Preliminary Findings 15 5.2. Consideration of additional short term measures 15 5.3. Program for detailed investigation 15 5.4. Longer term solutions 16 5.5. Incorrect reclassification 16 LIST OF SUPPORTING DOCUMENTS 17 ABBREVIATIONS 18 APPENDIX A. POWER SYSTEM DIAGRAM 19 © AEMO 2015 3 TRIP OF TRANSMISSION LINES IN TASMANIA FOLLOWED BY THE LOSS OF BASSLINK ON 10 AND 16 DEC 2014, AND 23 FEB 2015 1. OVERVIEW This preliminary report reviews three similar power system operating incidents that occurred in Tasmania on 10 December 2014, 16 December 2014 and 23 February 2015. These incidents involved the trip of transmission lines in Tasmania followed by the trip of Basslink.1 AEMO is required to review and report on the two incidents in December 2014 as they comprised non-credible contingencies under the National Electricity Rules (NER).2 The third event was included in the review because of its similar technical nature. Specifically in relation to the reviewable incidents, AEMO is required to assess the adequacy of the provision and response of facilities and services and the appropriateness of actions taken to restore or maintain power system security3 and to give details of the assessment and application of the reclassification criteria to each non-credible contingency event.4 AEMO’s preliminary findings are that: The three faults on the 220kV system were cleared in accordance with the System Standard for fault clearance times.5 The Basslink control and protection systems operated as designed. The unbalanced nature of the faults initiated commutation failure on the inverter at Georgetown, which is a normal occurrence on a temporary basis during faults in the Tasmanian AC system. The high voltage direct current (HVDC) link tripped because the commutation failures were sustained. The report also sets out the program for the next stage of detailed investigations. Section 2 of this report describes the three incidents. Section 3 provides a technical assessment of the incidents, and Section 4 sets out AEMO’s assessment of power system security over the course of the incidents. AEMO’s preliminary conclusions are summarised in Section 5, together with the program for the next stage of detailed investigations. This report is based on information provided by TasNetworks6, Basslink Pty Ltd (Basslink)7, and AEMO. National Electricity Market time (Australian Eastern Standard Time) is used in this report. 1 Basslink is a direct current (DC) transmission connection (undersea cable) that electrically connects the Australian mainland to Tasmania. 2 NER Clause 4.8.15(a)(1)(i) and AEMC Reliability Panel Guidelines for Identifying Reviewable Operating Incidents. 3 NER Clause 4.8.15 (b) 4 NER Clause 4.8.15(a) 5 NER Clause s5.1a.8 6 TasNetworks is the Transmission Network Service Provider TNSP in Tasmania. 7 Basslink Pty Ltd is the operator of the Basslink power cable that connects Victoria to Tasmania. © AEMO 2015 4 TRIP OF TRANSMISSION LINES IN TASMANIA FOLLOWED BY THE LOSS OF BASSLINK ON 10 AND 16 DEC 2014, AND 23 FEB 2015 2. THE INCIDENTS Three similar power system operating incidents occurred in Tasmania during December 2014 and February 2015. The three incidents involved the trip of 220 kV transmission lines, the trip of Basslink and the loss of customer load. The trip of Basslink for transmission faults elsewhere in Tasmania is an unexpected event and is identified in power system security terms normally as a non-credible event.8 See Appendix A for a power system diagram illustrating the incidents. 2.1 Trip of Waddamana–Lindisfarne No.2 Line and Basslink On Wednesday 10 December 2014, at 1444 hrs, one phase of the Waddamana - Lindisfarne No.2 220 kV transmission line (WA-LF No.2 Line) was opened at each end in response to a fault condition. Single phase auto-reclose (SPAR) installed on this line then immediately auto- reclosed, successfully, to return the line to service. The trip event was due to a transitory fault. During the event, Basslink tripped at the Tasmanian end 114ms after the fault. The trip of Basslink as a consequence of the fault on WA-LF N.2 line was unexpected. At the time Basslink was importing 443 MW into Tasmania. As a result of the Basslink trip, the Frequency Control System Protection Scheme (FCSPS9) operated and disconnected 383 MW of customer load. This was an expected event designed to mitigate the impact on power system frequency caused by the loss of Basslink power transfer. The loss of customer load occurred in accordance with commercial arrangements. Customer load restoration began at 1537 hrs and was complete by 1617 hrs. The WA-LF No.2 Line remained in service following the auto-reclose sequence, and Basslink returned to service at 1700 hrs the same day. Basslink investigated the trip of the interconnector and found that Basslink operated as per design. TasNetworks investigated the fault event on the WA-LF No.2 line and found that the phase tripped as a result of a single phase to earth fault. The fault was cleared in 80ms, which is within the mandated timeframe10, and successfully auto-reclosed via SPAR. TasNetworks considers that the fault event was most likely as a result of a lightning strike, as there was lightning activity in the area at the time. TasNetworks patrolled the line by air the following day but did not identify an obvious fault location. 2.2 Trip of Gordon – Chapel Street No.1 and No. 2 lines and Basslink On Tuesday 16 December 2014 at 0746 hrs, one phase in each of the Gordon – Chapel Street No.1 and No.2 220 kV transmission lines (GO-CS Lines) tripped as a result of a single phase fault. Each phase was tripped at the Gordon and Chapel Street ends and both phases auto-reclosed successfully. The trip was the result of a transitory fault and the auto-reclose was an expected event. 8 NER Clause 4.2.3 – Credible and non-credible events: AEMO Power system Security Guidelines Section 10 – Definition of a non-credible event. 9 The FCSPS is designed to disconnect a predetermined load for a trip of Basslink when it is importing into Tasmania. This operation is required to maintain power system frequency following the trip of Basslink. Without the FCSPS the frequency in Tasmania would fall below the minimum operating standard following a Basslink (importing) trip. 10 NER Schedule 5.1a System Standards Clause S5.1a.8 – Fault clearance times. © AEMO 2015 5 TRIP OF TRANSMISSION LINES IN TASMANIA FOLLOWED BY THE LOSS OF BASSLINK ON 10 AND 16 DEC 2014, AND 23 FEB 2015 During the event, Basslink tripped at the Tasmanian end 112ms after the fault. The trip of Basslink as a consequence of the effect of the faults on the GO-CS lines was unexpected.