Security Policy Review: Credible Event Management Scope and Methodology Draft for Industry 2014
Version Date Change 1 26/03/2014 Draft for industry Position Date Prepared By: Reviewed By: Ina Ilieva, Senior Investigations Engineer Mohamed Zavahir, Investigations Manager IMPORTANT Copyright The concepts and information contained in this document are the property of Transpower New Zealand Limited. Reproduction of this document in whole or in part without the written permission of Transpower New Zealand. Contact Details Address: Transpower New Zealand Ltd 96 The Terrace PO Box 1021 Wellington New Zealand Telephone: +64 4 495 7000 Fax: +64 4 498 2671 Email: Website: system.operator@transpower.co.nz http://www.systemoperator.co.nz
Table of Contents 1. Purpose... 4 2. Background... 5 3. Methodology... 6 4. 4.1 Scope... 7 Credible events identification... 7 4.2 4.3 4.4 4.5 4.6 Risk analysis... 8 Credible Event Classification and Management... 8 Assumptions... 9 Documentation... 10 Project Schedule... 10 *Milestone dates will be the last working day of the calendar month... 11 3
1. PURPOSE This paper seeks to advise industry participants of the System Operator s intended review of the Security Policy: Credible Event Management. It describes the proposed scope of work and the intended methodology as well as the intended outcomes and timetable. 4 Industry participants are invited to provide comments and feedback to the System Operator onl aspects of the System Operator s intended work and actions as outlined in this paper.
2. BACKGROUND As part of the System Operator s Policy Statement, the Security Policy identifies events that could occur within the power system that, if not appropriately managed, could result in wide spread, or cascade, failure within the power system. The credible events covered in system operation, and the associated control for each event, have significant implications to consumers through price and security of supply outcomes. They are also of interest to a wide range of stakeholders including the Electricity Authority (EA) as industry regulator (in respect of the wholesale market and transmission), market participants and asset owners such as generators, distributors and Transpower. 5 The System Operator has the obligation to review its Credible Event Management not less than once in every five year period. This review obligation is expressed in the Policy Statement. The last substantive review of the events included in Credible Event Management occurred in 2009. This 2014 review will in considering the system topology, equipment commissioned, existing asset performance and any new regulation also take into account where possible the reliability, efficiency and competition impacts to the power system.
3. METHODOLOGY The Security Policy Review: Credible Event Management review will use the risk management framework described in AS/NZS ISO 31000:2009 Risk Management Principles and Guidelines. The System Operator will review and assess the credible events described in Section 12.1 of the Policy Statement 1. The risks arising from these events will then be assessed, analysed and evaluated in the context of the System Operator s Principle performance Obligations (PPOs). 6 Any additional or new risks identified in the course of the studies will be also be analysed and evaluated. The risk analysis will be performed according to the process described in Section 5 of the Risk Management standard mentioned above and as shown 1n Figure 1-2 below. Risk treatment plans and a draft of the Security Policy will be presented for feedback to industry participants. Figure1-2 Risk Management process 1 The Policy Statement can be found at http://www.systemoperator.co.nz/market/policy-statement
4. SCOPE 4.1 CREDIBLE EVENTS IDENTIFICATION The Credible Event Review completed in 2009 identified the following credible events (each an event ) for which mitigation measures were identified, classified and implemented: The loss of one of the following power system components: a generating unit; or a transmission circuit; or an HVDC link pole; or an interconnecting transformer (110 kv or 220 kv); or. a busbar (220 kv, 110 kv or 66kV); or large load or load blocks; or reactive injections, both when provided as an ancillary service or when available from transmission assets: 7 The simultaneous loss of two or more of any of the components listed above; The close consecutive loss of two or more of any of the components listed above; The loss of both transmission circuits of a double circuit line; The loss of the HVDC link bipole: Over the past five years, the system operator has identified the following new risks that may arise on the power systems and these risks should be studied, analysed and evaluated: Risks associated with the possible non-compliance with the proposed fault ride through envelope 2 Risks arising from system faults which could have stability impacts (such as AC faults, DC faults, etc) Risks associated with or as a result of the application of a particular mitigation measure (such as AUFLS operation, SPS operation, system islanding, etc) Risks associated with the mode of operation of specific equipment, e.g. the frequency keeping control (FKC) of the HVDC link, the Multiple Frequency Keeping tool (MFK), etc. The System Operator intends to study and analyse other events and uncertainties with a potential negative impact on the system,e.g. gas contingency, loss of a whole substation, a natural disaster, etc. The analysis of such events will be limited to evaluation of the impact and high level proposal for an emergency response. 2 The Fault Ride Through (FRT) investigation from 2010 proposed that an island-based voltage FRT envelope be implemented for the North and South Islands. The EA has proposed code changes to for the voltage FRT envelope to be implemented. More information can be found at http://www.ea.govt.nz/our-work/consultations/psocq/generation-fault-ride-through/
Historic data, operational experience and network analysis will be used to assess the likely occurrence of the risks. The likely duration of the events will be extrapolated from historic data. 4.2 RISK ANALYSIS A risk analysis of the identified events will, in general, include the following tasks: 8 consideration and evaluation of the consequences of a risk, or a combination of risks, if not managed/mitigated; confirmation of any applicable mitigation measures, existing and alternative; evaluation of the mitigation measures, including any subsequent risks arising from the mitigation measure itself, including but not limited to incorrect application or failure; high level cost evaluation of the consequences of and management of the identified risks and of the various mitigation measures; identification of potential secondary risks which will need further studies Identified credible event risks will be considered mitigated when the following criteria are met: Voltages are within the limits of the Electricity Industry Participation Code ( Code ) Frequency is within the limits of the Code Assets do not overload beyond their specified post-contingency offload limits No instability occurs No cascade failure occurs 4.3 CREDIBLE EVENT CLASSIFICATION AND MANAGEMENT The risk analysis in section 4.2 and the identified mitigation measures will be the basis for further review of event categorisation. In the Policy Statement, credible events are classified according to the mitigation measures applied. The classification is based on the way these events are managed preevent. There are two broad classification groups: Contingent events are events which are managed pre-event and no unplanned load shedding is expected to occur. These measures include: Use of off-load time or emergency rating Procurement of instantaneous reserves Procurement of over frequency arming Generation constraints Wider voltage agreement Automatic under voltage load shedding, or AUVLS Automatic switching of reactive devices
Reduced security Load arrangements to manage load Inter trips, run-backs, special protection schemes (SPS) Grid reconfiguration A combination of the above Extended contingent events are events which are not managed pre-event and include post-event planned load shedding. The System Operator manages such events with any of the mitigation measures applied for contingent events plus: Automatic under frequency load shedding, or AUFLS Stability events are managed pre-event by maintaining identified transient and dynamic stability limits. Unplanned load shedding may be used. 9 For other events, no planned controls have been identified other than load shedding, AUFLS and other emergency or restoration procedures. The analysis, in Section 4.2, of the event management will be performed taking into account and considering reliability and efficiency. 4.4 ASSUMPTIONS The Security Polici Review: Credible Events Management review will be based on the following assumptions: that asset owners, ancillary service providers and other service providers to the System Operator meet and comply with all contractual and Code obligations; assets perform as anticipated, asset owners have conveyed this information to the System Operator and the System Operator is using this information. This relies on asset owners comprehensively understanding the performance of their assets; and the security standard to be met is as set out in Part 7 and Part 8 of the Code. More specifically the Credible Event Management review assumes: the Automatic Under-Frequency Load Shedding (AUFLS) scheme operates as anticipated; demand blocks exist at all times and load is shed within the prescribed timeframe. The existing 2x16% scheme will be compared with the proposed new AUFLS scheme of 4x blocks 3 ; the power system remaining stable after the operation of the AUFLS scheme; 3 There is a proposal that a new AUFLS scheme consisting of four blocks sized in 10%:10%:6%:6% ratio; the last block will be triggered by a df/dt relay. During the event review, the new AUFLS block arrangements of block size and tripping frequency will be assessed along with the existing AUFLS blocks of 2x16%; http://www.ea.govt.nz/our-work/consultations/pso-cq/efficient-procurement-ofextended-reserves-second-consultation/
10 the Automatic Under-frequency Load Shedding (AUFLS) scheme operating as anticipated; demand blocks exist at all times asset capability statements fairly reflecting asset capability and performance; the System Operator has incorporated Asset Capability Statement (ACS) data into system models; system models adequately represent the actual power system and include the confirmed significant asset commissionings expected to be completed by the end of June 2015; expected co-ordination between asset owner protection schemes exists; offered transmission, generation, ancillary services, and special protection schemes being physically available and operational; asset owners and ancillary service providers complying with dispatch instructions; and that assets remain connected and will contribute to maintenance or restoration of power quality while power quality remains within Asset Owner Performance Obligations limits specified in the Code or as exempted or granted dispensations. 4.5 DOCUMENTATION Documentation to be published includes: the scope and methodology; Event risk assessment report including o Event analysis o Event management o High level cost estimates of the event management options Optimal risk management mitigation measures report a draft new Credible Event Management Policy with proposed clauses for incorporation within the Policy Statement; and The final Credible Event Management Policy with proposed clauses for incorporation within the Policy Statement by the end of June 2015. 4.6 PROJECT SCHEDULE The Credible Event Management review is expected to be completed by December 2014. To allow for review and stakeholder comment a draft report for participant review is expected to be issued during November 2014. Defining tasks and the associated project milestones will enable project progress to be monitored and indicate resource requirements during different phases of the project. Project phases are indicated in Figure 1.2, milestone dates are given in Table 1.
Figure 4-1 Project Tasks 11 Table 1 Project Milestones Date * Milestone Description 26 Mar 2014 Phase 1: Draft scope and methodology released to Industry for feedback 30 April 2014 Phase 1: Scope and methodology completed 30 June 2014 Phase 2: Identification and analysis of credible events completed 15 Aug 2014 Phase 3: Optimal means of credible event management completed 15 Oct 2014 Phase 4: Analysis, conclusions and recommendations drafted 15 Nov 2014 Phase 5: Draft Review released to Industry for feedback 31 Dec 2014 Phase 6: Security Policy Review: Credible Event Management Review completed Incorporation of Event Management Policy into draft annual Policy Statement Review 31 Mar 2015 Event Management Policy submitted to the Electricity Authority as part of the draft Policy Statement