System Protection Schemes (SPS) and Islanding

PSTI, Bengaluru7th August 2013

Definition of System Protection Schemes (SPS)A System Protection Scheme (SPS) or Remedial Action Scheme (RAS) is designed to detect abnormal system conditions and take predetermined, corrective action (other than the isolation of faulted elements) to preserve system integrity and provide acceptable system performance.CIGRE TB 187, June 2001 Earlier known as Special Protection SchemesWhat is special today may be common tomorrow.Other than equipment protectionNow formally known as System Integrity Protection Schemes (SIPS).

What is not SPS?Normal control actions using power electronicsStatic Var Compensators or SVCs, HVDC controls, PSSAuto-reclosing of transmission linesConsidered as part of line protectionEquipment over-load protectionRestoration of equipment

Response-based or Event-based SPSResponse-based: Measured variables cross the trigger value after a contingencyEvent-based: Operate based on recognition of a combination of eventsFaster than response-based but have to be designed for all possible events

Source: CIGRE TB 187

Why System Protection Schemes?Improve power system operationOperate power systems closer to their limitsIncrease power transfer limits while maintaining the same level of system securityTemporary installationsIncrease power system security particularly towards extreme contingencies leading to system collapse.

SPS to counteract power system instability

SPS design criteriaDependability: Operate when required to do so

Security: Not operate when not required

Selectivity: Ability to effect the least amount of action when performing the action

Robustness: Ability to work over the full range of steady state and dynamic conditions

Higher the rule complexity, lower the reliability of performance

SPS design criteriaSPS Control ActionsArmingActivation (detection) controlDetermination of control actionSending trip/activation commandAutomatic arming or disarming is preferable Co-ordination with other SPS or control actions desirableCapacitor or reactor switching vs UFLSUFLS vs under-frequency generator trippingUFLS vs transmission constraintsLoad-shedding vs islanding

SPS Design and Reliability EvaluationSPS event can be classified asDesirable operationUndesirable operation.lesser evil Can either be intended or unintendedFailure to operate.seriousHardware failureFaulty design logicSoftware error Human errorChapter 6 of CIGRE TB 187 covers SPS design aspects and reliability in detail

Institutional co-ordinationSPS involvesLarge number of measurements from various pointsA processing/control centreDiverse elements affected by control actionsSo SPS is a multi-utility level problem

Institutional co-ordinationSource: CIGRE TB 187

Future SPS

Future SPS

Indian experience of SPSA decade of experienceNearly thirty (30) schemes in service at inter-state levelMostly generation 1 schemes (local measurement, local control)A few generation 2 schemes (local measurement, remote actions)Generation 3 schemes (Wide Area Measurements and Wide Area Control) not yet envisaged

Islanding SchemesIslanding is also a category of SPSFrequency based islanding is very commonIslanding based on wide area logic such as angle is yet to be envisagedDie or survive but together has been the normSome re-think after 30th and 31st Jul 2012 Nuclear power stations and metro city islanding has been the norm so far.

References on SPSIndustry Experience with Special Protection Schemes, IEEE-CIGRE Committee Report, IEEE Transactions on Power Systems, Vol 11, No 3, August 1996CIGRE Technical Brochure 187: System Protection Schemes in Power networks, June 2001CIGRE Technical Brochure 200: Isolation and restoration policies against system collapse, April 2002 Global Industry Experiences with System Integrity Protection Schemes (SIPS), IEEE Power System Relaying Committee (PSRC) Working Group C4, October 2009.

IEEE/CIGRE survey 199649 utilities, 17 countries, 111 schemes

IEEE/CIGRE survey 1996

IEEE/CIGRE survey 1996

IEEE/CIGRE survey 1996Operations between 1986-1992 analyzedn1= number of successful operations= 1093n2= number of failures = 36n3 = unsuccessful operations = 20n4 = unnecessary operations = 306Effectiveness index = n1/(n1+n2+n3)Dependability index = n1/(n1+n2)

IEEE/CIGRE survey 1996

IEEE/CIGRE survey 1996

IEEE/CIGRE survey 1996

IEEE/CIGRE survey 1996

IEEE Power System Relaying Committee (PSRC)

IEEE Power System Relaying Committee (PSRC)SIPS purpose

Thank you