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Power System Incident Report - Gladstone 275 kV Busbar Trip - 03

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					                                    National Electricity Market
                                    Management Company Limited
                                    ABN 94 072 010 327




POWER SYSTEM
INCIDENT REPORT


Gladstone 275 kV Busbar
Trip - 03 September 2008

Prepared by:   System Operations Planning
               and Performance




               Final Version
      Incident Report – Gladstone 275 kV No. 1 Busbar trip - 03 September 2008


      1.   Introduction

      At 15:24:34 hours on 3 September 2008, concurrent tripping of the Gladstone (H007)
      275kV No.1 Busbar and the 812 Gladstone – Bouldercombe 275 kV line was
      experienced during testing of protection systems at Gladstone Power Station.

      The 812 line was re-energised at 16:11 hours from H010 Bouldercombe and placed on
      load at 16:46 hours after the cause was identified.

      Gladstone 275 kV No. 1 busbar was re-energized at 16:53 hrs and all affected
      transmission elements were reconnected to 275 kV No.1 busbar by 17:02 hours.

      This report has been prepared under clause 4.8.15 of the Rules to assess the adequacy
      of the provision and response of facilities & services and the appropriateness of actions
      taken to restore or maintain power system security.

      Information for this report has been supplied to NEMMCO by Powerlink. Data from
      NEMMCO’s Energy Management System has also been used in analysing the event.

      All references to time in this report refer to Eastern Standard Time.

      2.   Summary of Events

      At 15:24:34 hours on 03 September 2008 protection systems at Gladstone Power
      Station operated to trip the H 7 Gladstone substation No. 1 275 kV bus bar and the 812
      Gladstone - Bouldercombe 275kV line. The protection systems that operated were
      associated with Gladstone Generator No.1.

      This occurred while protection checks were being performed by Gladstone Power
      Station, without adequate isolation of Generator No.1 protection systems at Gladstone
      Power Station.

      With the exception of line 812, all the other in service lines1 connected to 275 kV H 7
      Gladstone sub-station remained in service.

      At 16:11 hours 03 September 2008, H 7 Gladstone to Bouldercombe 275kV line was re-
      energised from H 10 Bouldercombe and placed on load at 16:46 hours after the cause
      was investigated. Gladstone 275 kV No. 1 busbar was re-energized at 16:53 hrs and all
      transmission elements were reconnected to 275 kV No.1 busbar by 17:02 hours.




1
 Line 811 was not considered in service due to planned work at the time of this incident. Line 811
was out of service via an open line isolator.


22 December 2008                               FINAL                                      Page 2
      Incident Report – Gladstone 275 kV No. 1 Busbar trip - 03 September 2008


      3.   Protection System Operation

      The transmission network configuration at Gladstone (H007) 275 kV sub-station
      including the status of circuit breakers prior to the event are shown in Figure 1a.




Figure 1a – H007 Gladstone 275kV single line diagram and circuit breaker status
prior to the event.




22 December 2008                         FINAL                                   Page 3
      Incident Report – Gladstone 275 kV No. 1 Busbar trip - 03 September 2008


The 812 Gladstone to Bouldercombe 275kV single line diagram including the status of circuit
breakers prior to the event are shown in Figure 1b.




  Figure 1b – H007 Gladstone to H010 Bouldercombe 275kV (Line 812) single line
                        diagram status prior to the event


      Gladstone Power Station No.1 Generator is protected using high speed primary & local
      back-up protection systems. As part of any planned work on protection systems at
      Gladstone Power Station all potential trip signals from these primary and local back-up
      protection systems to the Gladstone 275kV substation should be isolated to prevent
      incorrect operation of substation equipment.

      The Generator No. 1 protection systems are designed to open circuit breakers 5212 &
      5042. In addition to tripping circuit breakers 5212 & 5042, the generator primary
      protection systems also initiate the associated local backup protection system. If the
      local backup protection system detects that one or both of the circuit breakers have not
      opened to disconnect the generator within the required time, then the local back up
      protection system will trip Gladstone substation 275 kV No.1 busbar and/or circuit
      breaker 8122 (refer Figure 1a) as required.

      On 3 September 2008, Gladstone Power Station’s planned testing of protection systems
      progressed without correctly isolating local back up protection systems even though the
      primary protection system was correctly isolated. The simulated fault resulted in
      operation of the local back up protection systems which sent trip signals to the
      Gladstone Substation.




22 December 2008                          FINAL                                  Page 4
      Incident Report – Gladstone 275 kV No. 1 Busbar trip - 03 September 2008


      When the local back-up protection systems sent trip signals to Gladstone substation,
      the following circuit breakers tripped as designed:

      At H007 Gladstone substation
          o 5412
          o 5212
          o 5422
          o 5222
          o 5252
          o 5262
          o 5042
          o 8122

      At H010 Bouldercombe substation
          o 5052
          o 8122

      Figure 2a and 2b shows the status of the H007 Gladstone 275kV circuit breakers
      after the busbar & line trip.




Figure 2a – H007 Gladstone 275kV single line diagram after the busbar and 812 line
trip.




22 December 2008                         FINAL                                   Page 5
      Incident Report – Gladstone 275 kV No. 1 Busbar trip - 03 September 2008




Figure 2b – H007 Gladstone and H010 Bouldercombe 275kV single line diagram and
circuit breaker status after the 812 line trip.


      4.   Power System Security Assessment

      The cause of the concurrent trip of the No.1 Busbar at H 7 Gladstone and the Gladstone
      - Bouldercombe 275kV line was due to insufficient isolation of local back-up protection at
      Gladstone Power Station while conducting protection testing during a planned outage of
      Generator No.1 resulting in trip signals being sent to H 7 Gladstone switchyard.

      As a result of this event there was no loss of transmission elements other than the trip of
      H 7 Gladstone 275 kV No. 1 Busbar and 812 Gladstone to Bouldercombe line. All other
      transmission lines and transformers at Gladstone substation remained in service via
      coupler circuit breakers and No.2 275 kV Busbar. There was no loss of load as a result
      of this event. There were no other system security implications attributed to this event.




22 December 2008                           FINAL                                    Page 6
      Incident Report – Gladstone 275 kV No. 1 Busbar trip - 03 September 2008


      5.   Actions Taken

      Investigation undertaken by Powerlink immediately after the incident found that there
      were no other system events at the time of this event. The analysis suggested
      insufficient isolation of protection systems of Gladstone Generator No.1 by Gladstone
      Power Station.

      Discussions with Gladstone Power Station staff established that isolation of local back-
      up protection had not been sufficiently completed to prevent trip signals being received
      by H 7 Gladstone busbar No.1 and 812 Gladstone to Bouldercombe line.

      Subsequently, Generator No.1 local back-up protection systems were correctly isolated
      to ensure no further trips would be sent from the power station during the protection
      testing.


      6.   Recommendations

      Stanwell Corporation will review its procedures to be followed when working on
      protection systems at Gladstone power station and report the adequacy of the
      procedures to NEMMCO by the end of March 2009.


      7.   Conclusions

      The trip of the No.1 275kV Busbar at H 7 Gladstone and 812 Gladstone to
      Bouldercombe 275 kV line on 3 September 2008 can be attributed to insufficient
      isolation of local back-up protection systems by Gladstone Power Station.

      The relevant protection systems at Gladstone power station and at H 7 Gladstone 275kV
      substation operated as designed.

      The power system remained secure during the incident and no load was interrupted.




22 December 2008                          FINAL                                  Page 7

				
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