Review Incident Shin.. - authority for electricity regulation, oman

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2. BEFORE THE INCIDENT In this chapter we discuss the status-quo of the network, organization and staff in relation to the incident. Therefore we are reviewing whether OETC was properly prepared for the fault and its consequences. 2.1. Network The 132 kV Shinas grid station is connected to the Main Interconnected System by one single-circuit 132 kV-line, coming from Wadi Jizzi. In the Shinas grid station two 63 MVA 132/33 kV-transformers feed the 33 kV-network Shinas operated by MJEC. This 33 kVnetwork has interconnections to other 33 kV networks of MJEC. These connections provide a limited back-feed via the underlying 33 kV-network. However, the back-feed is only available after rearrangements of the 33 kV-network and load-shedding in the Shinas area and elsewhere. Therefore the 33 kV-network only provides limited redundancy in the event of the single-circuit 132 kV-line tripping. It can therefore be concluded that the supply to the Shinas 33 kV network does not meet the Security Standard criteria of (n-1). According to the (proposed) Oman Transmission Security Standards 2 , demand groups of 20 to 100 MW should be restored immediately after a first outage ((n-1) Security Standard). Since the load of the Shinas network can reach 65 MW (forecasted load for 2007) loss of a single line, which has to be repaired before the load can be restored, does not meet these Security standards. The (proposed) Security standards in Oman are similar to Security standards in many Grid Codes. However, in contrast to the Oman Transmission Security Standard, some grid codes and/or design standards accept losing load if it is only for automatic or manual switching activities taking a few minutes. E.g. the GB Security and Quality of Supply Standard specifies that for interruptions of loads (‘group demands’) up to 60 MW, two-thirds of the load has to be restored within 15 minutes. Nevertheless, since there are no possibilities to quickly restore the load in the Shinas area by fast switching actions, the network design would also not have met this type of standard. 2 See section 6.2 of the ‘Report on capital and operating expenditure requirements for the Oman electricity Transmission Company for the period 2006 - 2010’, by SKM, July 2006. Review Incident Shinas August 2007 6 09.10.2007 vs. 2 (final)
We were told that the investment in a second circuit to the Shinas grid station was already planned during the time that the Ministry of Housing Electricity and Water was the operator of the transmission network, ie there were plans for a second circuit to Shinas before 1 May 2005 3 . According to OETC’s investment plan for 2006 4 a second 132 kV-circuit to the Shinas grid station had been planned for construction in 2006. We understood from OETC 5 that this project had been delayed because it was combined with the investment in a new grid station in Liwa, which increased the efficiency of this investment. OETC confirmed that the construction of a second circuit to Shinas is now in the tendering phase. However, we have not seen any proof of this. It can be concluded that if there had been a second 132 kV-circuit to Shinas, the fault would not, under normal operating conditions, have caused an outage since the second feeder would have been capable of supplying the entire load. For the peak demand of the Shinas area (65 MW forecasted for 2007) this situation is unacceptable according to international and Oman standards. This has been recognized by OETC and its predecessors for many years (before 2005) and KEMA strongly recommend that the contract to provide for n-1 is implemented on an expedited basis. 2.2. Preparedness for a fault in the Wadi Jizzi – Shinas line The reason why, in general, the (n-1) criterion is applied is that there is a reasonable risk that faults in lines, transformers, generators etc will occur. This risk combined with the damage of losing load results in the need to invest to provide additional redundancy of system elements e.g. lines, transformers etc. Security Standards allow for and even require large investments to provide (n-1) security in transmission networks. Following this logic, situations in which these standards are not met should be considered very seriously. For these situations in which a single fault will lead to an outage with significant loss of load for a long duration (the repair time) there should be detailed and comprehensive plans. Since it was recognized by OETC (see section 2.1) that the (n-1) security criterion was not met for the Wadi Jizzi – Shinas line, then there should have been a plan in place to deal 3 1 May 2005 is the date OETC took over the responsibility of the transmission network. 4 See section 7.2 of the ‘Report on capital and operating expenditure requirements for the Oman electricity Transmission Company for the period 2006 - 2010’, by SKM, July 2006. 5 Interview on 1 September 2007. Review Incident Shinas August 2007 7 09.10.2007 vs. 2 (final)
Page 1 and 2: Review Incident Shinas area 27-29 A
Page 3 and 4: necessary safety measures such as l
Page 5: 1. INTRODUCTION On 27 August 2007,
Page 9 and 10: contract with Civil Co (we have onl
Page 11 and 12: One set of procedures is about trai
Page 13 and 14: crucial for the LDC staff to be bac
Page 15 and 16: 4.3. Spare parts Since spares were
Page 17 and 18: 4.6. Incident center As discussed i
Page 19 and 20: 5. CONCLUSIONS Based on the review

Review Incident Shin.. - authority for electricity regulation, oman

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