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

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)