Transmission System Performance in Oman

05-01-2022

The Oman Electricity Transmission Company (OETC) is authorized to undertake all the regulated activities of electricity transmission system and load dispatch in northern and southern Oman. It comprises the Main Interconnected Transmission System (MITS) centered in northern Oman that has three operating voltages i.e. 400 kV, 220 kV and 132 kV and the Dhofar Transmission System (DTS) in southern Oman that has only one operating voltage i.e. 132 kV. The DTS only became under the responsibility of OETC in 2014.

The MITS transmission system comprises some 81 grid stations extending across the whole of northern Oman, interconnecting generators and bulk consumers of electrical energy located in the Governorates of Muscat, Batinah South, Batinah North, Dhahirah, Buraimi, Dakhliyah, Sharquiya South and Sharqiya North. The MITS overhead line transmission system is 6443.65 km (4003.9 miles) in length.

The Dhofar Transmission System (DTS) in southern Oman based in the Dhofar Governorate, is a much smaller transmission system operator having eight grid stations and a 132 kV overhead transmission line network 501.8 km (311.8 miles) in length. At present, there is no electrical interconnection between the MITS and DTS transmission systems.

The MITS 400 kV Transmission System

Oman’s first section of the 400 kV transmission system was erected by the OETC to interconnect the large gas-fired power plant at Sur (2000 MW) in northern Oman to the MITS. One of the 400kV, 250 km (155 mile) double-circuit overhead lines was used to supply energy to the 400 kV New Izki Grid Substation. Additionally the, OETC has constructed 100 km (62 miles) 400kV double-circuit overhead lines between Sur PS and Jahloot; between Ibri and the New Izki Grid Substation (264 km-164 miles) and Sohar Free Zone and the Sohar Interconnection Substation (34 km- 21 miles). Furthermore, a one 400kV 100 km (62 miles) double-circuit overhead line between the New Izki Grid Substation and Misfah will be commissioned in 2020.

Load flow studies undertaken during the design stage confirmed that the voltage levels at some of the MITS Grid Substations stations could reach high values which exceeded the Transmission Security Standard (± 5% at 400kV) during periods of off-peak demand. This being caused by the reactive power generated by 400 kV lines. Moreover, the voltage at a number of Grid Substations reached values in excess of 12.75% at 400 kV and 10.6% at 220 kV during the off-peak demand period. These excessively high values can even lead to difficulties in synchronizing the 400 kV transmission lines.

Furthermore, due to light loading of the 400kV long overhead transmission lines supplying the New Izki Grid Substation the nominal voltage at 220 kV was exceeded by 10% and the voltage at 400 kV end of the transmission line was 1.116 p.u. and 1.128 p.u. at Sur Power Plant and New Izki Grid Substation respectively.