Jordan's first 400 kV GIS substation completed22 February 1998
The recently completed 400 kV gas insulated switchgear (GIS) substation at Aqaba on Jordan's Red Sea coast is the first part of the EJIST interconnection project that will eventually link the power systems of Egypt, Jordan, Iraq, Syria and Turkey. The substation is also of national importance as it is the first 400 kV substation and principal point of interconnection as Jordan upgrades its present 132 kV system with a 400 kV network.
The EJIST project dates back to 1986, when a study was undertaken to establish the feasibility of setting up a Jordan/Egypt interconnection. In 1989, this grew into a full interconnection between the five countries. Such an interconnection would offer substantial benefits all round, with the potential for power sales between countries as demand fluctuates with seasonal variations and time differences. Further benefits would be the ability to share spinning reserve capacity, optimum utilisation of existing generation capacity and a reduction in the level of capital required for new power plant investments.
Following completion of the initial studies, commencement of the interconnection was delayed by the Gulf War but it was restarted in 1994. Contracts for the substation, lines and transformers in Egypt and Jordan were awarded in 1995. The tenders for the Jordan-Syria and Syria-Turkey connections have been bid and these are currently being evaluated. The Syria-Iraq and Turkey-Iraq connections will follow later. Completion of the Aqaba 400 kV substation and the Jordan-Egypt subsea link establishes the first part of the EJIST interconnection.
The substation is of particular importance to Jordan as it is a key component of plans by the National Electric Power Company (Nepco) to upgrade the country's transmission system. Electricity demand is forecast to grow from a peak load of 1000 MW in 1997 to around 1900 MW in 2010 and it has been recognised that to maintain reliable supplies during this period of growth, a 400 kV transmission system will be needed in place of the existing 132 kV one.
Aqaba is Jordan's first 400 kV substation. It comprises 11 bays of 400 kV gas insulated switchgear configured into six circuits, as follows:Egypt interconnector, with two circuit breakers Auto-transformer 1/Amman South 1, with three circuit breakers Auto-transformer 2/Amman South 2, with three circuit breakers Three circuits for generators 3, 4 and 5, each with a single circuit breaker.
Each bay includes one 420 kV, 4000 A circuit breaker, associated 420 kV, 4000 A disconnectors, earth switches, fault making earth switches and GIS backparts in a double busbar arrangement.
The substation, which was supplied by Rolls-Royce's Reyrolle Projects under a turnkey contract, is extendible to include a further Egypt interconnector, two Amman North feeders and another generator circuit. It is the principal point of connection in Nepco's new 400 kV network, as well as the connection point for the Aqaba oil fired power station, which originally comprised two 130 MW units linked to a 132 kV substation. The third unit is expected to enter service this spring, followed by Units 4 and 5 before the end of the year, bringing the total installed capacity at the power station to 650 MW.
The existing substation is connected to the new one via two 240 MVA 420/132 kV auto-transformers and a two-bay extension to the original 132 kV gas insulated switchgear. The auto-transformer circuits include three single phase 360 kV, 16 kJ/kV GIS surge arrestors.
The Jordan-Egypt interconnector circuit comprises a 13.5 km-long submarine cable installed across the Gulf of Aqaba to a new 400/500 kV substation at Naqab, and also a 500 kV transmission line across the Sinai desert to Suez.
There are cable termination stations for the oil-filled submarine cable at Taba in Egypt and also at Aqaba, each located within 300 m of the shoreline and connected to their respective substations by 10 to 20 km-long transmission lines.
The submarine cable is rated for ac operation at 600 MW but if the load exceeds this level, it can be changed to dc operation at up to 1200 MW. Allowance has been made for the establishment of a dc converter station between the substation and the terminal station, and conversion of the terminal station to accommodate the dc rated cables.
The Aqaba and Amman South substations are connected via a double circuit 325 km- long transmission line that previously operated at 132 kV. This is has been upgraded to 400 kV to establish the initial stage of the planned 400 kV transmission system.
The Rolls-Royce contract, worth around $54 million, covered turnkey supply of the 400 kV Aqaba substation, the termination station at the Aqaba end of the submarine cable, three sets of air insulated equipment to interface between the 400 kV gas insulated switchgear and the overhead lines for the Egypt and Amman South feeder circuits, the extension to the existing 132 kV GIS and the protection equipment for Naqab, which forms the link with the Egyptian grid.
Factors that were considered when evaluating the substation type to be used were:the extremely limited area which was available to accommodate the substation, 400/132 kV auto-transformers and shunt reactive compensation possible wind-blown saline pollution at the coastal site the presence of a pipeline from the fuel oil tank farm to Units 1 and 2 in the existing power plant the cost of shutting down the principal generators within the Nepco network if the fuel oil pipeline were to be relocated earthquake activity and security of the switchgear.
The land area required for a GIS solution was estimated to be approximately 20 per cent of that required for a comparable air insulated switchgear (AIS) installation. The cost comparison, which included site development costs for each type of switchgear, showed a margin of around ten per cent in favour of the AIS option but this would have required diversion of the fuel oil pipe, resulting in a lengthy shutdown of the power plant. The cost of replacement energy during the shutdown period would have made AIS option much more expensive than GIS. This resulted in the selection of SF6 insulated switchgear, combined with an AIS arrangement for the line end connected shunt reactors, capacitor voltage transformers and surge arrestors.
The Aqaba substation is the first part of the EJIST project to interconnect Egypt, Jordan, Iraq, Syria and Turkey. It is the Jordanian bussing point for the Egypt-Jordan interconnection, as well as providing the connection to the Amman South transmission line, and the current and future transmission connections for the Aqaba power station.
The switching arrangement chosen reflects the degree of security required by the different classes of circuit being controlled. The arrangement selected for the Aqaba power station generator circuits is of conventional double busbar, single circuit breaker design, which ensures that transmission network security is not impaired when switching each generator into or out of service.
The initial development of the substation caters for the double circuit line to Amman South to be operated at 400 kV. Space has been allowed for the addition of a second double circuit overhead line, routed to Amman North 400 kV substation. Security and high availability will be provided by connecting them in a breaker and half switching configuration.
The interconnection with Egypt is of strategic significance and has therefore been afforded maximum security and availability by using a double busbar, double circuit breaker configuration. This is in line with the configuration used in Egypt on the 500 kV system.
The space required to accommodate the substation equipment was an important consideration during the design phase, because the area available for development of the 400 kV installation, adjacent to the existing 132 kV one, was extremely limited. The 400 kV substation site is bounded to the west by the existing 132 kV substation, to the south by the expansion of the power station and to the north and east by the site road but more importantly by the fuel lines from the tank farm to the power station.
The site slopes significantly from north to south, which required a stepped profile to accommodate the substation and power transformers. The main part of the substation uses gas insulated switchgear, which minimizes space requirements, but in order to reduce costs, the connections to the shunt reactors associated with the transmission lines are made using air insulated switchgear.
The GIS is located at about the same level as the power station, with the outdoor yard around 3 m higher. The physical layout is a side-by-side arrangement of busbars providing an elongated substation, such that the bay spacing of the switchgear matches that of the incoming terminal towers and the 400 kV oil-filled circuits to the power plant.
Single phase reactors are used on the Egypt interconnector circuit and on each of the Amman South feeders. Three single phase 100 MVAr reactors are used in each case, while both Amman South feeders also include one 10.9 MVAr, 76 kV neutral reactor to facilitate the use of single phase, high speed autoreclose.
The outdoor section of the substation has to accommodate these reactors, together with their associated disconnectors and surge arrestors. AIS surge arrestors are used to protect the GIS from voltage transients emanating from the external power system
The space for the outdoor yard was further constrained to allow for an embankment from the site road and oil pipe, to avoid the high cost of providing retaining walls around the site perimeter. These measures enabled all the circuits required at this stage to be accommodated with space for the future Egypt and Amman North circuits. The Amman North circuits will be accommodated through construction of a retaining wall for part of the site at the eastern perimeter and the use of GIS connections to the shunt reactors
The 3 m difference in level between the outdoor portion of the substation site and the access road gave rise to problems with regard to the steepness of the road leading to the shunt reactors and so a slope of one in ten had to be adopted. Careful routing was needed for the 132 kV power cables from the transformers to the 132 kV switchgear and the 400 kV control cables from the 400 kV GIS building to the power plant control room.
The substation can be controlled from three locations:the National Control Centre, Amman, with connection via power line carrier equipment the control room at Aqaba power station, connected via fibre optics the 400 kV substation itself, where there are three modes of control from the substation's own control room, using the same computerized control system as would be used from the National Control Centre or from the control room and the power station using a hard-wired control panel located in the substation control room using local control cubicles located in the GIS building.
The interconnection between Egypt and Jordan is the point of sale of power between the two countries. The metering hardware comprises two sets of identical metering equipment at the Aqaba and Naqab ends of the submarine cable. Each set comprises two independent free-standing panels, one for export and one for import measurement. Each panel includes a main polyphase meter for MWh and MVArh measurements, three composite single phase check meters and a summator printometer. The summator is a flexible programmable unit which supports a wide range of integration, maximum demand, tariff, local printout/display and remote communication facilities.
Design and construction of substation and cable termination station involved a significant number of interfaces between contractors, in particular at the termination station, where environmental impact was an important consideration. GIS was used to minimize the visual impact of the installation, as Aqaba is developing its tourism industry to cater for visitors both to the coast and to the historic city of Petra, 100 km to the south.
The new substation therefore has a significant role in the development of that region, because part of the anticipated growth in Jordan's power demand will result from hotels that are being built there.